"Darrick J. Wong" <djwong@xxxxxxxxxx> writes: > On Wed, Oct 30, 2024 at 09:27:41PM +0530, Ritesh Harjani (IBM) wrote: >> atomic writes is currently only supported for single fsblock and only >> for direct-io. We should not return -ENOTBLK for atomic writes since we >> want the atomic write request to either complete fully or fail >> otherwise. We should not fallback to buffered-io in case of DIO atomic >> write requests. >> Let's also catch if this ever happens by adding some WARN_ON_ONCE before >> buffered-io handling for direct-io atomic writes. >> >> More details of the discussion [1]. >> >> [1]: https://lore.kernel.org/linux-xfs/cover.1729825985.git.ritesh.list@xxxxxxxxx/T/#m9dbecc11bed713ed0d7a486432c56b105b555f04 >> >> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@xxxxxxxxx> >> --- >> fs/ext4/file.c | 7 +++++++ >> fs/ext4/inode.c | 14 +++++++++----- >> 2 files changed, 16 insertions(+), 5 deletions(-) >> >> diff --git a/fs/ext4/file.c b/fs/ext4/file.c >> index 8116bd78910b..61787a37e9d4 100644 >> --- a/fs/ext4/file.c >> +++ b/fs/ext4/file.c >> @@ -599,6 +599,13 @@ static ssize_t ext4_dio_write_iter(struct kiocb *iocb, struct iov_iter *from) >> ssize_t err; >> loff_t endbyte; >> >> + /* >> + * There is no support for atomic writes on buffered-io yet, >> + * we should never fallback to buffered-io for DIO atomic >> + * writes. >> + */ >> + WARN_ON_ONCE(iocb->ki_flags & IOCB_ATOMIC); >> + >> offset = iocb->ki_pos; >> err = ext4_buffered_write_iter(iocb, from); >> if (err < 0) >> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c >> index fcdee27b9aa2..26b3c84d7f64 100644 >> --- a/fs/ext4/inode.c >> +++ b/fs/ext4/inode.c >> @@ -3449,12 +3449,16 @@ static int ext4_iomap_end(struct inode *inode, loff_t offset, loff_t length, >> { >> /* >> * Check to see whether an error occurred while writing out the data to >> - * the allocated blocks. If so, return the magic error code so that we >> - * fallback to buffered I/O and attempt to complete the remainder of >> - * the I/O. Any blocks that may have been allocated in preparation for >> - * the direct I/O will be reused during buffered I/O. >> + * the allocated blocks. If so, return the magic error code for >> + * non-atomic write so that we fallback to buffered I/O and attempt to >> + * complete the remainder of the I/O. >> + * For atomic writes we will simply fail the I/O request if we coudn't >> + * write anything. For non-atomic writes, any blocks that may have been >> + * allocated in preparation for the direct I/O will be reused during >> + * buffered I/O. >> */ >> - if (flags & (IOMAP_WRITE | IOMAP_DIRECT) && written == 0) >> + if (!(flags & IOMAP_ATOMIC) && (flags & (IOMAP_WRITE | IOMAP_DIRECT)) > > Huh. The WRITE|DIRECT check doesn't look right to me, because the > expression returns true for any write or any directio. I think that's > currently "ok" because ext4_iomap_end is only called for directio > writes, but this bugs me anyway. For a directio write fallback, that > comparison really should be: > > (flags & (WRITE|DIRECT)) == (WRITE|DIRECT) > yes. You are right. It is working since ext4 only supports iomap for DIRECTIO. But I agree it's better be fixed to avoid problem in future. > static inline bool > ext4_want_directio_fallback(unsigned flags, ssize_t written) > { > /* must be a directio to fall back to buffered */ > if (flags & (IOMAP_WRITE | IOMAP_DIRECT)) != > (IOMAP_WRITE | IOMAP_DIRECT) > return false; > > /* atomic writes are all-or-nothing */ > if (flags & IOMAP_ATOMIC) > return false; > > /* can only try again if we wrote nothing */ > return written == 0; > } > > if (ext4_want_directio_fallback(flags, written)) > return -ENOTBLK; > I like the above helper. Thanks for doing that. I will incorporate this in v4. >> + && written == 0) > > Nit: put the '&&' operator on the previous line when there's a multiline > expression. > I guess we don't need this if we do it with your above inline helper. But sure, next time will keep in mind for any such changes. > --D > Thanks for the review! -ritesh >> return -ENOTBLK; >> >> return 0; >> -- >> 2.46.0 >> >>
