Support idmapped mount

[mirror_zfs.git] / module / zfs / zfs_vnops.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or https://opensource.org/licenses/CDDL-1.0.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright (c) 2012, 2018 by Delphix. All rights reserved.
 * Copyright (c) 2015 by Chunwei Chen. All rights reserved.
 * Copyright 2017 Nexenta Systems, Inc.
 */

/* Portions Copyright 2007 Jeremy Teo */
/* Portions Copyright 2010 Robert Milkowski */

#include <sys/types.h>
#include <sys/param.h>
#include <sys/time.h>
#include <sys/sysmacros.h>
#include <sys/vfs.h>
#include <sys/uio_impl.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <sys/kmem.h>
#include <sys/cmn_err.h>
#include <sys/errno.h>
#include <sys/zfs_dir.h>
#include <sys/zfs_acl.h>
#include <sys/zfs_ioctl.h>
#include <sys/fs/zfs.h>
#include <sys/dmu.h>
#include <sys/dmu_objset.h>
#include <sys/spa.h>
#include <sys/txg.h>
#include <sys/dbuf.h>
#include <sys/policy.h>
#include <sys/zfs_vnops.h>
#include <sys/zfs_quota.h>
#include <sys/zfs_vfsops.h>
#include <sys/zfs_znode.h>


static ulong_t zfs_fsync_sync_cnt = 4;

int
zfs_fsync(znode_t *zp, int syncflag, cred_t *cr)
{
        int error = 0;
        zfsvfs_t *zfsvfs = ZTOZSB(zp);

        (void) tsd_set(zfs_fsyncer_key, (void *)zfs_fsync_sync_cnt);

        if (zfsvfs->z_os->os_sync != ZFS_SYNC_DISABLED) {
                if ((error = zfs_enter_verify_zp(zfsvfs, zp, FTAG)) != 0)
                        goto out;
                atomic_inc_32(&zp->z_sync_writes_cnt);
                zil_commit(zfsvfs->z_log, zp->z_id);
                atomic_dec_32(&zp->z_sync_writes_cnt);
                zfs_exit(zfsvfs, FTAG);
        }
out:
        tsd_set(zfs_fsyncer_key, NULL);

        return (error);
}


#if defined(SEEK_HOLE) && defined(SEEK_DATA)
/*
 * Lseek support for finding holes (cmd == SEEK_HOLE) and
 * data (cmd == SEEK_DATA). "off" is an in/out parameter.
 */
static int
zfs_holey_common(znode_t *zp, ulong_t cmd, loff_t *off)
{
        zfs_locked_range_t *lr;
        uint64_t noff = (uint64_t)*off; /* new offset */
        uint64_t file_sz;
        int error;
        boolean_t hole;

        file_sz = zp->z_size;
        if (noff >= file_sz)  {
                return (SET_ERROR(ENXIO));
        }

        if (cmd == F_SEEK_HOLE)
                hole = B_TRUE;
        else
                hole = B_FALSE;

        /* Flush any mmap()'d data to disk */
        if (zn_has_cached_data(zp))
                zn_flush_cached_data(zp, B_FALSE);

        lr = zfs_rangelock_enter(&zp->z_rangelock, 0, file_sz, RL_READER);
        error = dmu_offset_next(ZTOZSB(zp)->z_os, zp->z_id, hole, &noff);
        zfs_rangelock_exit(lr);

        if (error == ESRCH)
                return (SET_ERROR(ENXIO));

        /* File was dirty, so fall back to using generic logic */
        if (error == EBUSY) {
                if (hole)
                        *off = file_sz;

                return (0);
        }

        /*
         * We could find a hole that begins after the logical end-of-file,
         * because dmu_offset_next() only works on whole blocks.  If the
         * EOF falls mid-block, then indicate that the "virtual hole"
         * at the end of the file begins at the logical EOF, rather than
         * at the end of the last block.
         */
        if (noff > file_sz) {
                ASSERT(hole);
                noff = file_sz;
        }

        if (noff < *off)
                return (error);
        *off = noff;
        return (error);
}

int
zfs_holey(znode_t *zp, ulong_t cmd, loff_t *off)
{
        zfsvfs_t *zfsvfs = ZTOZSB(zp);
        int error;

        if ((error = zfs_enter_verify_zp(zfsvfs, zp, FTAG)) != 0)
                return (error);

        error = zfs_holey_common(zp, cmd, off);

