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    Subject[PATCH 01/14] iomap: iomap that extends beyond EOF should be marked dirty
    Date
    From: Dave Chinner <dchinner@redhat.com>

    When doing a direct IO that spans the current EOF, and there are
    written blocks beyond EOF that extend beyond the current write, the
    only metadata update that needs to be done is a file size extension.

    However, we don't mark such iomaps as IOMAP_F_DIRTY to indicate that
    there is IO completion metadata updates required, and hence we may
    fail to correctly sync file size extensions made in IO completion
    when O_DSYNC writes are being used and the hardware supports FUA.

    Hence when setting IOMAP_F_DIRTY, we need to also take into account
    whether the iomap spans the current EOF. If it does, then we need to
    mark it dirty so that IO completion will call generic_write_sync()
    to flush the inode size update to stable storage correctly.

    Signed-off-by: Dave Chinner <dchinner@redhat.com>
    Signed-off-by: Christoph Hellwig <hch@lst.de>
    ---
    fs/ext4/inode.c | 9 ++++++++-
    fs/xfs/xfs_iomap.c | 7 +++++++
    include/linux/iomap.h | 2 ++
    3 files changed, 17 insertions(+), 1 deletion(-)

    diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
    index 516faa280ced..e9dc52537e5b 100644
    --- a/fs/ext4/inode.c
    +++ b/fs/ext4/inode.c
    @@ -3523,9 +3523,16 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
    return ret;
    }

    + /*
    + * Writes that span EOF might trigger an IO size update on completion,
    + * so consider them to be dirty for the purposes of O_DSYNC even if
    + * there is no other metadata changes being made or are pending here.
    + */
    iomap->flags = 0;
    - if (ext4_inode_datasync_dirty(inode))
    + if (ext4_inode_datasync_dirty(inode) ||
    + offset + length > i_size_read(inode))
    iomap->flags |= IOMAP_F_DIRTY;
    +
    iomap->bdev = inode->i_sb->s_bdev;
    iomap->dax_dev = sbi->s_daxdev;
    iomap->offset = (u64)first_block << blkbits;
    diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
    index f780e223b118..32993c2acbd9 100644
    --- a/fs/xfs/xfs_iomap.c
    +++ b/fs/xfs/xfs_iomap.c
    @@ -1049,6 +1049,13 @@ xfs_file_iomap_begin(
    trace_xfs_iomap_alloc(ip, offset, length, XFS_DATA_FORK, &imap);

    out_finish:
    + /*
    + * Writes that span EOF might trigger an IO size update on completion,
    + * so consider them to be dirty for the purposes of O_DSYNC even if
    + * there is no other metadata changes pending or have been made here.
    + */
    + if ((flags & IOMAP_WRITE) && offset + length > i_size_read(inode))
    + iomap->flags |= IOMAP_F_DIRTY;
    return xfs_bmbt_to_iomap(ip, iomap, &imap, shared);

    out_found:
    diff --git a/include/linux/iomap.h b/include/linux/iomap.h
    index 7aa5d6117936..24bd227d59f9 100644
    --- a/include/linux/iomap.h
    +++ b/include/linux/iomap.h
    @@ -32,6 +32,8 @@ struct vm_fault;
    *
    * IOMAP_F_DIRTY indicates the inode has uncommitted metadata needed to access
    * written data and requires fdatasync to commit them to persistent storage.
    + * This needs to take into account metadata changes that *may* be made at IO
    + * completion, such as file size updates from direct IO.
    */
    #define IOMAP_F_NEW 0x01 /* blocks have been newly allocated */
    #define IOMAP_F_DIRTY 0x02 /* uncommitted metadata */
    --
    2.20.1
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