aio: don't include aio.h in sched.h

[mirror_ubuntu-zesty-kernel.git] / fs / ceph / file.c

#include <linux/ceph/ceph_debug.h>

#include <linux/module.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/file.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/writeback.h>
#include <linux/aio.h>

#include "super.h"
#include "mds_client.h"

/*
 * Ceph file operations
 *
 * Implement basic open/close functionality, and implement
 * read/write.
 *
 * We implement three modes of file I/O:
 *  - buffered uses the generic_file_aio_{read,write} helpers
 *
 *  - synchronous is used when there is multi-client read/write
 *    sharing, avoids the page cache, and synchronously waits for an
 *    ack from the OSD.
 *
 *  - direct io takes the variant of the sync path that references
 *    user pages directly.
 *
 * fsync() flushes and waits on dirty pages, but just queues metadata
 * for writeback: since the MDS can recover size and mtime there is no
 * need to wait for MDS acknowledgement.
 */


/*
 * Prepare an open request.  Preallocate ceph_cap to avoid an
 * inopportune ENOMEM later.
 */
static struct ceph_mds_request *
prepare_open_request(struct super_block *sb, int flags, int create_mode)
{
        struct ceph_fs_client *fsc = ceph_sb_to_client(sb);
        struct ceph_mds_client *mdsc = fsc->mdsc;
        struct ceph_mds_request *req;
        int want_auth = USE_ANY_MDS;
        int op = (flags & O_CREAT) ? CEPH_MDS_OP_CREATE : CEPH_MDS_OP_OPEN;

        if (flags & (O_WRONLY|O_RDWR|O_CREAT|O_TRUNC))
                want_auth = USE_AUTH_MDS;

        req = ceph_mdsc_create_request(mdsc, op, want_auth);
        if (IS_ERR(req))
                goto out;
        req->r_fmode = ceph_flags_to_mode(flags);
        req->r_args.open.flags = cpu_to_le32(flags);
        req->r_args.open.mode = cpu_to_le32(create_mode);
out:
        return req;
}

/*
 * initialize private struct file data.
 * if we fail, clean up by dropping fmode reference on the ceph_inode
 */
static int ceph_init_file(struct inode *inode, struct file *file, int fmode)
{
        struct ceph_file_info *cf;
        int ret = 0;

        switch (inode->i_mode & S_IFMT) {
        case S_IFREG:
        case S_IFDIR:
                dout("init_file %p %p 0%o (regular)\n", inode, file,
                     inode->i_mode);
                cf = kmem_cache_alloc(ceph_file_cachep, GFP_NOFS | __GFP_ZERO);
                if (cf == NULL) {
                        ceph_put_fmode(ceph_inode(inode), fmode); /* clean up */
                        return -ENOMEM;
                }
                cf->fmode = fmode;
                cf->next_offset = 2;
                file->private_data = cf;
                BUG_ON(inode->i_fop->release != ceph_release);
                break;

        case S_IFLNK:
                dout("init_file %p %p 0%o (symlink)\n", inode, file,
                     inode->i_mode);
                ceph_put_fmode(ceph_inode(inode), fmode); /* clean up */
                break;

        default:
                dout("init_file %p %p 0%o (special)\n", inode, file,
                     inode->i_mode);
                /*
                 * we need to drop the open ref now, since we don't
                 * have .release set to ceph_release.
                 */
                ceph_put_fmode(ceph_inode(inode), fmode); /* clean up */
                BUG_ON(inode->i_fop->release == ceph_release);

                /* call the proper open fop */
                ret = inode->i_fop->open(inode, file);
        }
        return ret;
}

/*
 * If we already have the requisite capabilities, we can satisfy
 * the open request locally (no need to request new caps from the
 * MDS).  We do, however, need to inform the MDS (asynchronously)
 * if our wanted caps set expands.
 */
int ceph_open(struct inode *inode, struct file *file)
{
        struct ceph_inode_info *ci = ceph_inode(inode);
        struct ceph_fs_client *fsc = ceph_sb_to_client(inode->i_sb);
        struct ceph_mds_client *mdsc = fsc->mdsc;
        struct ceph_mds_request *req;
        struct ceph_file_info *cf = file->private_data;
        struct inode *parent_inode = NULL;
        int err;
        int flags, fmode, wanted;

        if (cf) {
                dout("open file %p is already opened\n", file);
                return 0;
        }