        zfs_exit(zfsvfs, FTAG);
        return (error);
}
#endif /* SEEK_HOLE && SEEK_DATA */

int
zfs_access(znode_t *zp, int mode, int flag, cred_t *cr)
{
        zfsvfs_t *zfsvfs = ZTOZSB(zp);
        int error;

        if ((error = zfs_enter_verify_zp(zfsvfs, zp, FTAG)) != 0)
                return (error);

        if (flag & V_ACE_MASK)
                error = zfs_zaccess(zp, mode, flag, B_FALSE, cr, NULL);
        else
                error = zfs_zaccess_rwx(zp, mode, flag, cr, NULL);

        zfs_exit(zfsvfs, FTAG);
        return (error);
}

static uint64_t zfs_vnops_read_chunk_size = 1024 * 1024; /* Tunable */

/*
 * Read bytes from specified file into supplied buffer.
 *
 *      IN:     zp      - inode of file to be read from.
 *              uio     - structure supplying read location, range info,
 *                        and return buffer.
 *              ioflag  - O_SYNC flags; used to provide FRSYNC semantics.
 *                        O_DIRECT flag; used to bypass page cache.
 *              cr      - credentials of caller.
 *
 *      OUT:    uio     - updated offset and range, buffer filled.
 *
 *      RETURN: 0 on success, error code on failure.
 *
 * Side Effects:
 *      inode - atime updated if byte count > 0
 */
int
zfs_read(struct znode *zp, zfs_uio_t *uio, int ioflag, cred_t *cr)
{
        (void) cr;
        int error = 0;
        boolean_t frsync = B_FALSE;

        zfsvfs_t *zfsvfs = ZTOZSB(zp);
        if ((error = zfs_enter_verify_zp(zfsvfs, zp, FTAG)) != 0)
                return (error);

        if (zp->z_pflags & ZFS_AV_QUARANTINED) {
                zfs_exit(zfsvfs, FTAG);
                return (SET_ERROR(EACCES));
        }

        /* We don't copy out anything useful for directories. */
        if (Z_ISDIR(ZTOTYPE(zp))) {
                zfs_exit(zfsvfs, FTAG);
                return (SET_ERROR(EISDIR));
        }

        /*
         * Validate file offset
         */
        if (zfs_uio_offset(uio) < (offset_t)0) {
                zfs_exit(zfsvfs, FTAG);
                return (SET_ERROR(EINVAL));
        }

        /*
         * Fasttrack empty reads
         */
        if (zfs_uio_resid(uio) == 0) {
                zfs_exit(zfsvfs, FTAG);
                return (0);
        }

#ifdef FRSYNC
        /*
         * If we're in FRSYNC mode, sync out this znode before reading it.
         * Only do this for non-snapshots.
         *
         * Some platforms do not support FRSYNC and instead map it
         * to O_SYNC, which results in unnecessary calls to zil_commit. We
         * only honor FRSYNC requests on platforms which support it.
         */
        frsync = !!(ioflag & FRSYNC);
#endif
        if (zfsvfs->z_log &&
            (frsync || zfsvfs->z_os->os_sync == ZFS_SYNC_ALWAYS))
                zil_commit(zfsvfs->z_log, zp->z_id);

        /*
         * Lock the range against changes.
         */
        zfs_locked_range_t *lr = zfs_rangelock_enter(&zp->z_rangelock,
            zfs_uio_offset(uio), zfs_uio_resid(uio), RL_READER);

        /*
         * If we are reading past end-of-file we can skip
         * to the end; but we might still need to set atime.
         */
        if (zfs_uio_offset(uio) >= zp->z_size) {
                error = 0;
                goto out;
        }

        ASSERT(zfs_uio_offset(uio) < zp->z_size);
#if defined(__linux__)
        ssize_t start_offset = zfs_uio_offset(uio);
#endif
        ssize_t n = MIN(zfs_uio_resid(uio), zp->z_size - zfs_uio_offset(uio));
        ssize_t start_resid = n;

        while (n > 0) {
                ssize_t nbytes = MIN(n, zfs_vnops_read_chunk_size -
                    P2PHASE(zfs_uio_offset(uio), zfs_vnops_read_chunk_size));
#ifdef UIO_NOCOPY
                if (zfs_uio_segflg(uio) == UIO_NOCOPY)
                        error = mappedread_sf(zp, nbytes, uio);
                else
#endif
                if (zn_has_cached_data(zp) && !(ioflag & O_DIRECT)) {
                        error = mappedread(zp, nbytes, uio);
                } else {
                        error = dmu_read_uio_dbuf(sa_get_db(zp->z_sa_hdl),
                            uio, nbytes);
                }

                if (error) {
                        /* convert checksum errors into IO errors */
                        if (error == ECKSUM)
                                error = SET_ERROR(EIO);

