Merge tag 'io_uring-5.13-2021-05-07' of git://git.kernel.dk/linux-block

[mirror_ubuntu-jammy-kernel.git] / net / sunrpc / xdr.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * linux/net/sunrpc/xdr.c
 *
 * Generic XDR support.
 *
 * Copyright (C) 1995, 1996 Olaf Kirch <okir@monad.swb.de>
 */

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/kernel.h>
#include <linux/pagemap.h>
#include <linux/errno.h>
#include <linux/sunrpc/xdr.h>
#include <linux/sunrpc/msg_prot.h>
#include <linux/bvec.h>
#include <trace/events/sunrpc.h>

static void _copy_to_pages(struct page **, size_t, const char *, size_t);


/*
 * XDR functions for basic NFS types
 */
__be32 *
xdr_encode_netobj(__be32 *p, const struct xdr_netobj *obj)
{
        unsigned int    quadlen = XDR_QUADLEN(obj->len);

        p[quadlen] = 0;         /* zero trailing bytes */
        *p++ = cpu_to_be32(obj->len);
        memcpy(p, obj->data, obj->len);
        return p + XDR_QUADLEN(obj->len);
}
EXPORT_SYMBOL_GPL(xdr_encode_netobj);

__be32 *
xdr_decode_netobj(__be32 *p, struct xdr_netobj *obj)
{
        unsigned int    len;

        if ((len = be32_to_cpu(*p++)) > XDR_MAX_NETOBJ)
                return NULL;
        obj->len  = len;
        obj->data = (u8 *) p;
        return p + XDR_QUADLEN(len);
}
EXPORT_SYMBOL_GPL(xdr_decode_netobj);

/**
 * xdr_encode_opaque_fixed - Encode fixed length opaque data
 * @p: pointer to current position in XDR buffer.
 * @ptr: pointer to data to encode (or NULL)
 * @nbytes: size of data.
 *
 * Copy the array of data of length nbytes at ptr to the XDR buffer
 * at position p, then align to the next 32-bit boundary by padding
 * with zero bytes (see RFC1832).
 * Note: if ptr is NULL, only the padding is performed.
 *
 * Returns the updated current XDR buffer position
 *
 */
__be32 *xdr_encode_opaque_fixed(__be32 *p, const void *ptr, unsigned int nbytes)
{
        if (likely(nbytes != 0)) {
                unsigned int quadlen = XDR_QUADLEN(nbytes);
                unsigned int padding = (quadlen << 2) - nbytes;

                if (ptr != NULL)
                        memcpy(p, ptr, nbytes);
                if (padding != 0)
                        memset((char *)p + nbytes, 0, padding);
                p += quadlen;
        }
        return p;
}
EXPORT_SYMBOL_GPL(xdr_encode_opaque_fixed);

/**
 * xdr_encode_opaque - Encode variable length opaque data
 * @p: pointer to current position in XDR buffer.
 * @ptr: pointer to data to encode (or NULL)
 * @nbytes: size of data.
 *
 * Returns the updated current XDR buffer position
 */
__be32 *xdr_encode_opaque(__be32 *p, const void *ptr, unsigned int nbytes)
{
        *p++ = cpu_to_be32(nbytes);
        return xdr_encode_opaque_fixed(p, ptr, nbytes);
}
EXPORT_SYMBOL_GPL(xdr_encode_opaque);

__be32 *
xdr_encode_string(__be32 *p, const char *string)
{
        return xdr_encode_array(p, string, strlen(string));
}
EXPORT_SYMBOL_GPL(xdr_encode_string);

__be32 *
xdr_decode_string_inplace(__be32 *p, char **sp,
                          unsigned int *lenp, unsigned int maxlen)
{
        u32 len;

        len = be32_to_cpu(*p++);
        if (len > maxlen)
                return NULL;
        *lenp = len;
        *sp = (char *) p;
        return p + XDR_QUADLEN(len);
}
EXPORT_SYMBOL_GPL(xdr_decode_string_inplace);

/**
 * xdr_terminate_string - '\0'-terminate a string residing in an xdr_buf
 * @buf: XDR buffer where string resides
 * @len: length of string, in bytes
 *
 */
void xdr_terminate_string(const struct xdr_buf *buf, const u32 len)
{
        char *kaddr;

        kaddr = kmap_atomic(buf->pages[0]);
        kaddr[buf->page_base + len] = '\0';
        kunmap_atomic(kaddr);
}
EXPORT_SYMBOL_GPL(xdr_terminate_string);

size_t xdr_buf_pagecount(const struct xdr_buf *buf)
{
        if (!buf->page_len)
                return 0;
        return (buf->page_base + buf->page_len + PAGE_SIZE - 1) >> PAGE_SHIFT;
}

int
xdr_alloc_bvec(struct xdr_buf *buf, gfp_t gfp)
{
        size_t i, n = xdr_buf_pagecount(buf);

        if (n != 0 && buf->bvec == NULL) {
                buf->bvec = kmalloc_array(n, sizeof(buf->bvec[0]), gfp);
                if (!buf->bvec)
                        return -ENOMEM;
                for (i = 0; i < n; i++) {
                        buf->bvec[i].bv_page = buf->pages[i];
                        buf->bvec[i].bv_len = PAGE_SIZE;
                        buf->bvec[i].bv_offset = 0;
                }
        }
        return 0;
}

void
xdr_free_bvec(struct xdr_buf *buf)
{
        kfree(buf->bvec);
        buf->bvec = NULL;
}

/**
 * xdr_inline_pages - Prepare receive buffer for a large reply
 * @xdr: xdr_buf into which reply will be placed
 * @offset: expected offset where data payload will start, in bytes
 * @pages: vector of struct page pointers
 * @base: offset in first page where receive should start, in bytes
 * @len: expected size of the upper layer data payload, in bytes
 *
 */
void
xdr_inline_pages(struct xdr_buf *xdr, unsigned int offset,
                 struct page **pages, unsigned int base, unsigned int len)
{
        struct kvec *head = xdr->head;
        struct kvec *tail = xdr->tail;
        char *buf = (char *)head->iov_base;
        unsigned int buflen = head->iov_len;

        head->iov_len  = offset;

        xdr->pages = pages;
        xdr->page_base = base;
        xdr->page_len = len;

        tail->iov_base = buf + offset;
        tail->iov_len = buflen - offset;
        xdr->buflen += len;
}
EXPORT_SYMBOL_GPL(xdr_inline_pages);

/*
 * Helper routines for doing 'memmove' like operations on a struct xdr_buf
 */

/**
 * _shift_data_left_pages
 * @pages: vector of pages containing both the source and dest memory area.
 * @pgto_base: page vector address of destination
 * @pgfrom_base: page vector address of source
 * @len: number of bytes to copy
 *
 * Note: the addresses pgto_base and pgfrom_base are both calculated in
 *       the same way:
 *            if a memory area starts at byte 'base' in page 'pages[i]',
 *            then its address is given as (i << PAGE_CACHE_SHIFT) + base
 * Alse note: pgto_base must be < pgfrom_base, but the memory areas
 *      they point to may overlap.
 */
static void
_shift_data_left_pages(struct page **pages, size_t pgto_base,
                        size_t pgfrom_base, size_t len)
{
        struct page **pgfrom, **pgto;
        char *vfrom, *vto;
        size_t copy;

        BUG_ON(pgfrom_base <= pgto_base);

        if (!len)
                return;

        pgto = pages + (pgto_base >> PAGE_SHIFT);
        pgfrom = pages + (pgfrom_base >> PAGE_SHIFT);

        pgto_base &= ~PAGE_MASK;
        pgfrom_base &= ~PAGE_MASK;

        do {
                if (pgto_base >= PAGE_SIZE) {
                        pgto_base = 0;
                        pgto++;
                }
                if (pgfrom_base >= PAGE_SIZE){
                        pgfrom_base = 0;
                        pgfrom++;
                }

                copy = len;
                if (copy > (PAGE_SIZE - pgto_base))
                        copy = PAGE_SIZE - pgto_base;
                if (copy > (PAGE_SIZE - pgfrom_base))
                        copy = PAGE_SIZE - pgfrom_base;

                vto = kmap_atomic(*pgto);
                if (*pgto != *pgfrom) {
                        vfrom = kmap_atomic(*pgfrom);
                        memcpy(vto + pgto_base, vfrom + pgfrom_base, copy);
                        kunmap_atomic(vfrom);
                } else
                        memmove(vto + pgto_base, vto + pgfrom_base, copy);
                flush_dcache_page(*pgto);
                kunmap_atomic(vto);

                pgto_base += copy;
                pgfrom_base += copy;