        /* filter out O_CREAT|O_EXCL; vfs did that already.  yuck. */
        flags = file->f_flags & ~(O_CREAT|O_EXCL);
        if (S_ISDIR(inode->i_mode))
                flags = O_DIRECTORY;  /* mds likes to know */

        dout("open inode %p ino %llx.%llx file %p flags %d (%d)\n", inode,
             ceph_vinop(inode), file, flags, file->f_flags);
        fmode = ceph_flags_to_mode(flags);
        wanted = ceph_caps_for_mode(fmode);

        /* snapped files are read-only */
        if (ceph_snap(inode) != CEPH_NOSNAP && (file->f_mode & FMODE_WRITE))
                return -EROFS;

        /* trivially open snapdir */
        if (ceph_snap(inode) == CEPH_SNAPDIR) {
                spin_lock(&ci->i_ceph_lock);
                __ceph_get_fmode(ci, fmode);
                spin_unlock(&ci->i_ceph_lock);
                return ceph_init_file(inode, file, fmode);
        }

        /*
         * No need to block if we have caps on the auth MDS (for
         * write) or any MDS (for read).  Update wanted set
         * asynchronously.
         */
        spin_lock(&ci->i_ceph_lock);
        if (__ceph_is_any_real_caps(ci) &&
            (((fmode & CEPH_FILE_MODE_WR) == 0) || ci->i_auth_cap)) {
                int mds_wanted = __ceph_caps_mds_wanted(ci);
                int issued = __ceph_caps_issued(ci, NULL);

                dout("open %p fmode %d want %s issued %s using existing\n",
                     inode, fmode, ceph_cap_string(wanted),
                     ceph_cap_string(issued));
                __ceph_get_fmode(ci, fmode);
                spin_unlock(&ci->i_ceph_lock);

                /* adjust wanted? */
                if ((issued & wanted) != wanted &&
                    (mds_wanted & wanted) != wanted &&
                    ceph_snap(inode) != CEPH_SNAPDIR)
                        ceph_check_caps(ci, 0, NULL);

                return ceph_init_file(inode, file, fmode);
        } else if (ceph_snap(inode) != CEPH_NOSNAP &&
                   (ci->i_snap_caps & wanted) == wanted) {
                __ceph_get_fmode(ci, fmode);
                spin_unlock(&ci->i_ceph_lock);
                return ceph_init_file(inode, file, fmode);
        }
        spin_unlock(&ci->i_ceph_lock);

        dout("open fmode %d wants %s\n", fmode, ceph_cap_string(wanted));
        req = prepare_open_request(inode->i_sb, flags, 0);
        if (IS_ERR(req)) {
                err = PTR_ERR(req);
                goto out;
        }
        req->r_inode = inode;
        ihold(inode);
        req->r_num_caps = 1;
        if (flags & (O_CREAT|O_TRUNC))
                parent_inode = ceph_get_dentry_parent_inode(file->f_dentry);
        err = ceph_mdsc_do_request(mdsc, parent_inode, req);
        iput(parent_inode);
        if (!err)
                err = ceph_init_file(inode, file, req->r_fmode);
        ceph_mdsc_put_request(req);
        dout("open result=%d on %llx.%llx\n", err, ceph_vinop(inode));
out:
        return err;
}


/*
 * Do a lookup + open with a single request.  If we get a non-existent
 * file or symlink, return 1 so the VFS can retry.
 */
int ceph_atomic_open(struct inode *dir, struct dentry *dentry,
                     struct file *file, unsigned flags, umode_t mode,
                     int *opened)
{
        struct ceph_fs_client *fsc = ceph_sb_to_client(dir->i_sb);
        struct ceph_mds_client *mdsc = fsc->mdsc;
        struct ceph_mds_request *req;
        struct dentry *dn;
        int err;

        dout("atomic_open %p dentry %p '%.*s' %s flags %d mode 0%o\n",
             dir, dentry, dentry->d_name.len, dentry->d_name.name,
             d_unhashed(dentry) ? "unhashed" : "hashed", flags, mode);

        if (dentry->d_name.len > NAME_MAX)
                return -ENAMETOOLONG;

        err = ceph_init_dentry(dentry);
        if (err < 0)
                return err;