#if defined(__linux__)
                        /*
                         * if we actually read some bytes, bubbling EFAULT
                         * up to become EAGAIN isn't what we want here...
                         *
                         * ...on Linux, at least. On FBSD, doing this breaks.
                         */
                        if (error == EFAULT &&
                            (zfs_uio_offset(uio) - start_offset) != 0)
                                error = 0;
#endif
                        break;
                }

                n -= nbytes;
        }

        int64_t nread = start_resid - n;
        dataset_kstats_update_read_kstats(&zfsvfs->z_kstat, nread);
        task_io_account_read(nread);
out:
        zfs_rangelock_exit(lr);

        ZFS_ACCESSTIME_STAMP(zfsvfs, zp);
        zfs_exit(zfsvfs, FTAG);
        return (error);
}

static void
zfs_clear_setid_bits_if_necessary(zfsvfs_t *zfsvfs, znode_t *zp, cred_t *cr,
    uint64_t *clear_setid_bits_txgp, dmu_tx_t *tx)
{
        zilog_t *zilog = zfsvfs->z_log;
        const uint64_t uid = KUID_TO_SUID(ZTOUID(zp));

        ASSERT(clear_setid_bits_txgp != NULL);
        ASSERT(tx != NULL);

        /*
         * Clear Set-UID/Set-GID bits on successful write if not
         * privileged and at least one of the execute bits is set.
         *
         * It would be nice to do this after all writes have
         * been done, but that would still expose the ISUID/ISGID
         * to another app after the partial write is committed.
         *
         * Note: we don't call zfs_fuid_map_id() here because
         * user 0 is not an ephemeral uid.
         */
        mutex_enter(&zp->z_acl_lock);
        if ((zp->z_mode & (S_IXUSR | (S_IXUSR >> 3) | (S_IXUSR >> 6))) != 0 &&
            (zp->z_mode & (S_ISUID | S_ISGID)) != 0 &&
            secpolicy_vnode_setid_retain(zp, cr,
            ((zp->z_mode & S_ISUID) != 0 && uid == 0)) != 0) {
                uint64_t newmode;

                zp->z_mode &= ~(S_ISUID | S_ISGID);
                newmode = zp->z_mode;
                (void) sa_update(zp->z_sa_hdl, SA_ZPL_MODE(zfsvfs),
                    (void *)&newmode, sizeof (uint64_t), tx);

                mutex_exit(&zp->z_acl_lock);

                /*
                 * Make sure SUID/SGID bits will be removed when we replay the
                 * log. If the setid bits are keep coming back, don't log more
                 * than one TX_SETATTR per transaction group.
                 */
                if (*clear_setid_bits_txgp != dmu_tx_get_txg(tx)) {
                        vattr_t va = {0};

                        va.va_mask = ATTR_MODE;
                        va.va_nodeid = zp->z_id;
                        va.va_mode = newmode;
                        zfs_log_setattr(zilog, tx, TX_SETATTR, zp, &va,
                            ATTR_MODE, NULL);
                        *clear_setid_bits_txgp = dmu_tx_get_txg(tx);
                }
        } else {
                mutex_exit(&zp->z_acl_lock);
        }
}

/*
 * Write the bytes to a file.
 *
 *      IN:     zp      - znode of file to be written to.
 *              uio     - structure supplying write location, range info,
 *                        and data buffer.
 *              ioflag  - O_APPEND flag set if in append mode.
 *                        O_DIRECT flag; used to bypass page cache.
 *              cr      - credentials of caller.
 *
 *      OUT:    uio     - updated offset and range.
 *
 *      RETURN: 0 if success
 *              error code if failure
 *
 * Timestamps:
 *      ip - ctime|mtime updated if byte count > 0
 */
int
zfs_write(znode_t *zp, zfs_uio_t *uio, int ioflag, cred_t *cr)
{
        int error = 0, error1;
        ssize_t start_resid = zfs_uio_resid(uio);
        uint64_t clear_setid_bits_txg = 0;