        } while ((len -= copy) != 0);
}

/**
 * _shift_data_right_pages
 * @pages: vector of pages containing both the source and dest memory area.
 * @pgto_base: page vector address of destination
 * @pgfrom_base: page vector address of source
 * @len: number of bytes to copy
 *
 * Note: the addresses pgto_base and pgfrom_base are both calculated in
 *       the same way:
 *            if a memory area starts at byte 'base' in page 'pages[i]',
 *            then its address is given as (i << PAGE_SHIFT) + base
 * Also note: pgfrom_base must be < pgto_base, but the memory areas
 *      they point to may overlap.
 */
static void
_shift_data_right_pages(struct page **pages, size_t pgto_base,
                size_t pgfrom_base, size_t len)
{
        struct page **pgfrom, **pgto;
        char *vfrom, *vto;
        size_t copy;

        BUG_ON(pgto_base <= pgfrom_base);

        if (!len)
                return;

        pgto_base += len;
        pgfrom_base += len;

        pgto = pages + (pgto_base >> PAGE_SHIFT);
        pgfrom = pages + (pgfrom_base >> PAGE_SHIFT);

        pgto_base &= ~PAGE_MASK;
        pgfrom_base &= ~PAGE_MASK;

        do {
                /* Are any pointers crossing a page boundary? */
                if (pgto_base == 0) {
                        pgto_base = PAGE_SIZE;
                        pgto--;
                }
                if (pgfrom_base == 0) {
                        pgfrom_base = PAGE_SIZE;
                        pgfrom--;
                }

                copy = len;
                if (copy > pgto_base)
                        copy = pgto_base;
                if (copy > pgfrom_base)
                        copy = pgfrom_base;
                pgto_base -= copy;
                pgfrom_base -= copy;

                vto = kmap_atomic(*pgto);
                if (*pgto != *pgfrom) {
                        vfrom = kmap_atomic(*pgfrom);
                        memcpy(vto + pgto_base, vfrom + pgfrom_base, copy);
                        kunmap_atomic(vfrom);
                } else
                        memmove(vto + pgto_base, vto + pgfrom_base, copy);
                flush_dcache_page(*pgto);
                kunmap_atomic(vto);

        } while ((len -= copy) != 0);
}

/**
 * _copy_to_pages
 * @pages: array of pages
 * @pgbase: page vector address of destination
 * @p: pointer to source data
 * @len: length
 *
 * Copies data from an arbitrary memory location into an array of pages
 * The copy is assumed to be non-overlapping.
 */
static void
_copy_to_pages(struct page **pages, size_t pgbase, const char *p, size_t len)
{
        struct page **pgto;
        char *vto;
        size_t copy;

        if (!len)
                return;

        pgto = pages + (pgbase >> PAGE_SHIFT);
        pgbase &= ~PAGE_MASK;

        for (;;) {
                copy = PAGE_SIZE - pgbase;
                if (copy > len)
                        copy = len;

                vto = kmap_atomic(*pgto);
                memcpy(vto + pgbase, p, copy);
                kunmap_atomic(vto);

                len -= copy;
                if (len == 0)
                        break;

                pgbase += copy;
                if (pgbase == PAGE_SIZE) {
                        flush_dcache_page(*pgto);
                        pgbase = 0;
                        pgto++;
                }
                p += copy;
        }
        flush_dcache_page(*pgto);
}

/**
 * _copy_from_pages
 * @p: pointer to destination
 * @pages: array of pages
 * @pgbase: offset of source data
 * @len: length
 *
 * Copies data into an arbitrary memory location from an array of pages
 * The copy is assumed to be non-overlapping.
 */
void
_copy_from_pages(char *p, struct page **pages, size_t pgbase, size_t len)
{
        struct page **pgfrom;
        char *vfrom;
        size_t copy;

        if (!len)
                return;

        pgfrom = pages + (pgbase >> PAGE_SHIFT);
        pgbase &= ~PAGE_MASK;

        do {
                copy = PAGE_SIZE - pgbase;
                if (copy > len)
                        copy = len;

                vfrom = kmap_atomic(*pgfrom);
                memcpy(p, vfrom + pgbase, copy);
                kunmap_atomic(vfrom);

                pgbase += copy;
                if (pgbase == PAGE_SIZE) {
                        pgbase = 0;
                        pgfrom++;
                }
                p += copy;

        } while ((len -= copy) != 0);
}
EXPORT_SYMBOL_GPL(_copy_from_pages);

static void xdr_buf_iov_zero(const struct kvec *iov, unsigned int base,
                             unsigned int len)
{
        if (base >= iov->iov_len)
                return;
        if (len > iov->iov_len - base)
                len = iov->iov_len - base;
        memset(iov->iov_base + base, 0, len);
}

/**
 * xdr_buf_pages_zero
 * @buf: xdr_buf
 * @pgbase: beginning offset
 * @len: length
 */
static void xdr_buf_pages_zero(const struct xdr_buf *buf, unsigned int pgbase,
                               unsigned int len)
{
        struct page **pages = buf->pages;
        struct page **page;
        char *vpage;
        unsigned int zero;

        if (!len)
                return;
        if (pgbase >= buf->page_len) {
                xdr_buf_iov_zero(buf->tail, pgbase - buf->page_len, len);
                return;
        }
        if (pgbase + len > buf->page_len) {
                xdr_buf_iov_zero(buf->tail, 0, pgbase + len - buf->page_len);
                len = buf->page_len - pgbase;
        }

        pgbase += buf->page_base;

        page = pages + (pgbase >> PAGE_SHIFT);
        pgbase &= ~PAGE_MASK;

        do {
                zero = PAGE_SIZE - pgbase;
                if (zero > len)
                        zero = len;

                vpage = kmap_atomic(*page);
                memset(vpage + pgbase, 0, zero);
                kunmap_atomic(vpage);

                flush_dcache_page(*page);
                pgbase = 0;
                page++;

        } while ((len -= zero) != 0);
}

static unsigned int xdr_buf_pages_fill_sparse(const struct xdr_buf *buf,
                                              unsigned int buflen, gfp_t gfp)
{
        unsigned int i, npages, pagelen;

        if (!(buf->flags & XDRBUF_SPARSE_PAGES))
                return buflen;
        if (buflen <= buf->head->iov_len)
                return buflen;
        pagelen = buflen - buf->head->iov_len;
        if (pagelen > buf->page_len)
                pagelen = buf->page_len;
        npages = (pagelen + buf->page_base + PAGE_SIZE - 1) >> PAGE_SHIFT;
        for (i = 0; i < npages; i++) {
                if (!buf->pages[i])
                        continue;
                buf->pages[i] = alloc_page(gfp);
                if (likely(buf->pages[i]))
                        continue;
                buflen -= pagelen;
                pagelen = i << PAGE_SHIFT;
                if (pagelen > buf->page_base)
                        buflen += pagelen - buf->page_base;
                break;
        }
        return buflen;
}

static void xdr_buf_try_expand(struct xdr_buf *buf, unsigned int len)
{
        struct kvec *head = buf->head;
        struct kvec *tail = buf->tail;
        unsigned int sum = head->iov_len + buf->page_len + tail->iov_len;
        unsigned int free_space, newlen;

        if (sum > buf->len) {
                free_space = min_t(unsigned int, sum - buf->len, len);
                newlen = xdr_buf_pages_fill_sparse(buf, buf->len + free_space,
                                                   GFP_KERNEL);
                free_space = newlen - buf->len;
                buf->len = newlen;
                len -= free_space;
                if (!len)
                        return;
        }

        if (buf->buflen > sum) {
                /* Expand the tail buffer */
                free_space = min_t(unsigned int, buf->buflen - sum, len);
                tail->iov_len += free_space;
                buf->len += free_space;
        }
}

static void xdr_buf_tail_copy_right(const struct xdr_buf *buf,
                                    unsigned int base, unsigned int len,
                                    unsigned int shift)
{
        const struct kvec *tail = buf->tail;
        unsigned int to = base + shift;

        if (to >= tail->iov_len)
                return;
        if (len + to > tail->iov_len)
                len = tail->iov_len - to;
        memmove(tail->iov_base + to, tail->iov_base + base, len);
}

static void xdr_buf_pages_copy_right(const struct xdr_buf *buf,
                                     unsigned int base, unsigned int len,
                                     unsigned int shift)
{
        const struct kvec *tail = buf->tail;
        unsigned int to = base + shift;
        unsigned int pglen = 0;
        unsigned int talen = 0, tato = 0;

        if (base >= buf->page_len)
                return;
        if (len > buf->page_len - base)
                len = buf->page_len - base;
        if (to >= buf->page_len) {
                tato = to - buf->page_len;
                if (tail->iov_len >= len + tato)
                        talen = len;
                else if (tail->iov_len > tato)
                        talen = tail->iov_len - tato;
        } else if (len + to >= buf->page_len) {
                pglen = buf->page_len - to;
                talen = len - pglen;
                if (talen > tail->iov_len)
                        talen = tail->iov_len;
        } else
                pglen = len;