        /* do the open */
        req = prepare_open_request(dir->i_sb, flags, mode);
        if (IS_ERR(req))
                return PTR_ERR(req);
        req->r_dentry = dget(dentry);
        req->r_num_caps = 2;
        if (flags & O_CREAT) {
                req->r_dentry_drop = CEPH_CAP_FILE_SHARED;
                req->r_dentry_unless = CEPH_CAP_FILE_EXCL;
        }
        req->r_locked_dir = dir;           /* caller holds dir->i_mutex */
        err = ceph_mdsc_do_request(mdsc,
                                   (flags & (O_CREAT|O_TRUNC)) ? dir : NULL,
                                   req);
        if (err)
                goto out_err;

        err = ceph_handle_snapdir(req, dentry, err);
        if (err == 0 && (flags & O_CREAT) && !req->r_reply_info.head->is_dentry)
                err = ceph_handle_notrace_create(dir, dentry);

        if (d_unhashed(dentry)) {
                dn = ceph_finish_lookup(req, dentry, err);
                if (IS_ERR(dn))
                        err = PTR_ERR(dn);
        } else {
                /* we were given a hashed negative dentry */
                dn = NULL;
        }
        if (err)
                goto out_err;
        if (dn || dentry->d_inode == NULL || S_ISLNK(dentry->d_inode->i_mode)) {
                /* make vfs retry on splice, ENOENT, or symlink */
                dout("atomic_open finish_no_open on dn %p\n", dn);
                err = finish_no_open(file, dn);
        } else {
                dout("atomic_open finish_open on dn %p\n", dn);
                if (req->r_op == CEPH_MDS_OP_CREATE && req->r_reply_info.has_create_ino) {
                        *opened |= FILE_CREATED;
                }
                err = finish_open(file, dentry, ceph_open, opened);
        }

out_err:
        ceph_mdsc_put_request(req);
        dout("atomic_open result=%d\n", err);
        return err;
}

int ceph_release(struct inode *inode, struct file *file)
{
        struct ceph_inode_info *ci = ceph_inode(inode);
        struct ceph_file_info *cf = file->private_data;

        dout("release inode %p file %p\n", inode, file);
        ceph_put_fmode(ci, cf->fmode);
        if (cf->last_readdir)
                ceph_mdsc_put_request(cf->last_readdir);
        kfree(cf->last_name);
        kfree(cf->dir_info);
        dput(cf->dentry);
        kmem_cache_free(ceph_file_cachep, cf);

        /* wake up anyone waiting for caps on this inode */
        wake_up_all(&ci->i_cap_wq);
        return 0;
}

/*
 * Read a range of bytes striped over one or more objects.  Iterate over
 * objects we stripe over.  (That's not atomic, but good enough for now.)
 *
 * If we get a short result from the OSD, check against i_size; we need to
 * only return a short read to the caller if we hit EOF.
 */
static int striped_read(struct inode *inode,
                        u64 off, u64 len,
                        struct page **pages, int num_pages,
                        int *checkeof, bool o_direct,
                        unsigned long buf_align)
{
        struct ceph_fs_client *fsc = ceph_inode_to_client(inode);
        struct ceph_inode_info *ci = ceph_inode(inode);
        u64 pos, this_len;
        int io_align, page_align;
        int left, pages_left;
        int read;
        struct page **page_pos;
        int ret;
        bool hit_stripe, was_short;