        /*
         * Fasttrack empty write
         */
        ssize_t n = start_resid;
        if (n == 0)
                return (0);

        zfsvfs_t *zfsvfs = ZTOZSB(zp);
        if ((error = zfs_enter_verify_zp(zfsvfs, zp, FTAG)) != 0)
                return (error);

        sa_bulk_attr_t bulk[4];
        int count = 0;
        uint64_t mtime[2], ctime[2];
        SA_ADD_BULK_ATTR(bulk, count, SA_ZPL_MTIME(zfsvfs), NULL, &mtime, 16);
        SA_ADD_BULK_ATTR(bulk, count, SA_ZPL_CTIME(zfsvfs), NULL, &ctime, 16);
        SA_ADD_BULK_ATTR(bulk, count, SA_ZPL_SIZE(zfsvfs), NULL,
            &zp->z_size, 8);
        SA_ADD_BULK_ATTR(bulk, count, SA_ZPL_FLAGS(zfsvfs), NULL,
            &zp->z_pflags, 8);

        /*
         * Callers might not be able to detect properly that we are read-only,
         * so check it explicitly here.
         */
        if (zfs_is_readonly(zfsvfs)) {
                zfs_exit(zfsvfs, FTAG);
                return (SET_ERROR(EROFS));
        }

        /*
         * If immutable or not appending then return EPERM.
         * Intentionally allow ZFS_READONLY through here.
         * See zfs_zaccess_common()
         */
        if ((zp->z_pflags & ZFS_IMMUTABLE) ||
            ((zp->z_pflags & ZFS_APPENDONLY) && !(ioflag & O_APPEND) &&
            (zfs_uio_offset(uio) < zp->z_size))) {
                zfs_exit(zfsvfs, FTAG);
                return (SET_ERROR(EPERM));
        }

        /*
         * Validate file offset
         */
        offset_t woff = ioflag & O_APPEND ? zp->z_size : zfs_uio_offset(uio);
        if (woff < 0) {
                zfs_exit(zfsvfs, FTAG);
                return (SET_ERROR(EINVAL));
        }

        const uint64_t max_blksz = zfsvfs->z_max_blksz;

        /*
         * Pre-fault the pages to ensure slow (eg NFS) pages
         * don't hold up txg.
         * Skip this if uio contains loaned arc_buf.
         */
        if (zfs_uio_prefaultpages(MIN(n, max_blksz), uio)) {
                zfs_exit(zfsvfs, FTAG);
                return (SET_ERROR(EFAULT));
        }

        /*
         * If in append mode, set the io offset pointer to eof.
         */
        zfs_locked_range_t *lr;
        if (ioflag & O_APPEND) {
                /*
                 * Obtain an appending range lock to guarantee file append
                 * semantics.  We reset the write offset once we have the lock.
                 */
                lr = zfs_rangelock_enter(&zp->z_rangelock, 0, n, RL_APPEND);
                woff = lr->lr_offset;
                if (lr->lr_length == UINT64_MAX) {
                        /*
                         * We overlocked the file because this write will cause
                         * the file block size to increase.
                         * Note that zp_size cannot change with this lock held.
                         */
                        woff = zp->z_size;
                }
                zfs_uio_setoffset(uio, woff);
        } else {
                /*
                 * Note that if the file block size will change as a result of
                 * this write, then this range lock will lock the entire file
                 * so that we can re-write the block safely.
                 */
                lr = zfs_rangelock_enter(&zp->z_rangelock, woff, n, RL_WRITER);
        }

        if (zn_rlimit_fsize(zp, uio)) {
                zfs_rangelock_exit(lr);
                zfs_exit(zfsvfs, FTAG);
                return (SET_ERROR(EFBIG));
        }

        const rlim64_t limit = MAXOFFSET_T;

        if (woff >= limit) {
                zfs_rangelock_exit(lr);
                zfs_exit(zfsvfs, FTAG);
                return (SET_ERROR(EFBIG));
        }

        if (n > limit - woff)
                n = limit - woff;

        uint64_t end_size = MAX(zp->z_size, woff + n);
        zilog_t *zilog = zfsvfs->z_log;

        const uint64_t uid = KUID_TO_SUID(ZTOUID(zp));
        const uint64_t gid = KGID_TO_SGID(ZTOGID(zp));
        const uint64_t projid = zp->z_projid;