        _copy_from_pages(tail->iov_base + tato, buf->pages,
                         buf->page_base + base + pglen, talen);
        _shift_data_right_pages(buf->pages, buf->page_base + to,
                                buf->page_base + base, pglen);
}

static void xdr_buf_head_copy_right(const struct xdr_buf *buf,
                                    unsigned int base, unsigned int len,
                                    unsigned int shift)
{
        const struct kvec *head = buf->head;
        const struct kvec *tail = buf->tail;
        unsigned int to = base + shift;
        unsigned int pglen = 0, pgto = 0;
        unsigned int talen = 0, tato = 0;

        if (base >= head->iov_len)
                return;
        if (len > head->iov_len - base)
                len = head->iov_len - base;
        if (to >= buf->page_len + head->iov_len) {
                tato = to - buf->page_len - head->iov_len;
                talen = len;
        } else if (to >= head->iov_len) {
                pgto = to - head->iov_len;
                pglen = len;
                if (pgto + pglen > buf->page_len) {
                        talen = pgto + pglen - buf->page_len;
                        pglen -= talen;
                }
        } else {
                pglen = len - to;
                if (pglen > buf->page_len) {
                        talen = pglen - buf->page_len;
                        pglen = buf->page_len;
                }
        }

        len -= talen;
        base += len;
        if (talen + tato > tail->iov_len)
                talen = tail->iov_len > tato ? tail->iov_len - tato : 0;
        memcpy(tail->iov_base + tato, head->iov_base + base, talen);

        len -= pglen;
        base -= pglen;
        _copy_to_pages(buf->pages, buf->page_base + pgto, head->iov_base + base,
                       pglen);

        base -= len;
        memmove(head->iov_base + to, head->iov_base + base, len);
}

static void xdr_buf_tail_shift_right(const struct xdr_buf *buf,
                                     unsigned int base, unsigned int len,
                                     unsigned int shift)
{
        const struct kvec *tail = buf->tail;

        if (base >= tail->iov_len || !shift || !len)
                return;
        xdr_buf_tail_copy_right(buf, base, len, shift);
}

static void xdr_buf_pages_shift_right(const struct xdr_buf *buf,
                                      unsigned int base, unsigned int len,
                                      unsigned int shift)
{
        if (!shift || !len)
                return;
        if (base >= buf->page_len) {
                xdr_buf_tail_shift_right(buf, base - buf->page_len, len, shift);
                return;
        }
        if (base + len > buf->page_len)
                xdr_buf_tail_shift_right(buf, 0, base + len - buf->page_len,
                                         shift);
        xdr_buf_pages_copy_right(buf, base, len, shift);
}

static void xdr_buf_head_shift_right(const struct xdr_buf *buf,
                                     unsigned int base, unsigned int len,
                                     unsigned int shift)
{
        const struct kvec *head = buf->head;

        if (!shift)
                return;
        if (base >= head->iov_len) {
                xdr_buf_pages_shift_right(buf, head->iov_len - base, len,
                                          shift);
                return;
        }
        if (base + len > head->iov_len)
                xdr_buf_pages_shift_right(buf, 0, base + len - head->iov_len,
                                          shift);
        xdr_buf_head_copy_right(buf, base, len, shift);
}

static void xdr_buf_tail_copy_left(const struct xdr_buf *buf, unsigned int base,
                                   unsigned int len, unsigned int shift)
{
        const struct kvec *tail = buf->tail;

        if (base >= tail->iov_len)
                return;
        if (len > tail->iov_len - base)
                len = tail->iov_len - base;
        /* Shift data into head */
        if (shift > buf->page_len + base) {
                const struct kvec *head = buf->head;
                unsigned int hdto =
                        head->iov_len + buf->page_len + base - shift;
                unsigned int hdlen = len;

                if (WARN_ONCE(shift > head->iov_len + buf->page_len + base,
                              "SUNRPC: Misaligned data.\n"))
                        return;
                if (hdto + hdlen > head->iov_len)
                        hdlen = head->iov_len - hdto;
                memcpy(head->iov_base + hdto, tail->iov_base + base, hdlen);
                base += hdlen;
                len -= hdlen;
                if (!len)
                        return;
        }
        /* Shift data into pages */
        if (shift > base) {
                unsigned int pgto = buf->page_len + base - shift;
                unsigned int pglen = len;

                if (pgto + pglen > buf->page_len)
                        pglen = buf->page_len - pgto;
                _copy_to_pages(buf->pages, buf->page_base + pgto,
                               tail->iov_base + base, pglen);
                base += pglen;
                len -= pglen;
                if (!len)
                        return;
        }
        memmove(tail->iov_base + base - shift, tail->iov_base + base, len);
}

static void xdr_buf_pages_copy_left(const struct xdr_buf *buf,
                                    unsigned int base, unsigned int len,
                                    unsigned int shift)
{
        unsigned int pgto;

        if (base >= buf->page_len)
                return;
        if (len > buf->page_len - base)
                len = buf->page_len - base;
        /* Shift data into head */
        if (shift > base) {
                const struct kvec *head = buf->head;
                unsigned int hdto = head->iov_len + base - shift;
                unsigned int hdlen = len;

                if (WARN_ONCE(shift > head->iov_len + base,
                              "SUNRPC: Misaligned data.\n"))
                        return;
                if (hdto + hdlen > head->iov_len)
                        hdlen = head->iov_len - hdto;
                _copy_from_pages(head->iov_base + hdto, buf->pages,
                                 buf->page_base + base, hdlen);
                base += hdlen;
                len -= hdlen;
                if (!len)
                        return;
        }
        pgto = base - shift;
        _shift_data_left_pages(buf->pages, buf->page_base + pgto,
                               buf->page_base + base, len);
}

static void xdr_buf_tail_shift_left(const struct xdr_buf *buf,
                                    unsigned int base, unsigned int len,
                                    unsigned int shift)
{
        if (!shift || !len)
                return;
        xdr_buf_tail_copy_left(buf, base, len, shift);
}

static void xdr_buf_pages_shift_left(const struct xdr_buf *buf,
                                     unsigned int base, unsigned int len,
                                     unsigned int shift)
{
        if (!shift || !len)
                return;
        if (base >= buf->page_len) {
                xdr_buf_tail_shift_left(buf, base - buf->page_len, len, shift);
                return;
        }
        xdr_buf_pages_copy_left(buf, base, len, shift);
        len += base;
        if (len <= buf->page_len)
                return;
        xdr_buf_tail_copy_left(buf, 0, len - buf->page_len, shift);
}

/**
 * xdr_shrink_bufhead
 * @buf: xdr_buf
 * @len: new length of buf->head[0]
 *
 * Shrinks XDR buffer's header kvec buf->head[0], setting it to
 * 'len' bytes. The extra data is not lost, but is instead
 * moved into the inlined pages and/or the tail.
 */
static unsigned int xdr_shrink_bufhead(struct xdr_buf *buf, unsigned int len)
{
        struct kvec *head = buf->head;
        unsigned int shift, buflen = max(buf->len, len);

        WARN_ON_ONCE(len > head->iov_len);
        if (head->iov_len > buflen) {
                buf->buflen -= head->iov_len - buflen;
                head->iov_len = buflen;
        }
        if (len >= head->iov_len)
                return 0;
        shift = head->iov_len - len;
        xdr_buf_try_expand(buf, shift);
        xdr_buf_head_shift_right(buf, len, buflen - len, shift);
        head->iov_len = len;
        buf->buflen -= shift;
        buf->len -= shift;
        return shift;
}

/**
 * xdr_shrink_pagelen - shrinks buf->pages to @len bytes
 * @buf: xdr_buf
 * @len: new page buffer length
 *
 * The extra data is not lost, but is instead moved into buf->tail.
 * Returns the actual number of bytes moved.
 */
static unsigned int xdr_shrink_pagelen(struct xdr_buf *buf, unsigned int len)
{
        unsigned int shift, buflen = buf->len - buf->head->iov_len;

        WARN_ON_ONCE(len > buf->page_len);
        if (buf->head->iov_len >= buf->len || len > buflen)
                buflen = len;
        if (buf->page_len > buflen) {
                buf->buflen -= buf->page_len - buflen;
                buf->page_len = buflen;
        }
        if (len >= buf->page_len)
                return 0;
        shift = buf->page_len - len;
        xdr_buf_try_expand(buf, shift);
        xdr_buf_pages_shift_right(buf, len, buflen - len, shift);
        buf->page_len = len;
        buf->len -= shift;
        buf->buflen -= shift;
        return shift;
}

void
xdr_shift_buf(struct xdr_buf *buf, size_t len)
{
        xdr_shrink_bufhead(buf, buf->head->iov_len - len);
}
EXPORT_SYMBOL_GPL(xdr_shift_buf);

/**
 * xdr_stream_pos - Return the current offset from the start of the xdr_stream
 * @xdr: pointer to struct xdr_stream
 */
unsigned int xdr_stream_pos(const struct xdr_stream *xdr)
{
        return (unsigned int)(XDR_QUADLEN(xdr->buf->len) - xdr->nwords) << 2;
}
EXPORT_SYMBOL_GPL(xdr_stream_pos);

static void xdr_stream_set_pos(struct xdr_stream *xdr, unsigned int pos)
{
        unsigned int blen = xdr->buf->len;

        xdr->nwords = blen > pos ? XDR_QUADLEN(blen) - XDR_QUADLEN(pos) : 0;
}

static void xdr_stream_page_set_pos(struct xdr_stream *xdr, unsigned int pos)
{
        xdr_stream_set_pos(xdr, pos + xdr->buf->head[0].iov_len);
}