        /*
         * we may need to do multiple reads.  not atomic, unfortunately.
         */
        pos = off;
        left = len;
        page_pos = pages;
        pages_left = num_pages;
        read = 0;
        io_align = off & ~PAGE_MASK;

more:
        if (o_direct)
                page_align = (pos - io_align + buf_align) & ~PAGE_MASK;
        else
                page_align = pos & ~PAGE_MASK;
        this_len = left;
        ret = ceph_osdc_readpages(&fsc->client->osdc, ceph_vino(inode),
                                  &ci->i_layout, pos, &this_len,
                                  ci->i_truncate_seq,
                                  ci->i_truncate_size,
                                  page_pos, pages_left, page_align);
        if (ret == -ENOENT)
                ret = 0;
        hit_stripe = this_len < left;
        was_short = ret >= 0 && ret < this_len;
        dout("striped_read %llu~%u (read %u) got %d%s%s\n", pos, left, read,
             ret, hit_stripe ? " HITSTRIPE" : "", was_short ? " SHORT" : "");

        if (ret > 0) {
                int didpages = (page_align + ret) >> PAGE_CACHE_SHIFT;

                if (read < pos - off) {
                        dout(" zero gap %llu to %llu\n", off + read, pos);
                        ceph_zero_page_vector_range(page_align + read,
                                                    pos - off - read, pages);
                }
                pos += ret;
                read = pos - off;
                left -= ret;
                page_pos += didpages;
                pages_left -= didpages;

                /* hit stripe? */
                if (left && hit_stripe)
                        goto more;
        }

        if (was_short) {
                /* did we bounce off eof? */
                if (pos + left > inode->i_size)
                        *checkeof = 1;

                /* zero trailing bytes (inside i_size) */
                if (left > 0 && pos < inode->i_size) {
                        if (pos + left > inode->i_size)
                                left = inode->i_size - pos;

                        dout("zero tail %d\n", left);
                        ceph_zero_page_vector_range(page_align + read, left,
                                                    pages);
                        read += left;
                }
        }

        if (ret >= 0)
                ret = read;
        dout("striped_read returns %d\n", ret);
        return ret;
}

/*
 * Completely synchronous read and write methods.  Direct from __user
 * buffer to osd, or directly to user pages (if O_DIRECT).
 *
 * If the read spans object boundary, just do multiple reads.
 */
static ssize_t ceph_sync_read(struct file *file, char __user *data,
                              unsigned len, loff_t *poff, int *checkeof)
{
        struct inode *inode = file_inode(file);
        struct page **pages;
        u64 off = *poff;
        int num_pages, ret;

        dout("sync_read on file %p %llu~%u %s\n", file, off, len,
             (file->f_flags & O_DIRECT) ? "O_DIRECT" : "");

        if (file->f_flags & O_DIRECT) {
                num_pages = calc_pages_for((unsigned long)data, len);
                pages = ceph_get_direct_page_vector(data, num_pages, true);
        } else {
                num_pages = calc_pages_for(off, len);
                pages = ceph_alloc_page_vector(num_pages, GFP_NOFS);
        }
        if (IS_ERR(pages))
                return PTR_ERR(pages);

        /*
         * flush any page cache pages in this range.  this
         * will make concurrent normal and sync io slow,
         * but it will at least behave sensibly when they are
         * in sequence.
         */
        ret = filemap_write_and_wait(inode->i_mapping);
        if (ret < 0)
                goto done;

        ret = striped_read(inode, off, len, pages, num_pages, checkeof,
                           file->f_flags & O_DIRECT,
                           (unsigned long)data & ~PAGE_MASK);

        if (ret >= 0 && (file->f_flags & O_DIRECT) == 0)
                ret = ceph_copy_page_vector_to_user(pages, data, off, ret);
        if (ret >= 0)
                *poff = off + ret;

done:
        if (file->f_flags & O_DIRECT)
                ceph_put_page_vector(pages, num_pages, true);
        else
                ceph_release_page_vector(pages, num_pages);
        dout("sync_read result %d\n", ret);
        return ret;
}