        /*
         * Write the file in reasonable size chunks.  Each chunk is written
         * in a separate transaction; this keeps the intent log records small
         * and allows us to do more fine-grained space accounting.
         */
        while (n > 0) {
                woff = zfs_uio_offset(uio);

                if (zfs_id_overblockquota(zfsvfs, DMU_USERUSED_OBJECT, uid) ||
                    zfs_id_overblockquota(zfsvfs, DMU_GROUPUSED_OBJECT, gid) ||
                    (projid != ZFS_DEFAULT_PROJID &&
                    zfs_id_overblockquota(zfsvfs, DMU_PROJECTUSED_OBJECT,
                    projid))) {
                        error = SET_ERROR(EDQUOT);
                        break;
                }

                arc_buf_t *abuf = NULL;
                if (n >= max_blksz && woff >= zp->z_size &&
                    P2PHASE(woff, max_blksz) == 0 &&
                    zp->z_blksz == max_blksz) {
                        /*
                         * This write covers a full block.  "Borrow" a buffer
                         * from the dmu so that we can fill it before we enter
                         * a transaction.  This avoids the possibility of
                         * holding up the transaction if the data copy hangs
                         * up on a pagefault (e.g., from an NFS server mapping).
                         */
                        size_t cbytes;

                        abuf = dmu_request_arcbuf(sa_get_db(zp->z_sa_hdl),
                            max_blksz);
                        ASSERT(abuf != NULL);
                        ASSERT(arc_buf_size(abuf) == max_blksz);
                        if ((error = zfs_uiocopy(abuf->b_data, max_blksz,
                            UIO_WRITE, uio, &cbytes))) {
                                dmu_return_arcbuf(abuf);
                                break;
                        }
                        ASSERT3S(cbytes, ==, max_blksz);
                }

                /*
                 * Start a transaction.
                 */
                dmu_tx_t *tx = dmu_tx_create(zfsvfs->z_os);
                dmu_tx_hold_sa(tx, zp->z_sa_hdl, B_FALSE);
                dmu_buf_impl_t *db = (dmu_buf_impl_t *)sa_get_db(zp->z_sa_hdl);
                DB_DNODE_ENTER(db);
                dmu_tx_hold_write_by_dnode(tx, DB_DNODE(db), woff,
                    MIN(n, max_blksz));
                DB_DNODE_EXIT(db);
                zfs_sa_upgrade_txholds(tx, zp);
                error = dmu_tx_assign(tx, TXG_WAIT);
                if (error) {
                        dmu_tx_abort(tx);
                        if (abuf != NULL)
                                dmu_return_arcbuf(abuf);
                        break;
                }

                /*
                 * NB: We must call zfs_clear_setid_bits_if_necessary before
                 * committing the transaction!
                 */

                /*
                 * If rangelock_enter() over-locked we grow the blocksize
                 * and then reduce the lock range.  This will only happen
                 * on the first iteration since rangelock_reduce() will
                 * shrink down lr_length to the appropriate size.
                 */
                if (lr->lr_length == UINT64_MAX) {
                        uint64_t new_blksz;

                        if (zp->z_blksz > max_blksz) {
                                /*
                                 * File's blocksize is already larger than the
                                 * "recordsize" property.  Only let it grow to
                                 * the next power of 2.
                                 */
                                ASSERT(!ISP2(zp->z_blksz));
                                new_blksz = MIN(end_size,
                                    1 << highbit64(zp->z_blksz));
                        } else {
                                new_blksz = MIN(end_size, max_blksz);
                        }
                        zfs_grow_blocksize(zp, new_blksz, tx);
                        zfs_rangelock_reduce(lr, woff, n);
                }

                /*
                 * XXX - should we really limit each write to z_max_blksz?
                 * Perhaps we should use SPA_MAXBLOCKSIZE chunks?
                 */
                const ssize_t nbytes =
                    MIN(n, max_blksz - P2PHASE(woff, max_blksz));

