On Mon 03-04-17 13:53:05, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
>
> Return EAGAIN if any of the following checks fail for direct I/O:
> + i_rwsem is lockable
> + Writing beyond end of file (will trigger allocation)
> + Blocks are not allocated at the write location
Patches seem to be missing your Signed-off-by tag...
> @@ -235,9 +237,21 @@ ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
>
> iocb->private = &overwrite;
> /* Check whether we do a DIO overwrite or not */
> - if (o_direct && ext4_should_dioread_nolock(inode) && !unaligned_aio &&
> - ext4_overwrite_io(inode, iocb->ki_pos, iov_iter_count(from)))
> - overwrite = 1;
> + if (o_direct && !unaligned_aio) {
> + struct ext4_map_blocks map;
> + if (ext4_blocks_mapped(inode, iocb->ki_pos,
> + iov_iter_count(from), &map)) {
> + /* To exclude unwritten extents, we need to check
> + * m_flags.
> + */
> + if (ext4_should_dioread_nolock(inode) &&
> + (map.m_flags & EXT4_MAP_MAPPED))
> + overwrite = 1;
> + } else if (iocb->ki_flags & IOCB_NOWAIT) {
> + ret = -EAGAIN;
> + goto out;
> + }
> + }
Actually, overwriting unwritten extents is relatively complex in ext4 as
well. In particular we need to start a transaction and split out the
written part of the extent. So I don't think we can easily support this
without blocking. As a result I'd keep the condition for IOCB_NOWAIT the
same as for overwrite IO.
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -117,7 +117,7 @@ static struct file_system_type ext2_fs_type = {
> .name = "ext2",
> .mount = ext4_mount,
> .kill_sb = kill_block_super,
> - .fs_flags = FS_REQUIRES_DEV,
> + .fs_flags = FS_REQUIRES_DEV | FS_NOWAIT,
FS_NOWAIT looks a bit too generic given these are filesystem feature flags.
Can we call it FS_NOWAIT_IO?
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
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