/*
 * Write commit request unsafe callback, called to tell us when a
 * request is unsafe (that is, in flight--has been handed to the
 * messenger to send to its target osd).  It is called again when
 * we've received a response message indicating the request is
 * "safe" (its CEPH_OSD_FLAG_ONDISK flag is set), or when a request
 * is completed early (and unsuccessfully) due to a timeout or
 * interrupt.
 *
 * This is used if we requested both an ACK and ONDISK commit reply
 * from the OSD.
 */
static void ceph_sync_write_unsafe(struct ceph_osd_request *req, bool unsafe)
{
        struct ceph_inode_info *ci = ceph_inode(req->r_inode);

        dout("%s %p tid %llu %ssafe\n", __func__, req, req->r_tid,
                unsafe ? "un" : "");
        if (unsafe) {
                ceph_get_cap_refs(ci, CEPH_CAP_FILE_WR);
                spin_lock(&ci->i_unsafe_lock);
                list_add_tail(&req->r_unsafe_item,
                              &ci->i_unsafe_writes);
                spin_unlock(&ci->i_unsafe_lock);
        } else {
                spin_lock(&ci->i_unsafe_lock);
                list_del_init(&req->r_unsafe_item);
                spin_unlock(&ci->i_unsafe_lock);
                ceph_put_cap_refs(ci, CEPH_CAP_FILE_WR);
        }
}

/*
 * Synchronous write, straight from __user pointer or user pages (if
 * O_DIRECT).
 *
 * If write spans object boundary, just do multiple writes.  (For a
 * correct atomic write, we should e.g. take write locks on all
 * objects, rollback on failure, etc.)
 */
static ssize_t ceph_sync_write(struct file *file, const char __user *data,
                               size_t left, loff_t pos, loff_t *ppos)
{
        struct inode *inode = file_inode(file);
        struct ceph_inode_info *ci = ceph_inode(inode);
        struct ceph_fs_client *fsc = ceph_inode_to_client(inode);
        struct ceph_snap_context *snapc;
        struct ceph_vino vino;
        struct ceph_osd_request *req;
        int num_ops = 1;
        struct page **pages;
        int num_pages;
        u64 len;
        int written = 0;
        int flags;
        int check_caps = 0;
        int page_align, io_align;
        unsigned long buf_align;
        int ret;
        struct timespec mtime = CURRENT_TIME;
        bool own_pages = false;

        if (ceph_snap(file_inode(file)) != CEPH_NOSNAP)
                return -EROFS;

        dout("sync_write on file %p %lld~%u %s\n", file, pos,
             (unsigned)left, (file->f_flags & O_DIRECT) ? "O_DIRECT" : "");

        ret = filemap_write_and_wait_range(inode->i_mapping, pos, pos + left);
        if (ret < 0)
                return ret;

        ret = invalidate_inode_pages2_range(inode->i_mapping,
                                            pos >> PAGE_CACHE_SHIFT,
                                            (pos + left) >> PAGE_CACHE_SHIFT);
        if (ret < 0)
                dout("invalidate_inode_pages2_range returned %d\n", ret);

        flags = CEPH_OSD_FLAG_ORDERSNAP |
                CEPH_OSD_FLAG_ONDISK |
                CEPH_OSD_FLAG_WRITE;
        if ((file->f_flags & (O_SYNC|O_DIRECT)) == 0)
                flags |= CEPH_OSD_FLAG_ACK;
        else
                num_ops++;      /* Also include a 'startsync' command. */

        /*
         * we may need to do multiple writes here if we span an object
         * boundary.  this isn't atomic, unfortunately.  :(
         */
more:
        io_align = pos & ~PAGE_MASK;
        buf_align = (unsigned long)data & ~PAGE_MASK;
        len = left;

        snapc = ci->i_snap_realm->cached_context;
        vino = ceph_vino(inode);
        req = ceph_osdc_new_request(&fsc->client->osdc, &ci->i_layout,
                                    vino, pos, &len, num_ops,
                                    CEPH_OSD_OP_WRITE, flags, snapc,
                                    ci->i_truncate_seq, ci->i_truncate_size,
                                    false);
        if (IS_ERR(req))
                return PTR_ERR(req);

        /* write from beginning of first page, regardless of io alignment */
        page_align = file->f_flags & O_DIRECT ? buf_align : io_align;
        num_pages = calc_pages_for(page_align, len);
        if (file->f_flags & O_DIRECT) {
                pages = ceph_get_direct_page_vector(data, num_pages, false);
                if (IS_ERR(pages)) {
                        ret = PTR_ERR(pages);
                        goto out;
                }