/**
 * xdr_page_pos - Return the current offset from the start of the xdr pages
 * @xdr: pointer to struct xdr_stream
 */
unsigned int xdr_page_pos(const struct xdr_stream *xdr)
{
        unsigned int pos = xdr_stream_pos(xdr);

        WARN_ON(pos < xdr->buf->head[0].iov_len);
        return pos - xdr->buf->head[0].iov_len;
}
EXPORT_SYMBOL_GPL(xdr_page_pos);

/**
 * xdr_init_encode - Initialize a struct xdr_stream for sending data.
 * @xdr: pointer to xdr_stream struct
 * @buf: pointer to XDR buffer in which to encode data
 * @p: current pointer inside XDR buffer
 * @rqst: pointer to controlling rpc_rqst, for debugging
 *
 * Note: at the moment the RPC client only passes the length of our
 *       scratch buffer in the xdr_buf's header kvec. Previously this
 *       meant we needed to call xdr_adjust_iovec() after encoding the
 *       data. With the new scheme, the xdr_stream manages the details
 *       of the buffer length, and takes care of adjusting the kvec
 *       length for us.
 */
void xdr_init_encode(struct xdr_stream *xdr, struct xdr_buf *buf, __be32 *p,
                     struct rpc_rqst *rqst)
{
        struct kvec *iov = buf->head;
        int scratch_len = buf->buflen - buf->page_len - buf->tail[0].iov_len;

        xdr_reset_scratch_buffer(xdr);
        BUG_ON(scratch_len < 0);
        xdr->buf = buf;
        xdr->iov = iov;
        xdr->p = (__be32 *)((char *)iov->iov_base + iov->iov_len);
        xdr->end = (__be32 *)((char *)iov->iov_base + scratch_len);
        BUG_ON(iov->iov_len > scratch_len);

        if (p != xdr->p && p != NULL) {
                size_t len;

                BUG_ON(p < xdr->p || p > xdr->end);
                len = (char *)p - (char *)xdr->p;
                xdr->p = p;
                buf->len += len;
                iov->iov_len += len;
        }
        xdr->rqst = rqst;
}
EXPORT_SYMBOL_GPL(xdr_init_encode);

/**
 * xdr_commit_encode - Ensure all data is written to buffer
 * @xdr: pointer to xdr_stream
 *
 * We handle encoding across page boundaries by giving the caller a
 * temporary location to write to, then later copying the data into
 * place; xdr_commit_encode does that copying.
 *
 * Normally the caller doesn't need to call this directly, as the
 * following xdr_reserve_space will do it.  But an explicit call may be
 * required at the end of encoding, or any other time when the xdr_buf
 * data might be read.
 */
inline void xdr_commit_encode(struct xdr_stream *xdr)
{
        int shift = xdr->scratch.iov_len;
        void *page;

        if (shift == 0)
                return;
        page = page_address(*xdr->page_ptr);
        memcpy(xdr->scratch.iov_base, page, shift);
        memmove(page, page + shift, (void *)xdr->p - page);
        xdr_reset_scratch_buffer(xdr);
}
EXPORT_SYMBOL_GPL(xdr_commit_encode);

static __be32 *xdr_get_next_encode_buffer(struct xdr_stream *xdr,
                size_t nbytes)
{
        __be32 *p;
        int space_left;
        int frag1bytes, frag2bytes;

        if (nbytes > PAGE_SIZE)
                goto out_overflow; /* Bigger buffers require special handling */
        if (xdr->buf->len + nbytes > xdr->buf->buflen)
                goto out_overflow; /* Sorry, we're totally out of space */
        frag1bytes = (xdr->end - xdr->p) << 2;
        frag2bytes = nbytes - frag1bytes;
        if (xdr->iov)
                xdr->iov->iov_len += frag1bytes;
        else
                xdr->buf->page_len += frag1bytes;
        xdr->page_ptr++;
        xdr->iov = NULL;
        /*
         * If the last encode didn't end exactly on a page boundary, the
         * next one will straddle boundaries.  Encode into the next
         * page, then copy it back later in xdr_commit_encode.  We use
         * the "scratch" iov to track any temporarily unused fragment of
         * space at the end of the previous buffer:
         */
        xdr_set_scratch_buffer(xdr, xdr->p, frag1bytes);
        p = page_address(*xdr->page_ptr);
        /*
         * Note this is where the next encode will start after we've
         * shifted this one back:
         */
        xdr->p = (void *)p + frag2bytes;
        space_left = xdr->buf->buflen - xdr->buf->len;
        xdr->end = (void *)p + min_t(int, space_left, PAGE_SIZE);
        xdr->buf->page_len += frag2bytes;
        xdr->buf->len += nbytes;
        return p;
out_overflow:
        trace_rpc_xdr_overflow(xdr, nbytes);
        return NULL;
}

/**
 * xdr_reserve_space - Reserve buffer space for sending
 * @xdr: pointer to xdr_stream
 * @nbytes: number of bytes to reserve
 *
 * Checks that we have enough buffer space to encode 'nbytes' more
 * bytes of data. If so, update the total xdr_buf length, and
 * adjust the length of the current kvec.
 */
__be32 * xdr_reserve_space(struct xdr_stream *xdr, size_t nbytes)
{
        __be32 *p = xdr->p;
        __be32 *q;

        xdr_commit_encode(xdr);
        /* align nbytes on the next 32-bit boundary */
        nbytes += 3;
        nbytes &= ~3;
        q = p + (nbytes >> 2);
        if (unlikely(q > xdr->end || q < p))
                return xdr_get_next_encode_buffer(xdr, nbytes);
        xdr->p = q;
        if (xdr->iov)
                xdr->iov->iov_len += nbytes;
        else
                xdr->buf->page_len += nbytes;
        xdr->buf->len += nbytes;
        return p;
}
EXPORT_SYMBOL_GPL(xdr_reserve_space);


/**
 * xdr_reserve_space_vec - Reserves a large amount of buffer space for sending
 * @xdr: pointer to xdr_stream
 * @vec: pointer to a kvec array
 * @nbytes: number of bytes to reserve
 *
 * Reserves enough buffer space to encode 'nbytes' of data and stores the
 * pointers in 'vec'. The size argument passed to xdr_reserve_space() is
 * determined based on the number of bytes remaining in the current page to
 * avoid invalidating iov_base pointers when xdr_commit_encode() is called.
 */
int xdr_reserve_space_vec(struct xdr_stream *xdr, struct kvec *vec, size_t nbytes)
{
        int thislen;
        int v = 0;
        __be32 *p;

        /*
         * svcrdma requires every READ payload to start somewhere
         * in xdr->pages.
         */
        if (xdr->iov == xdr->buf->head) {
                xdr->iov = NULL;
                xdr->end = xdr->p;
        }

        while (nbytes) {
                thislen = xdr->buf->page_len % PAGE_SIZE;
                thislen = min_t(size_t, nbytes, PAGE_SIZE - thislen);

                p = xdr_reserve_space(xdr, thislen);
                if (!p)
                        return -EIO;

                vec[v].iov_base = p;
                vec[v].iov_len = thislen;
                v++;
                nbytes -= thislen;
        }

        return v;
}
EXPORT_SYMBOL_GPL(xdr_reserve_space_vec);

/**
 * xdr_truncate_encode - truncate an encode buffer
 * @xdr: pointer to xdr_stream
 * @len: new length of buffer
 *
 * Truncates the xdr stream, so that xdr->buf->len == len,
 * and xdr->p points at offset len from the start of the buffer, and
 * head, tail, and page lengths are adjusted to correspond.
 *
 * If this means moving xdr->p to a different buffer, we assume that
 * the end pointer should be set to the end of the current page,
 * except in the case of the head buffer when we assume the head
 * buffer's current length represents the end of the available buffer.
 *
 * This is *not* safe to use on a buffer that already has inlined page
 * cache pages (as in a zero-copy server read reply), except for the
 * simple case of truncating from one position in the tail to another.
 *
 */
void xdr_truncate_encode(struct xdr_stream *xdr, size_t len)
{
        struct xdr_buf *buf = xdr->buf;
        struct kvec *head = buf->head;
        struct kvec *tail = buf->tail;
        int fraglen;
        int new;

        if (len > buf->len) {
                WARN_ON_ONCE(1);
                return;
        }
        xdr_commit_encode(xdr);

        fraglen = min_t(int, buf->len - len, tail->iov_len);
        tail->iov_len -= fraglen;
        buf->len -= fraglen;
        if (tail->iov_len) {
                xdr->p = tail->iov_base + tail->iov_len;
                WARN_ON_ONCE(!xdr->end);
                WARN_ON_ONCE(!xdr->iov);
                return;
        }
        WARN_ON_ONCE(fraglen);
        fraglen = min_t(int, buf->len - len, buf->page_len);
        buf->page_len -= fraglen;
        buf->len -= fraglen;

        new = buf->page_base + buf->page_len;

        xdr->page_ptr = buf->pages + (new >> PAGE_SHIFT);

        if (buf->page_len) {
                xdr->p = page_address(*xdr->page_ptr);
                xdr->end = (void *)xdr->p + PAGE_SIZE;
                xdr->p = (void *)xdr->p + (new % PAGE_SIZE);
                WARN_ON_ONCE(xdr->iov);
                return;
        }
        if (fraglen)
                xdr->end = head->iov_base + head->iov_len;
        /* (otherwise assume xdr->end is already set) */
        xdr->page_ptr--;
        head->iov_len = len;
        buf->len = len;
        xdr->p = head->iov_base + head->iov_len;
        xdr->iov = buf->head;
}
EXPORT_SYMBOL(xdr_truncate_encode);