                ssize_t tx_bytes;
                if (abuf == NULL) {
                        tx_bytes = zfs_uio_resid(uio);
                        zfs_uio_fault_disable(uio, B_TRUE);
                        error = dmu_write_uio_dbuf(sa_get_db(zp->z_sa_hdl),
                            uio, nbytes, tx);
                        zfs_uio_fault_disable(uio, B_FALSE);
#ifdef __linux__
                        if (error == EFAULT) {
                                zfs_clear_setid_bits_if_necessary(zfsvfs, zp,
                                    cr, &clear_setid_bits_txg, tx);
                                dmu_tx_commit(tx);
                                /*
                                 * Account for partial writes before
                                 * continuing the loop.
                                 * Update needs to occur before the next
                                 * zfs_uio_prefaultpages, or prefaultpages may
                                 * error, and we may break the loop early.
                                 */
                                if (tx_bytes != zfs_uio_resid(uio))
                                        n -= tx_bytes - zfs_uio_resid(uio);
                                if (zfs_uio_prefaultpages(MIN(n, max_blksz),
                                    uio)) {
                                        break;
                                }
                                continue;
                        }
#endif
                        /*
                         * On FreeBSD, EFAULT should be propagated back to the
                         * VFS, which will handle faulting and will retry.
                         */
                        if (error != 0 && error != EFAULT) {
                                zfs_clear_setid_bits_if_necessary(zfsvfs, zp,
                                    cr, &clear_setid_bits_txg, tx);
                                dmu_tx_commit(tx);
                                break;
                        }
                        tx_bytes -= zfs_uio_resid(uio);
                } else {
                        /* Implied by abuf != NULL: */
                        ASSERT3S(n, >=, max_blksz);
                        ASSERT0(P2PHASE(woff, max_blksz));
                        /*
                         * We can simplify nbytes to MIN(n, max_blksz) since
                         * P2PHASE(woff, max_blksz) is 0, and knowing
                         * n >= max_blksz lets us simplify further:
                         */
                        ASSERT3S(nbytes, ==, max_blksz);
                        /*
                         * Thus, we're writing a full block at a block-aligned
                         * offset and extending the file past EOF.
                         *
                         * dmu_assign_arcbuf_by_dbuf() will directly assign the
                         * arc buffer to a dbuf.
                         */
                        error = dmu_assign_arcbuf_by_dbuf(
                            sa_get_db(zp->z_sa_hdl), woff, abuf, tx);
                        if (error != 0) {
                                /*
                                 * XXX This might not be necessary if
                                 * dmu_assign_arcbuf_by_dbuf is guaranteed
                                 * to be atomic.
                                 */
                                zfs_clear_setid_bits_if_necessary(zfsvfs, zp,
                                    cr, &clear_setid_bits_txg, tx);
                                dmu_return_arcbuf(abuf);
                                dmu_tx_commit(tx);
                                break;
                        }
                        ASSERT3S(nbytes, <=, zfs_uio_resid(uio));
                        zfs_uioskip(uio, nbytes);
                        tx_bytes = nbytes;
                }
                if (tx_bytes && zn_has_cached_data(zp) &&
                    !(ioflag & O_DIRECT)) {
                        update_pages(zp, woff, tx_bytes, zfsvfs->z_os);
                }

                /*
                 * If we made no progress, we're done.  If we made even
                 * partial progress, update the znode and ZIL accordingly.
                 */
                if (tx_bytes == 0) {
                        (void) sa_update(zp->z_sa_hdl, SA_ZPL_SIZE(zfsvfs),
                            (void *)&zp->z_size, sizeof (uint64_t), tx);
                        dmu_tx_commit(tx);
                        ASSERT(error != 0);
                        break;
                }

                zfs_clear_setid_bits_if_necessary(zfsvfs, zp, cr,
                    &clear_setid_bits_txg, tx);

                zfs_tstamp_update_setup(zp, CONTENT_MODIFIED, mtime, ctime);

                /*
                 * Update the file size (zp_size) if it has changed;
                 * account for possible concurrent updates.
                 */
                while ((end_size = zp->z_size) < zfs_uio_offset(uio)) {
                        (void) atomic_cas_64(&zp->z_size, end_size,
                            zfs_uio_offset(uio));
                        ASSERT(error == 0 || error == EFAULT);
                }
                /*
                 * If we are replaying and eof is non zero then force
                 * the file size to the specified eof. Note, there's no
                 * concurrency during replay.
                 */
                if (zfsvfs->z_replay && zfsvfs->z_replay_eof != 0)
                        zp->z_size = zfsvfs->z_replay_eof;

                error1 = sa_bulk_update(zp->z_sa_hdl, bulk, count, tx);
                if (error1 != 0)
                        /* Avoid clobbering EFAULT. */
                        error = error1;