                /*
                 * throw out any page cache pages in this range. this
                 * may block.
                 */
                truncate_inode_pages_range(inode->i_mapping, pos,
                                           (pos+len) | (PAGE_CACHE_SIZE-1));
        } else {
                pages = ceph_alloc_page_vector(num_pages, GFP_NOFS);
                if (IS_ERR(pages)) {
                        ret = PTR_ERR(pages);
                        goto out;
                }
                ret = ceph_copy_user_to_page_vector(pages, data, pos, len);
                if (ret < 0) {
                        ceph_release_page_vector(pages, num_pages);
                        goto out;
                }

                if ((file->f_flags & O_SYNC) == 0) {
                        /* get a second commit callback */
                        req->r_unsafe_callback = ceph_sync_write_unsafe;
                        req->r_inode = inode;
                        own_pages = true;
                }
        }
        osd_req_op_extent_osd_data_pages(req, 0, pages, len, page_align,
                                        false, own_pages);

        /* BUG_ON(vino.snap != CEPH_NOSNAP); */
        ceph_osdc_build_request(req, pos, snapc, vino.snap, &mtime);

        ret = ceph_osdc_start_request(&fsc->client->osdc, req, false);
        if (!ret)
                ret = ceph_osdc_wait_request(&fsc->client->osdc, req);

        if (file->f_flags & O_DIRECT)
                ceph_put_page_vector(pages, num_pages, false);
        else if (file->f_flags & O_SYNC)
                ceph_release_page_vector(pages, num_pages);

out:
        ceph_osdc_put_request(req);
        if (ret == 0) {
                pos += len;
                written += len;
                left -= len;
                data += len;
                if (left)
                        goto more;

                ret = written;
                *ppos = pos;
                if (pos > i_size_read(inode))
                        check_caps = ceph_inode_set_size(inode, pos);
                if (check_caps)
                        ceph_check_caps(ceph_inode(inode), CHECK_CAPS_AUTHONLY,
                                        NULL);
        }
        return ret;
}

/*
 * Wrap generic_file_aio_read with checks for cap bits on the inode.
 * Atomically grab references, so that those bits are not released
 * back to the MDS mid-read.
 *
 * Hmm, the sync read case isn't actually async... should it be?
 */
static ssize_t ceph_aio_read(struct kiocb *iocb, const struct iovec *iov,
                             unsigned long nr_segs, loff_t pos)
{
        struct file *filp = iocb->ki_filp;
        struct ceph_file_info *fi = filp->private_data;
        loff_t *ppos = &iocb->ki_pos;
        size_t len = iov->iov_len;
        struct inode *inode = file_inode(filp);
        struct ceph_inode_info *ci = ceph_inode(inode);
        void __user *base = iov->iov_base;
        ssize_t ret;
        int want, got = 0;
        int checkeof = 0, read = 0;

        dout("aio_read %p %llx.%llx %llu~%u trying to get caps on %p\n",
             inode, ceph_vinop(inode), pos, (unsigned)len, inode);
again:
        if (fi->fmode & CEPH_FILE_MODE_LAZY)
                want = CEPH_CAP_FILE_CACHE | CEPH_CAP_FILE_LAZYIO;
        else
                want = CEPH_CAP_FILE_CACHE;
        ret = ceph_get_caps(ci, CEPH_CAP_FILE_RD, want, &got, -1);
        if (ret < 0)
                goto out;
        dout("aio_read %p %llx.%llx %llu~%u got cap refs on %s\n",
             inode, ceph_vinop(inode), pos, (unsigned)len,
             ceph_cap_string(got));

        if ((got & (CEPH_CAP_FILE_CACHE|CEPH_CAP_FILE_LAZYIO)) == 0 ||
            (iocb->ki_filp->f_flags & O_DIRECT) ||
            (inode->i_sb->s_flags & MS_SYNCHRONOUS) ||
            (fi->flags & CEPH_F_SYNC))
                /* hmm, this isn't really async... */
                ret = ceph_sync_read(filp, base, len, ppos, &checkeof);
        else
                ret = generic_file_aio_read(iocb, iov, nr_segs, pos);

out:
        dout("aio_read %p %llx.%llx dropping cap refs on %s = %d\n",
             inode, ceph_vinop(inode), ceph_cap_string(got), (int)ret);
        ceph_put_cap_refs(ci, got);

        if (checkeof && ret >= 0) {
                int statret = ceph_do_getattr(inode, CEPH_STAT_CAP_SIZE);

