Re: [PATCH 6/8] nowait aio: ext4
flat view
From: Jan Kara <jack@suse.cz>
Date: 2017-04-04 07:58:57
Also in:
linux-block, linux-btrfs, linux-ext4, linux-fsdevel, linux-xfs
On Mon 03-04-17 13:53:05, Goldwyn Rodrigues wrote:
From: Goldwyn Rodrigues <redacted> 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...
quoted hunk ↗ jump to hunk
@@ -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.
quoted hunk ↗ jump to hunk
--- 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 [off-list ref] SUSE Labs, CR