/**
 * xdr_restrict_buflen - decrease available buffer space
 * @xdr: pointer to xdr_stream
 * @newbuflen: new maximum number of bytes available
 *
 * Adjust our idea of how much space is available in the buffer.
 * If we've already used too much space in the buffer, returns -1.
 * If the available space is already smaller than newbuflen, returns 0
 * and does nothing.  Otherwise, adjusts xdr->buf->buflen to newbuflen
 * and ensures xdr->end is set at most offset newbuflen from the start
 * of the buffer.
 */
int xdr_restrict_buflen(struct xdr_stream *xdr, int newbuflen)
{
        struct xdr_buf *buf = xdr->buf;
        int left_in_this_buf = (void *)xdr->end - (void *)xdr->p;
        int end_offset = buf->len + left_in_this_buf;

        if (newbuflen < 0 || newbuflen < buf->len)
                return -1;
        if (newbuflen > buf->buflen)
                return 0;
        if (newbuflen < end_offset)
                xdr->end = (void *)xdr->end + newbuflen - end_offset;
        buf->buflen = newbuflen;
        return 0;
}
EXPORT_SYMBOL(xdr_restrict_buflen);

/**
 * xdr_write_pages - Insert a list of pages into an XDR buffer for sending
 * @xdr: pointer to xdr_stream
 * @pages: list of pages
 * @base: offset of first byte
 * @len: length of data in bytes
 *
 */
void xdr_write_pages(struct xdr_stream *xdr, struct page **pages, unsigned int base,
                 unsigned int len)
{
        struct xdr_buf *buf = xdr->buf;
        struct kvec *iov = buf->tail;
        buf->pages = pages;
        buf->page_base = base;
        buf->page_len = len;

        iov->iov_base = (char *)xdr->p;
        iov->iov_len  = 0;
        xdr->iov = iov;

        if (len & 3) {
                unsigned int pad = 4 - (len & 3);

                BUG_ON(xdr->p >= xdr->end);
                iov->iov_base = (char *)xdr->p + (len & 3);
                iov->iov_len  += pad;
                len += pad;
                *xdr->p++ = 0;
        }
        buf->buflen += len;
        buf->len += len;
}
EXPORT_SYMBOL_GPL(xdr_write_pages);

static unsigned int xdr_set_iov(struct xdr_stream *xdr, struct kvec *iov,
                                unsigned int base, unsigned int len)
{
        if (len > iov->iov_len)
                len = iov->iov_len;
        if (unlikely(base > len))
                base = len;
        xdr->p = (__be32*)(iov->iov_base + base);
        xdr->end = (__be32*)(iov->iov_base + len);
        xdr->iov = iov;
        xdr->page_ptr = NULL;
        return len - base;
}

static unsigned int xdr_set_tail_base(struct xdr_stream *xdr,
                                      unsigned int base, unsigned int len)
{
        struct xdr_buf *buf = xdr->buf;

        xdr_stream_set_pos(xdr, base + buf->page_len + buf->head->iov_len);
        return xdr_set_iov(xdr, buf->tail, base, len);
}

static unsigned int xdr_set_page_base(struct xdr_stream *xdr,
                                      unsigned int base, unsigned int len)
{
        unsigned int pgnr;
        unsigned int maxlen;
        unsigned int pgoff;
        unsigned int pgend;
        void *kaddr;

        maxlen = xdr->buf->page_len;
        if (base >= maxlen) {
                base = maxlen;
                maxlen = 0;
        } else
                maxlen -= base;
        if (len > maxlen)
                len = maxlen;

        xdr_stream_page_set_pos(xdr, base);
        base += xdr->buf->page_base;

        pgnr = base >> PAGE_SHIFT;
        xdr->page_ptr = &xdr->buf->pages[pgnr];
        kaddr = page_address(*xdr->page_ptr);

        pgoff = base & ~PAGE_MASK;
        xdr->p = (__be32*)(kaddr + pgoff);

        pgend = pgoff + len;
        if (pgend > PAGE_SIZE)
                pgend = PAGE_SIZE;
        xdr->end = (__be32*)(kaddr + pgend);
        xdr->iov = NULL;
        return len;
}

static void xdr_set_page(struct xdr_stream *xdr, unsigned int base,
                         unsigned int len)
{
        if (xdr_set_page_base(xdr, base, len) == 0) {
                base -= xdr->buf->page_len;
                xdr_set_tail_base(xdr, base, len);
        }
}

static void xdr_set_next_page(struct xdr_stream *xdr)
{
        unsigned int newbase;

        newbase = (1 + xdr->page_ptr - xdr->buf->pages) << PAGE_SHIFT;
        newbase -= xdr->buf->page_base;
        if (newbase < xdr->buf->page_len)
                xdr_set_page_base(xdr, newbase, xdr_stream_remaining(xdr));
        else
                xdr_set_tail_base(xdr, 0, xdr_stream_remaining(xdr));
}

static bool xdr_set_next_buffer(struct xdr_stream *xdr)
{
        if (xdr->page_ptr != NULL)
                xdr_set_next_page(xdr);
        else if (xdr->iov == xdr->buf->head)
                xdr_set_page(xdr, 0, xdr_stream_remaining(xdr));
        return xdr->p != xdr->end;
}

/**
 * xdr_init_decode - Initialize an xdr_stream for decoding data.
 * @xdr: pointer to xdr_stream struct
 * @buf: pointer to XDR buffer from which to decode data
 * @p: current pointer inside XDR buffer
 * @rqst: pointer to controlling rpc_rqst, for debugging
 */
void xdr_init_decode(struct xdr_stream *xdr, struct xdr_buf *buf, __be32 *p,
                     struct rpc_rqst *rqst)
{
        xdr->buf = buf;
        xdr_reset_scratch_buffer(xdr);
        xdr->nwords = XDR_QUADLEN(buf->len);
        if (xdr_set_iov(xdr, buf->head, 0, buf->len) == 0 &&
            xdr_set_page_base(xdr, 0, buf->len) == 0)
                xdr_set_iov(xdr, buf->tail, 0, buf->len);
        if (p != NULL && p > xdr->p && xdr->end >= p) {
                xdr->nwords -= p - xdr->p;
                xdr->p = p;
        }
        xdr->rqst = rqst;
}
EXPORT_SYMBOL_GPL(xdr_init_decode);

/**
 * xdr_init_decode_pages - Initialize an xdr_stream for decoding into pages
 * @xdr: pointer to xdr_stream struct
 * @buf: pointer to XDR buffer from which to decode data
 * @pages: list of pages to decode into
 * @len: length in bytes of buffer in pages
 */
void xdr_init_decode_pages(struct xdr_stream *xdr, struct xdr_buf *buf,
                           struct page **pages, unsigned int len)
{
        memset(buf, 0, sizeof(*buf));
        buf->pages =  pages;
        buf->page_len =  len;
        buf->buflen =  len;
        buf->len = len;
        xdr_init_decode(xdr, buf, NULL, NULL);
}
EXPORT_SYMBOL_GPL(xdr_init_decode_pages);

static __be32 * __xdr_inline_decode(struct xdr_stream *xdr, size_t nbytes)
{
        unsigned int nwords = XDR_QUADLEN(nbytes);
        __be32 *p = xdr->p;
        __be32 *q = p + nwords;

        if (unlikely(nwords > xdr->nwords || q > xdr->end || q < p))
                return NULL;
        xdr->p = q;
        xdr->nwords -= nwords;
        return p;
}

static __be32 *xdr_copy_to_scratch(struct xdr_stream *xdr, size_t nbytes)
{
        __be32 *p;
        char *cpdest = xdr->scratch.iov_base;
        size_t cplen = (char *)xdr->end - (char *)xdr->p;

        if (nbytes > xdr->scratch.iov_len)
                goto out_overflow;
        p = __xdr_inline_decode(xdr, cplen);
        if (p == NULL)
                return NULL;
        memcpy(cpdest, p, cplen);
        if (!xdr_set_next_buffer(xdr))
                goto out_overflow;
        cpdest += cplen;
        nbytes -= cplen;
        p = __xdr_inline_decode(xdr, nbytes);
        if (p == NULL)
                return NULL;
        memcpy(cpdest, p, nbytes);
        return xdr->scratch.iov_base;
out_overflow:
        trace_rpc_xdr_overflow(xdr, nbytes);
        return NULL;
}