                /* hit EOF or hole? */
                if (statret == 0 && *ppos < inode->i_size) {
                        dout("aio_read sync_read hit hole, ppos %lld < size %lld, reading more\n", *ppos, inode->i_size);
                        read += ret;
                        base += ret;
                        len -= ret;
                        checkeof = 0;
                        goto again;
                }
        }
        if (ret >= 0)
                ret += read;

        return ret;
}

/*
 * Take cap references to avoid releasing caps to MDS mid-write.
 *
 * If we are synchronous, and write with an old snap context, the OSD
 * may return EOLDSNAPC.  In that case, retry the write.. _after_
 * dropping our cap refs and allowing the pending snap to logically
 * complete _before_ this write occurs.
 *
 * If we are near ENOSPC, write synchronously.
 */
static ssize_t ceph_aio_write(struct kiocb *iocb, const struct iovec *iov,
                       unsigned long nr_segs, loff_t pos)
{
        struct file *file = iocb->ki_filp;
        struct ceph_file_info *fi = file->private_data;
        struct inode *inode = file_inode(file);
        struct ceph_inode_info *ci = ceph_inode(inode);
        struct ceph_osd_client *osdc =
                &ceph_sb_to_client(inode->i_sb)->client->osdc;
        ssize_t count, written = 0;
        int err, want, got;
        bool hold_mutex;

        if (ceph_snap(inode) != CEPH_NOSNAP)
                return -EROFS;

        sb_start_write(inode->i_sb);
        mutex_lock(&inode->i_mutex);
        hold_mutex = true;

        err = generic_segment_checks(iov, &nr_segs, &count, VERIFY_READ);
        if (err)
                goto out;

        /* We can write back this queue in page reclaim */
        current->backing_dev_info = file->f_mapping->backing_dev_info;

        err = generic_write_checks(file, &pos, &count, S_ISBLK(inode->i_mode));
        if (err)
                goto out;

        if (count == 0)
                goto out;

        err = file_remove_suid(file);
        if (err)
                goto out;

        err = file_update_time(file);
        if (err)
                goto out;

retry_snap:
        if (ceph_osdmap_flag(osdc->osdmap, CEPH_OSDMAP_FULL)) {
                err = -ENOSPC;
                goto out;
        }

        dout("aio_write %p %llx.%llx %llu~%zd getting caps. i_size %llu\n",
             inode, ceph_vinop(inode), pos, count, inode->i_size);
        if (fi->fmode & CEPH_FILE_MODE_LAZY)
                want = CEPH_CAP_FILE_BUFFER | CEPH_CAP_FILE_LAZYIO;
        else
                want = CEPH_CAP_FILE_BUFFER;
        got = 0;
        err = ceph_get_caps(ci, CEPH_CAP_FILE_WR, want, &got, pos + count);
        if (err < 0)
                goto out;

        dout("aio_write %p %llx.%llx %llu~%zd got cap refs on %s\n",
             inode, ceph_vinop(inode), pos, count, ceph_cap_string(got));

        if ((got & (CEPH_CAP_FILE_BUFFER|CEPH_CAP_FILE_LAZYIO)) == 0 ||
            (iocb->ki_filp->f_flags & O_DIRECT) ||
            (inode->i_sb->s_flags & MS_SYNCHRONOUS) ||
            (fi->flags & CEPH_F_SYNC)) {
                mutex_unlock(&inode->i_mutex);
                written = ceph_sync_write(file, iov->iov_base, count,
                                          pos, &iocb->ki_pos);
        } else {
                written = generic_file_buffered_write(iocb, iov, nr_segs,
                                                      pos, &iocb->ki_pos,
                                                      count, 0);
                mutex_unlock(&inode->i_mutex);
        }
        hold_mutex = false;