                /*
                 * NB: During replay, the TX_SETATTR record logged by
                 * zfs_clear_setid_bits_if_necessary must precede any of
                 * the TX_WRITE records logged here.
                 */
                zfs_log_write(zilog, tx, TX_WRITE, zp, woff, tx_bytes, ioflag,
                    NULL, NULL);

                dmu_tx_commit(tx);

                if (error != 0)
                        break;
                ASSERT3S(tx_bytes, ==, nbytes);
                n -= nbytes;

                if (n > 0) {
                        if (zfs_uio_prefaultpages(MIN(n, max_blksz), uio)) {
                                error = SET_ERROR(EFAULT);
                                break;
                        }
                }
        }

        zfs_znode_update_vfs(zp);
        zfs_rangelock_exit(lr);

        /*
         * If we're in replay mode, or we made no progress, or the
         * uio data is inaccessible return an error.  Otherwise, it's
         * at least a partial write, so it's successful.
         */
        if (zfsvfs->z_replay || zfs_uio_resid(uio) == start_resid ||
            error == EFAULT) {
                zfs_exit(zfsvfs, FTAG);
                return (error);
        }

        if (ioflag & (O_SYNC | O_DSYNC) ||
            zfsvfs->z_os->os_sync == ZFS_SYNC_ALWAYS)
                zil_commit(zilog, zp->z_id);

        const int64_t nwritten = start_resid - zfs_uio_resid(uio);
        dataset_kstats_update_write_kstats(&zfsvfs->z_kstat, nwritten);
        task_io_account_write(nwritten);

        zfs_exit(zfsvfs, FTAG);
        return (0);
}

int
zfs_getsecattr(znode_t *zp, vsecattr_t *vsecp, int flag, cred_t *cr)
{
        zfsvfs_t *zfsvfs = ZTOZSB(zp);
        int error;
        boolean_t skipaclchk = (flag & ATTR_NOACLCHECK) ? B_TRUE : B_FALSE;

        if ((error = zfs_enter_verify_zp(zfsvfs, zp, FTAG)) != 0)
                return (error);
        error = zfs_getacl(zp, vsecp, skipaclchk, cr);
        zfs_exit(zfsvfs, FTAG);

        return (error);
}

int
zfs_setsecattr(znode_t *zp, vsecattr_t *vsecp, int flag, cred_t *cr)
{
        zfsvfs_t *zfsvfs = ZTOZSB(zp);
        int error;
        boolean_t skipaclchk = (flag & ATTR_NOACLCHECK) ? B_TRUE : B_FALSE;
        zilog_t *zilog = zfsvfs->z_log;

        if ((error = zfs_enter_verify_zp(zfsvfs, zp, FTAG)) != 0)
                return (error);

        error = zfs_setacl(zp, vsecp, skipaclchk, cr);

        if (zfsvfs->z_os->os_sync == ZFS_SYNC_ALWAYS)
                zil_commit(zilog, 0);

        zfs_exit(zfsvfs, FTAG);
        return (error);
}

#ifdef ZFS_DEBUG
static int zil_fault_io = 0;
#endif

static void zfs_get_done(zgd_t *zgd, int error);

/*
 * Get data to generate a TX_WRITE intent log record.
 */
int
zfs_get_data(void *arg, uint64_t gen, lr_write_t *lr, char *buf,
    struct lwb *lwb, zio_t *zio)
{
        zfsvfs_t *zfsvfs = arg;
        objset_t *os = zfsvfs->z_os;
        znode_t *zp;
        uint64_t object = lr->lr_foid;
        uint64_t offset = lr->lr_offset;
        uint64_t size = lr->lr_length;
        dmu_buf_t *db;
        zgd_t *zgd;
        int error = 0;
        uint64_t zp_gen;

        ASSERT3P(lwb, !=, NULL);
        ASSERT3P(zio, !=, NULL);
        ASSERT3U(size, !=, 0);

        /*
         * Nothing to do if the file has been removed
         */
        if (zfs_zget(zfsvfs, object, &zp) != 0)
                return (SET_ERROR(ENOENT));
        if (zp->z_unlinked) {
                /*
                 * Release the vnode asynchronously as we currently have the
                 * txg stopped from syncing.
                 */
                zfs_zrele_async(zp);
                return (SET_ERROR(ENOENT));
        }
        /* check if generation number matches */
        if (sa_lookup(zp->z_sa_hdl, SA_ZPL_GEN(zfsvfs), &zp_gen,
            sizeof (zp_gen)) != 0) {
                zfs_zrele_async(zp);
                return (SET_ERROR(EIO));
        }
        if (zp_gen != gen) {
                zfs_zrele_async(zp);
                return (SET_ERROR(ENOENT));
        }

        zgd = (zgd_t *)kmem_zalloc(sizeof (zgd_t), KM_SLEEP);
        zgd->zgd_lwb = lwb;
        zgd->zgd_private = zp;