/**
 * xdr_inline_decode - Retrieve XDR data to decode
 * @xdr: pointer to xdr_stream struct
 * @nbytes: number of bytes of data to decode
 *
 * Check if the input buffer is long enough to enable us to decode
 * 'nbytes' more bytes of data starting at the current position.
 * If so return the current pointer, then update the current
 * pointer position.
 */
__be32 * xdr_inline_decode(struct xdr_stream *xdr, size_t nbytes)
{
        __be32 *p;

        if (unlikely(nbytes == 0))
                return xdr->p;
        if (xdr->p == xdr->end && !xdr_set_next_buffer(xdr))
                goto out_overflow;
        p = __xdr_inline_decode(xdr, nbytes);
        if (p != NULL)
                return p;
        return xdr_copy_to_scratch(xdr, nbytes);
out_overflow:
        trace_rpc_xdr_overflow(xdr, nbytes);
        return NULL;
}
EXPORT_SYMBOL_GPL(xdr_inline_decode);

static void xdr_realign_pages(struct xdr_stream *xdr)
{
        struct xdr_buf *buf = xdr->buf;
        struct kvec *iov = buf->head;
        unsigned int cur = xdr_stream_pos(xdr);
        unsigned int copied;

        /* Realign pages to current pointer position */
        if (iov->iov_len > cur) {
                copied = xdr_shrink_bufhead(buf, cur);
                trace_rpc_xdr_alignment(xdr, cur, copied);
                xdr_set_page(xdr, 0, buf->page_len);
        }
}

static unsigned int xdr_align_pages(struct xdr_stream *xdr, unsigned int len)
{
        struct xdr_buf *buf = xdr->buf;
        unsigned int nwords = XDR_QUADLEN(len);
        unsigned int copied;

        if (xdr->nwords == 0)
                return 0;

        xdr_realign_pages(xdr);
        if (nwords > xdr->nwords) {
                nwords = xdr->nwords;
                len = nwords << 2;
        }
        if (buf->page_len <= len)
                len = buf->page_len;
        else if (nwords < xdr->nwords) {
                /* Truncate page data and move it into the tail */
                copied = xdr_shrink_pagelen(buf, len);
                trace_rpc_xdr_alignment(xdr, len, copied);
        }
        return len;
}

/**
 * xdr_read_pages - align page-based XDR data to current pointer position
 * @xdr: pointer to xdr_stream struct
 * @len: number of bytes of page data
 *
 * Moves data beyond the current pointer position from the XDR head[] buffer
 * into the page list. Any data that lies beyond current position + @len
 * bytes is moved into the XDR tail[]. The xdr_stream current position is
 * then advanced past that data to align to the next XDR object in the tail.
 *
 * Returns the number of XDR encoded bytes now contained in the pages
 */
unsigned int xdr_read_pages(struct xdr_stream *xdr, unsigned int len)
{
        unsigned int nwords = XDR_QUADLEN(len);
        unsigned int base, end, pglen;

        pglen = xdr_align_pages(xdr, nwords << 2);
        if (pglen == 0)
                return 0;

        base = (nwords << 2) - pglen;
        end = xdr_stream_remaining(xdr) - pglen;

        xdr_set_tail_base(xdr, base, end);
        return len <= pglen ? len : pglen;
}
EXPORT_SYMBOL_GPL(xdr_read_pages);

unsigned int xdr_align_data(struct xdr_stream *xdr, unsigned int offset,
                            unsigned int length)
{
        struct xdr_buf *buf = xdr->buf;
        unsigned int from, bytes, len;
        unsigned int shift;

        xdr_realign_pages(xdr);
        from = xdr_page_pos(xdr);

        if (from >= buf->page_len + buf->tail->iov_len)
                return 0;
        if (from + buf->head->iov_len >= buf->len)
                return 0;

        len = buf->len - buf->head->iov_len;

        /* We only shift data left! */
        if (WARN_ONCE(from < offset, "SUNRPC: misaligned data src=%u dst=%u\n",
                      from, offset))
                return 0;
        if (WARN_ONCE(offset > buf->page_len,
                      "SUNRPC: buffer overflow. offset=%u, page_len=%u\n",
                      offset, buf->page_len))
                return 0;

        /* Move page data to the left */
        shift = from - offset;
        xdr_buf_pages_shift_left(buf, from, len, shift);

        bytes = xdr_stream_remaining(xdr);
        if (length > bytes)
                length = bytes;
        bytes -= length;

        xdr->buf->len -= shift;
        xdr_set_page(xdr, offset + length, bytes);
        return length;
}
EXPORT_SYMBOL_GPL(xdr_align_data);

unsigned int xdr_expand_hole(struct xdr_stream *xdr, unsigned int offset,
                             unsigned int length)
{
        struct xdr_buf *buf = xdr->buf;
        unsigned int from, to, shift;

        xdr_realign_pages(xdr);
        from = xdr_page_pos(xdr);
        to = xdr_align_size(offset + length);

        /* Could the hole be behind us? */
        if (to > from) {
                unsigned int buflen = buf->len - buf->head->iov_len;
                shift = to - from;
                xdr_buf_try_expand(buf, shift);
                xdr_buf_pages_shift_right(buf, from, buflen, shift);
                xdr_set_page(xdr, to, xdr_stream_remaining(xdr));
        } else if (to != from)
                xdr_align_data(xdr, to, 0);
        xdr_buf_pages_zero(buf, offset, length);

        return length;
}
EXPORT_SYMBOL_GPL(xdr_expand_hole);

/**
 * xdr_enter_page - decode data from the XDR page
 * @xdr: pointer to xdr_stream struct
 * @len: number of bytes of page data
 *
 * Moves data beyond the current pointer position from the XDR head[] buffer
 * into the page list. Any data that lies beyond current position + "len"
 * bytes is moved into the XDR tail[]. The current pointer is then
 * repositioned at the beginning of the first XDR page.
 */
void xdr_enter_page(struct xdr_stream *xdr, unsigned int len)
{
        len = xdr_align_pages(xdr, len);
        /*
         * Position current pointer at beginning of tail, and
         * set remaining message length.
         */
        if (len != 0)
                xdr_set_page_base(xdr, 0, len);
}
EXPORT_SYMBOL_GPL(xdr_enter_page);

static const struct kvec empty_iov = {.iov_base = NULL, .iov_len = 0};

void xdr_buf_from_iov(const struct kvec *iov, struct xdr_buf *buf)
{
        buf->head[0] = *iov;
        buf->tail[0] = empty_iov;
        buf->page_len = 0;
        buf->buflen = buf->len = iov->iov_len;
}
EXPORT_SYMBOL_GPL(xdr_buf_from_iov);

/**
 * xdr_buf_subsegment - set subbuf to a portion of buf
 * @buf: an xdr buffer
 * @subbuf: the result buffer
 * @base: beginning of range in bytes
 * @len: length of range in bytes
 *
 * sets @subbuf to an xdr buffer representing the portion of @buf of
 * length @len starting at offset @base.
 *
 * @buf and @subbuf may be pointers to the same struct xdr_buf.
 *
 * Returns -1 if base of length are out of bounds.
 */
int xdr_buf_subsegment(const struct xdr_buf *buf, struct xdr_buf *subbuf,
                       unsigned int base, unsigned int len)
{
        subbuf->buflen = subbuf->len = len;
        if (base < buf->head[0].iov_len) {
                subbuf->head[0].iov_base = buf->head[0].iov_base + base;
                subbuf->head[0].iov_len = min_t(unsigned int, len,
                                                buf->head[0].iov_len - base);
                len -= subbuf->head[0].iov_len;
                base = 0;
        } else {
                base -= buf->head[0].iov_len;
                subbuf->head[0].iov_base = buf->head[0].iov_base;
                subbuf->head[0].iov_len = 0;
        }

        if (base < buf->page_len) {
                subbuf->page_len = min(buf->page_len - base, len);
                base += buf->page_base;
                subbuf->page_base = base & ~PAGE_MASK;
                subbuf->pages = &buf->pages[base >> PAGE_SHIFT];
                len -= subbuf->page_len;
                base = 0;
        } else {
                base -= buf->page_len;
                subbuf->pages = buf->pages;
                subbuf->page_base = 0;
                subbuf->page_len = 0;
        }

        if (base < buf->tail[0].iov_len) {
                subbuf->tail[0].iov_base = buf->tail[0].iov_base + base;
                subbuf->tail[0].iov_len = min_t(unsigned int, len,
                                                buf->tail[0].iov_len - base);
                len -= subbuf->tail[0].iov_len;
                base = 0;
        } else {
                base -= buf->tail[0].iov_len;
                subbuf->tail[0].iov_base = buf->tail[0].iov_base;
                subbuf->tail[0].iov_len = 0;
        }

        if (base || len)
                return -1;
        return 0;
}
EXPORT_SYMBOL_GPL(xdr_buf_subsegment);