        if (written >= 0) {
                int dirty;
                spin_lock(&ci->i_ceph_lock);
                dirty = __ceph_mark_dirty_caps(ci, CEPH_CAP_FILE_WR);
                spin_unlock(&ci->i_ceph_lock);
                if (dirty)
                        __mark_inode_dirty(inode, dirty);
        }

        dout("aio_write %p %llx.%llx %llu~%u  dropping cap refs on %s\n",
             inode, ceph_vinop(inode), pos, (unsigned)iov->iov_len,
             ceph_cap_string(got));
        ceph_put_cap_refs(ci, got);

        if (written >= 0 &&
            ((file->f_flags & O_SYNC) || IS_SYNC(file->f_mapping->host) ||
             ceph_osdmap_flag(osdc->osdmap, CEPH_OSDMAP_NEARFULL))) {
                err = vfs_fsync_range(file, pos, pos + written - 1, 1);
                if (err < 0)
                        written = err;
        }

        if (written == -EOLDSNAPC) {
                dout("aio_write %p %llx.%llx %llu~%u got EOLDSNAPC, retrying\n",
                     inode, ceph_vinop(inode), pos, (unsigned)iov->iov_len);
                mutex_lock(&inode->i_mutex);
                hold_mutex = true;
                goto retry_snap;
        }
out:
        if (hold_mutex)
                mutex_unlock(&inode->i_mutex);
        sb_end_write(inode->i_sb);
        current->backing_dev_info = NULL;

        return written ? written : err;
}

/*
 * llseek.  be sure to verify file size on SEEK_END.
 */
static loff_t ceph_llseek(struct file *file, loff_t offset, int whence)
{
        struct inode *inode = file->f_mapping->host;
        int ret;

        mutex_lock(&inode->i_mutex);
        __ceph_do_pending_vmtruncate(inode, false);

        if (whence == SEEK_END || whence == SEEK_DATA || whence == SEEK_HOLE) {
                ret = ceph_do_getattr(inode, CEPH_STAT_CAP_SIZE);
                if (ret < 0) {
                        offset = ret;
                        goto out;
                }
        }

        switch (whence) {
        case SEEK_END:
                offset += inode->i_size;
                break;
        case SEEK_CUR:
                /*
                 * Here we special-case the lseek(fd, 0, SEEK_CUR)
                 * position-querying operation.  Avoid rewriting the "same"
                 * f_pos value back to the file because a concurrent read(),
                 * write() or lseek() might have altered it
                 */
                if (offset == 0) {
                        offset = file->f_pos;
                        goto out;
                }
                offset += file->f_pos;
                break;
        case SEEK_DATA:
                if (offset >= inode->i_size) {
                        ret = -ENXIO;
                        goto out;
                }
                break;
        case SEEK_HOLE:
                if (offset >= inode->i_size) {
                        ret = -ENXIO;
                        goto out;
                }
                offset = inode->i_size;
                break;
        }

        if (offset < 0 || offset > inode->i_sb->s_maxbytes) {
                offset = -EINVAL;
                goto out;
        }

        /* Special lock needed here? */
        if (offset != file->f_pos) {
                file->f_pos = offset;
                file->f_version = 0;
        }

out:
        mutex_unlock(&inode->i_mutex);
        return offset;
}

const struct file_operations ceph_file_fops = {
        .open = ceph_open,
        .release = ceph_release,
        .llseek = ceph_llseek,
        .read = do_sync_read,
        .write = do_sync_write,
        .aio_read = ceph_aio_read,
        .aio_write = ceph_aio_write,
        .mmap = ceph_mmap,
        .fsync = ceph_fsync,
        .lock = ceph_lock,
        .flock = ceph_flock,
        .splice_read = generic_file_splice_read,
        .splice_write = generic_file_splice_write,
        .unlocked_ioctl = ceph_ioctl,
        .compat_ioctl   = ceph_ioctl,
};