        /*
         * Write records come in two flavors: immediate and indirect.
         * For small writes it's cheaper to store the data with the
         * log record (immediate); for large writes it's cheaper to
         * sync the data and get a pointer to it (indirect) so that
         * we don't have to write the data twice.
         */
        if (buf != NULL) { /* immediate write */
                zgd->zgd_lr = zfs_rangelock_enter(&zp->z_rangelock,
                    offset, size, RL_READER);
                /* test for truncation needs to be done while range locked */
                if (offset >= zp->z_size) {
                        error = SET_ERROR(ENOENT);
                } else {
                        error = dmu_read(os, object, offset, size, buf,
                            DMU_READ_NO_PREFETCH);
                }
                ASSERT(error == 0 || error == ENOENT);
        } else { /* indirect write */
                /*
                 * Have to lock the whole block to ensure when it's
                 * written out and its checksum is being calculated
                 * that no one can change the data. We need to re-check
                 * blocksize after we get the lock in case it's changed!
                 */
                for (;;) {
                        uint64_t blkoff;
                        size = zp->z_blksz;
                        blkoff = ISP2(size) ? P2PHASE(offset, size) : offset;
                        offset -= blkoff;
                        zgd->zgd_lr = zfs_rangelock_enter(&zp->z_rangelock,
                            offset, size, RL_READER);
                        if (zp->z_blksz == size)
                                break;
                        offset += blkoff;
                        zfs_rangelock_exit(zgd->zgd_lr);
                }
                /* test for truncation needs to be done while range locked */
                if (lr->lr_offset >= zp->z_size)
                        error = SET_ERROR(ENOENT);
#ifdef ZFS_DEBUG
                if (zil_fault_io) {
                        error = SET_ERROR(EIO);
                        zil_fault_io = 0;
                }
#endif
                if (error == 0)
                        error = dmu_buf_hold(os, object, offset, zgd, &db,
                            DMU_READ_NO_PREFETCH);

                if (error == 0) {
                        blkptr_t *bp = &lr->lr_blkptr;

                        zgd->zgd_db = db;
                        zgd->zgd_bp = bp;

                        ASSERT(db->db_offset == offset);
                        ASSERT(db->db_size == size);

                        error = dmu_sync(zio, lr->lr_common.lrc_txg,
                            zfs_get_done, zgd);
                        ASSERT(error || lr->lr_length <= size);

                        /*
                         * On success, we need to wait for the write I/O
                         * initiated by dmu_sync() to complete before we can
                         * release this dbuf.  We will finish everything up
                         * in the zfs_get_done() callback.
                         */
                        if (error == 0)
                                return (0);

                        if (error == EALREADY) {
                                lr->lr_common.lrc_txtype = TX_WRITE2;
                                /*
                                 * TX_WRITE2 relies on the data previously
                                 * written by the TX_WRITE that caused
                                 * EALREADY.  We zero out the BP because
                                 * it is the old, currently-on-disk BP.
                                 */
                                zgd->zgd_bp = NULL;
                                BP_ZERO(bp);
                                error = 0;
                        }
                }
        }

        zfs_get_done(zgd, error);

        return (error);
}


static void
zfs_get_done(zgd_t *zgd, int error)
{
        (void) error;
        znode_t *zp = zgd->zgd_private;

        if (zgd->zgd_db)
                dmu_buf_rele(zgd->zgd_db, zgd);

        zfs_rangelock_exit(zgd->zgd_lr);

        /*
         * Release the vnode asynchronously as we currently have the
         * txg stopped from syncing.
         */
        zfs_zrele_async(zp);

        kmem_free(zgd, sizeof (zgd_t));
}

EXPORT_SYMBOL(zfs_access);
EXPORT_SYMBOL(zfs_fsync);
EXPORT_SYMBOL(zfs_holey);
EXPORT_SYMBOL(zfs_read);
EXPORT_SYMBOL(zfs_write);
EXPORT_SYMBOL(zfs_getsecattr);
EXPORT_SYMBOL(zfs_setsecattr);

ZFS_MODULE_PARAM(zfs_vnops, zfs_vnops_, read_chunk_size, U64, ZMOD_RW,
        "Bytes to read per chunk");