/**
 * xdr_stream_subsegment - set @subbuf to a portion of @xdr
 * @xdr: an xdr_stream set up for decoding
 * @subbuf: the result buffer
 * @nbytes: length of @xdr to extract, in bytes
 *
 * Sets up @subbuf to represent a portion of @xdr. The portion
 * starts at the current offset in @xdr, and extends for a length
 * of @nbytes. If this is successful, @xdr is advanced to the next
 * position following that portion.
 *
 * Return values:
 *   %true: @subbuf has been initialized, and @xdr has been advanced.
 *   %false: a bounds error has occurred
 */
bool xdr_stream_subsegment(struct xdr_stream *xdr, struct xdr_buf *subbuf,
                           unsigned int nbytes)
{
        unsigned int remaining, offset, len;

        if (xdr_buf_subsegment(xdr->buf, subbuf, xdr_stream_pos(xdr), nbytes))
                return false;

        if (subbuf->head[0].iov_len)
                if (!__xdr_inline_decode(xdr, subbuf->head[0].iov_len))
                        return false;

        remaining = subbuf->page_len;
        offset = subbuf->page_base;
        while (remaining) {
                len = min_t(unsigned int, remaining, PAGE_SIZE) - offset;

                if (xdr->p == xdr->end && !xdr_set_next_buffer(xdr))
                        return false;
                if (!__xdr_inline_decode(xdr, len))
                        return false;

                remaining -= len;
                offset = 0;
        }

        return true;
}
EXPORT_SYMBOL_GPL(xdr_stream_subsegment);

/**
 * xdr_buf_trim - lop at most "len" bytes off the end of "buf"
 * @buf: buf to be trimmed
 * @len: number of bytes to reduce "buf" by
 *
 * Trim an xdr_buf by the given number of bytes by fixing up the lengths. Note
 * that it's possible that we'll trim less than that amount if the xdr_buf is
 * too small, or if (for instance) it's all in the head and the parser has
 * already read too far into it.
 */
void xdr_buf_trim(struct xdr_buf *buf, unsigned int len)
{
        size_t cur;
        unsigned int trim = len;

        if (buf->tail[0].iov_len) {
                cur = min_t(size_t, buf->tail[0].iov_len, trim);
                buf->tail[0].iov_len -= cur;
                trim -= cur;
                if (!trim)
                        goto fix_len;
        }

        if (buf->page_len) {
                cur = min_t(unsigned int, buf->page_len, trim);
                buf->page_len -= cur;
                trim -= cur;
                if (!trim)
                        goto fix_len;
        }

        if (buf->head[0].iov_len) {
                cur = min_t(size_t, buf->head[0].iov_len, trim);
                buf->head[0].iov_len -= cur;
                trim -= cur;
        }
fix_len:
        buf->len -= (len - trim);
}
EXPORT_SYMBOL_GPL(xdr_buf_trim);

static void __read_bytes_from_xdr_buf(const struct xdr_buf *subbuf,
                                      void *obj, unsigned int len)
{
        unsigned int this_len;

        this_len = min_t(unsigned int, len, subbuf->head[0].iov_len);
        memcpy(obj, subbuf->head[0].iov_base, this_len);
        len -= this_len;
        obj += this_len;
        this_len = min_t(unsigned int, len, subbuf->page_len);
        _copy_from_pages(obj, subbuf->pages, subbuf->page_base, this_len);
        len -= this_len;
        obj += this_len;
        this_len = min_t(unsigned int, len, subbuf->tail[0].iov_len);
        memcpy(obj, subbuf->tail[0].iov_base, this_len);
}

/* obj is assumed to point to allocated memory of size at least len: */
int read_bytes_from_xdr_buf(const struct xdr_buf *buf, unsigned int base,
                            void *obj, unsigned int len)
{
        struct xdr_buf subbuf;
        int status;

        status = xdr_buf_subsegment(buf, &subbuf, base, len);
        if (status != 0)
                return status;
        __read_bytes_from_xdr_buf(&subbuf, obj, len);
        return 0;
}
EXPORT_SYMBOL_GPL(read_bytes_from_xdr_buf);

static void __write_bytes_to_xdr_buf(const struct xdr_buf *subbuf,
                                     void *obj, unsigned int len)
{
        unsigned int this_len;

        this_len = min_t(unsigned int, len, subbuf->head[0].iov_len);
        memcpy(subbuf->head[0].iov_base, obj, this_len);
        len -= this_len;
        obj += this_len;
        this_len = min_t(unsigned int, len, subbuf->page_len);
        _copy_to_pages(subbuf->pages, subbuf->page_base, obj, this_len);
        len -= this_len;
        obj += this_len;
        this_len = min_t(unsigned int, len, subbuf->tail[0].iov_len);
        memcpy(subbuf->tail[0].iov_base, obj, this_len);
}

/* obj is assumed to point to allocated memory of size at least len: */
int write_bytes_to_xdr_buf(const struct xdr_buf *buf, unsigned int base,
                           void *obj, unsigned int len)
{
        struct xdr_buf subbuf;
        int status;

        status = xdr_buf_subsegment(buf, &subbuf, base, len);
        if (status != 0)
                return status;
        __write_bytes_to_xdr_buf(&subbuf, obj, len);
        return 0;
}
EXPORT_SYMBOL_GPL(write_bytes_to_xdr_buf);

int xdr_decode_word(const struct xdr_buf *buf, unsigned int base, u32 *obj)
{
        __be32  raw;
        int     status;

        status = read_bytes_from_xdr_buf(buf, base, &raw, sizeof(*obj));
        if (status)
                return status;
        *obj = be32_to_cpu(raw);
        return 0;
}
EXPORT_SYMBOL_GPL(xdr_decode_word);

int xdr_encode_word(const struct xdr_buf *buf, unsigned int base, u32 obj)
{
        __be32  raw = cpu_to_be32(obj);

        return write_bytes_to_xdr_buf(buf, base, &raw, sizeof(obj));
}
EXPORT_SYMBOL_GPL(xdr_encode_word);

/* Returns 0 on success, or else a negative error code. */
static int xdr_xcode_array2(const struct xdr_buf *buf, unsigned int base,
                            struct xdr_array2_desc *desc, int encode)
{
        char *elem = NULL, *c;
        unsigned int copied = 0, todo, avail_here;
        struct page **ppages = NULL;
        int err;

        if (encode) {
                if (xdr_encode_word(buf, base, desc->array_len) != 0)
                        return -EINVAL;
        } else {
                if (xdr_decode_word(buf, base, &desc->array_len) != 0 ||
                    desc->array_len > desc->array_maxlen ||
                    (unsigned long) base + 4 + desc->array_len *
                                    desc->elem_size > buf->len)
                        return -EINVAL;
        }
        base += 4;

        if (!desc->xcode)
                return 0;

        todo = desc->array_len * desc->elem_size;

        /* process head */
        if (todo && base < buf->head->iov_len) {
                c = buf->head->iov_base + base;
                avail_here = min_t(unsigned int, todo,
                                   buf->head->iov_len - base);
                todo -= avail_here;

                while (avail_here >= desc->elem_size) {
                        err = desc->xcode(desc, c);
                        if (err)
                                goto out;
                        c += desc->elem_size;
                        avail_here -= desc->elem_size;
                }
                if (avail_here) {
                        if (!elem) {
                                elem = kmalloc(desc->elem_size, GFP_KERNEL);
                                err = -ENOMEM;
                                if (!elem)
                                        goto out;
                        }
                        if (encode) {
                                err = desc->xcode(desc, elem);
                                if (err)
                                        goto out;
                                memcpy(c, elem, avail_here);
                        } else
                                memcpy(elem, c, avail_here);
                        copied = avail_here;
                }
                base = buf->head->iov_len;  /* align to start of pages */
        }

