fsync.c

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/*
 *  linux/fs/ext4/fsync.c
 *
 *  Copyright (C) 1993  Stephen Tweedie ([email protected])
 *  from
 *  Copyright (C) 1992  Remy Card ([email protected])
 *                      Laboratoire MASI - Institut Blaise Pascal
 *                      Universite Pierre et Marie Curie (Paris VI)
 *  from
 *  linux/fs/minix/truncate.c   Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  ext4fs fsync primitive
 *
 *  Big-endian to little-endian byte-swapping/bitmaps by
 *        David S. Miller ([email protected]), 1995
 *
 *  Removed unnecessary code duplication for little endian machines
 *  and excessive __inline__s.
 *        Andi Kleen, 1997
 *
 * Major simplications and cleanup - we only need to do the metadata, because
 * we can depend on generic_block_fdatasync() to sync the data blocks.
 */

#include <linux/time.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/writeback.h>
#include <linux/jbd2.h>
#include <linux/blkdev.h>

#include "ext4.h"
#include "ext4_jbd2.h"

#include <trace/events/ext4.h>

/*
 * If we're not journaling and this is a just-created file, we have to
 * sync our parent directory (if it was freshly created) since
 * otherwise it will only be written by writeback, leaving a huge
 * window during which a crash may lose the file.  This may apply for
 * the parent directory's parent as well, and so on recursively, if
 * they are also freshly created.
 */
static int ext4_sync_parent(struct inode *inode)
{
    struct writeback_control wbc;
    struct dentry *dentry = NULL;
    struct inode *next;
    int ret = 0;

    if (!ext4_test_inode_state(inode, EXT4_STATE_NEWENTRY))
        return 0;
    inode = igrab(inode);
    while (ext4_test_inode_state(inode, EXT4_STATE_NEWENTRY)) {
        ext4_clear_inode_state(inode, EXT4_STATE_NEWENTRY);
        dentry = d_find_any_alias(inode);
        if (!dentry)
            break;
        next = igrab(dentry->d_parent->d_inode);
        dput(dentry);
        if (!next)
            break;
        iput(inode);
        inode = next;
        ret = sync_mapping_buffers(inode->i_mapping);
        if (ret)
            break;
        memset(&wbc, 0, sizeof(wbc));
        wbc.sync_mode = WB_SYNC_ALL;
        wbc.nr_to_write = 0;         /* only write out the inode */
        ret = sync_inode(inode, &wbc);
        if (ret)
            break;
    }
    iput(inode);
    return ret;
}

static int __sync_inode(struct inode *inode, int datasync)
{
    int err;
    int ret;

    ret = sync_mapping_buffers(inode->i_mapping);
    if (!(inode->i_state & I_DIRTY))
        return ret;
    if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))
        return ret;

    err = sync_inode_metadata(inode, 1);
    if (ret == 0)
        ret = err;
    return ret;
}

/*
 * akpm: A new design for ext4_sync_file().
 *
 * This is only called from sys_fsync(), sys_fdatasync() and sys_msync().
 * There cannot be a transaction open by this task.
 * Another task could have dirtied this inode.  Its data can be in any
 * state in the journalling system.
 *
 * What we do is just kick off a commit and wait on it.  This will snapshot the
 * inode to disk.
 *
 * i_mutex lock is held when entering and exiting this function
 */

int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
{
    struct inode *inode = file->f_mapping->host;
    struct ext4_inode_info *ei = EXT4_I(inode);
    journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
    int ret, err;
    tid_t commit_tid;
    bool needs_barrier = false;

    J_ASSERT(ext4_journal_current_handle() == NULL);

    trace_ext4_sync_file_enter(file, datasync);

    ret = filemap_write_and_wait_range(inode->i_mapping, start, end);
    if (ret)
        return ret;
    mutex_lock(&inode->i_mutex);

    if (inode->i_sb->s_flags & MS_RDONLY)
        goto out;

    ret = ext4_flush_unwritten_io(inode);
    if (ret < 0)
        goto out;

    if (!journal) {
        ret = __sync_inode(inode, datasync);
        if (!ret && !hlist_empty(&inode->i_dentry))
            ret = ext4_sync_parent(inode);
        goto out;
    }

    /*
     * data=writeback,ordered:
     *  The caller's filemap_fdatawrite()/wait will sync the data.
     *  Metadata is in the journal, we wait for proper transaction to
     *  commit here.
     *
     * data=journal:
     *  filemap_fdatawrite won't do anything (the buffers are clean).
     *  ext4_force_commit will write the file data into the journal and
     *  will wait on that.
     *  filemap_fdatawait() will encounter a ton of newly-dirtied pages
     *  (they were dirtied by commit).  But that's OK - the blocks are
     *  safe in-journal, which is all fsync() needs to ensure.
     */
    if (ext4_should_journal_data(inode)) {
        ret = ext4_force_commit(inode->i_sb);
        goto out;
    }

    commit_tid = datasync ? ei->i_datasync_tid : ei->i_sync_tid;
    if (journal->j_flags & JBD2_BARRIER &&
        !jbd2_trans_will_send_data_barrier(journal, commit_tid))
        needs_barrier = true;
    jbd2_log_start_commit(journal, commit_tid);
    ret = jbd2_log_wait_commit(journal, commit_tid);
    if (needs_barrier) {
        err = blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL);
        if (!ret)
            ret = err;
    }
 out:
    mutex_unlock(&inode->i_mutex);
    trace_ext4_sync_file_exit(inode, ret);
    return ret;
}