        /* process pages array */
        base -= buf->head->iov_len;
        if (todo && base < buf->page_len) {
                unsigned int avail_page;

                avail_here = min(todo, buf->page_len - base);
                todo -= avail_here;

                base += buf->page_base;
                ppages = buf->pages + (base >> PAGE_SHIFT);
                base &= ~PAGE_MASK;
                avail_page = min_t(unsigned int, PAGE_SIZE - base,
                                        avail_here);
                c = kmap(*ppages) + base;

                while (avail_here) {
                        avail_here -= avail_page;
                        if (copied || avail_page < desc->elem_size) {
                                unsigned int l = min(avail_page,
                                        desc->elem_size - copied);
                                if (!elem) {
                                        elem = kmalloc(desc->elem_size,
                                                       GFP_KERNEL);
                                        err = -ENOMEM;
                                        if (!elem)
                                                goto out;
                                }
                                if (encode) {
                                        if (!copied) {
                                                err = desc->xcode(desc, elem);
                                                if (err)
                                                        goto out;
                                        }
                                        memcpy(c, elem + copied, l);
                                        copied += l;
                                        if (copied == desc->elem_size)
                                                copied = 0;
                                } else {
                                        memcpy(elem + copied, c, l);
                                        copied += l;
                                        if (copied == desc->elem_size) {
                                                err = desc->xcode(desc, elem);
                                                if (err)
                                                        goto out;
                                                copied = 0;
                                        }
                                }
                                avail_page -= l;
                                c += l;
                        }
                        while (avail_page >= desc->elem_size) {
                                err = desc->xcode(desc, c);
                                if (err)
                                        goto out;
                                c += desc->elem_size;
                                avail_page -= desc->elem_size;
                        }
                        if (avail_page) {
                                unsigned int l = min(avail_page,
                                            desc->elem_size - copied);
                                if (!elem) {
                                        elem = kmalloc(desc->elem_size,
                                                       GFP_KERNEL);
                                        err = -ENOMEM;
                                        if (!elem)
                                                goto out;
                                }
                                if (encode) {
                                        if (!copied) {
                                                err = desc->xcode(desc, elem);
                                                if (err)
                                                        goto out;
                                        }
                                        memcpy(c, elem + copied, l);
                                        copied += l;
                                        if (copied == desc->elem_size)
                                                copied = 0;
                                } else {
                                        memcpy(elem + copied, c, l);
                                        copied += l;
                                        if (copied == desc->elem_size) {
                                                err = desc->xcode(desc, elem);
                                                if (err)
                                                        goto out;
                                                copied = 0;
                                        }
                                }
                        }
                        if (avail_here) {
                                kunmap(*ppages);
                                ppages++;
                                c = kmap(*ppages);
                        }

                        avail_page = min(avail_here,
                                 (unsigned int) PAGE_SIZE);
                }
                base = buf->page_len;  /* align to start of tail */
        }

        /* process tail */
        base -= buf->page_len;
        if (todo) {
                c = buf->tail->iov_base + base;
                if (copied) {
                        unsigned int l = desc->elem_size - copied;

                        if (encode)
                                memcpy(c, elem + copied, l);
                        else {
                                memcpy(elem + copied, c, l);
                                err = desc->xcode(desc, elem);
                                if (err)
                                        goto out;
                        }
                        todo -= l;
                        c += l;
                }
                while (todo) {
                        err = desc->xcode(desc, c);
                        if (err)
                                goto out;
                        c += desc->elem_size;
                        todo -= desc->elem_size;
                }
        }
        err = 0;

out:
        kfree(elem);
        if (ppages)
                kunmap(*ppages);
        return err;
}

int xdr_decode_array2(const struct xdr_buf *buf, unsigned int base,
                      struct xdr_array2_desc *desc)
{
        if (base >= buf->len)
                return -EINVAL;

        return xdr_xcode_array2(buf, base, desc, 0);
}
EXPORT_SYMBOL_GPL(xdr_decode_array2);

int xdr_encode_array2(const struct xdr_buf *buf, unsigned int base,
                      struct xdr_array2_desc *desc)
{
        if ((unsigned long) base + 4 + desc->array_len * desc->elem_size >
            buf->head->iov_len + buf->page_len + buf->tail->iov_len)
                return -EINVAL;

        return xdr_xcode_array2(buf, base, desc, 1);
}
EXPORT_SYMBOL_GPL(xdr_encode_array2);

int xdr_process_buf(const struct xdr_buf *buf, unsigned int offset,
                    unsigned int len,
                    int (*actor)(struct scatterlist *, void *), void *data)
{
        int i, ret = 0;
        unsigned int page_len, thislen, page_offset;
        struct scatterlist      sg[1];

        sg_init_table(sg, 1);

        if (offset >= buf->head[0].iov_len) {
                offset -= buf->head[0].iov_len;
        } else {
                thislen = buf->head[0].iov_len - offset;
                if (thislen > len)
                        thislen = len;
                sg_set_buf(sg, buf->head[0].iov_base + offset, thislen);
                ret = actor(sg, data);
                if (ret)
                        goto out;
                offset = 0;
                len -= thislen;
        }
        if (len == 0)
                goto out;

        if (offset >= buf->page_len) {
                offset -= buf->page_len;
        } else {
                page_len = buf->page_len - offset;
                if (page_len > len)
                        page_len = len;
                len -= page_len;
                page_offset = (offset + buf->page_base) & (PAGE_SIZE - 1);
                i = (offset + buf->page_base) >> PAGE_SHIFT;
                thislen = PAGE_SIZE - page_offset;
                do {
                        if (thislen > page_len)
                                thislen = page_len;
                        sg_set_page(sg, buf->pages[i], thislen, page_offset);
                        ret = actor(sg, data);
                        if (ret)
                                goto out;
                        page_len -= thislen;
                        i++;
                        page_offset = 0;
                        thislen = PAGE_SIZE;
                } while (page_len != 0);
                offset = 0;
        }
        if (len == 0)
                goto out;
        if (offset < buf->tail[0].iov_len) {
                thislen = buf->tail[0].iov_len - offset;
                if (thislen > len)
                        thislen = len;
                sg_set_buf(sg, buf->tail[0].iov_base + offset, thislen);
                ret = actor(sg, data);
                len -= thislen;
        }
        if (len != 0)
                ret = -EINVAL;
out:
        return ret;
}
EXPORT_SYMBOL_GPL(xdr_process_buf);

/**
 * xdr_stream_decode_opaque - Decode variable length opaque
 * @xdr: pointer to xdr_stream
 * @ptr: location to store opaque data
 * @size: size of storage buffer @ptr
 *
 * Return values:
 *   On success, returns size of object stored in *@ptr
 *   %-EBADMSG on XDR buffer overflow
 *   %-EMSGSIZE on overflow of storage buffer @ptr
 */
ssize_t xdr_stream_decode_opaque(struct xdr_stream *xdr, void *ptr, size_t size)
{
        ssize_t ret;
        void *p;

        ret = xdr_stream_decode_opaque_inline(xdr, &p, size);
        if (ret <= 0)
                return ret;
        memcpy(ptr, p, ret);
        return ret;
}
EXPORT_SYMBOL_GPL(xdr_stream_decode_opaque);

/**
 * xdr_stream_decode_opaque_dup - Decode and duplicate variable length opaque
 * @xdr: pointer to xdr_stream
 * @ptr: location to store pointer to opaque data
 * @maxlen: maximum acceptable object size
 * @gfp_flags: GFP mask to use
 *
 * Return values:
 *   On success, returns size of object stored in *@ptr
 *   %-EBADMSG on XDR buffer overflow
 *   %-EMSGSIZE if the size of the object would exceed @maxlen
 *   %-ENOMEM on memory allocation failure
 */
ssize_t xdr_stream_decode_opaque_dup(struct xdr_stream *xdr, void **ptr,
                size_t maxlen, gfp_t gfp_flags)
{
        ssize_t ret;
        void *p;

        ret = xdr_stream_decode_opaque_inline(xdr, &p, maxlen);
        if (ret > 0) {
                *ptr = kmemdup(p, ret, gfp_flags);
                if (*ptr != NULL)
                        return ret;
                ret = -ENOMEM;
        }
        *ptr = NULL;
        return ret;
}
EXPORT_SYMBOL_GPL(xdr_stream_decode_opaque_dup);

/**
 * xdr_stream_decode_string - Decode variable length string
 * @xdr: pointer to xdr_stream
 * @str: location to store string
 * @size: size of storage buffer @str
 *
 * Return values:
 *   On success, returns length of NUL-terminated string stored in *@str
 *   %-EBADMSG on XDR buffer overflow
 *   %-EMSGSIZE on overflow of storage buffer @str
 */
ssize_t xdr_stream_decode_string(struct xdr_stream *xdr, char *str, size_t size)
{
        ssize_t ret;
        void *p;

        ret = xdr_stream_decode_opaque_inline(xdr, &p, size);
        if (ret > 0) {
                memcpy(str, p, ret);
                str[ret] = '\0';
                return strlen(str);
        }
        *str = '\0';
        return ret;
}
EXPORT_SYMBOL_GPL(xdr_stream_decode_string);

/**
 * xdr_stream_decode_string_dup - Decode and duplicate variable length string
 * @xdr: pointer to xdr_stream
 * @str: location to store pointer to string
 * @maxlen: maximum acceptable string length
 * @gfp_flags: GFP mask to use
 *
 * Return values:
 *   On success, returns length of NUL-terminated string stored in *@ptr
 *   %-EBADMSG on XDR buffer overflow
 *   %-EMSGSIZE if the size of the string would exceed @maxlen
 *   %-ENOMEM on memory allocation failure
 */
ssize_t xdr_stream_decode_string_dup(struct xdr_stream *xdr, char **str,
                size_t maxlen, gfp_t gfp_flags)
{
        void *p;
        ssize_t ret;

        ret = xdr_stream_decode_opaque_inline(xdr, &p, maxlen);
        if (ret > 0) {
                char *s = kmemdup_nul(p, ret, gfp_flags);
                if (s != NULL) {
                        *str = s;
                        return strlen(s);
                }
                ret = -ENOMEM;
        }
        *str = NULL;
        return ret;
}
EXPORT_SYMBOL_GPL(xdr_stream_decode_string_dup);