On Fri, Nov 01, 2024 at 12:20:54PM +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. Hence, we should never 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]. > > While at it let's add an inline helper ext4_want_directio_fallback() which > simplifies the logic checks and inherently fixes condition on when to return > -ENOTBLK which otherwise was always returning true for any write or directio in > ext4_iomap_end(). It was ok since ext4 only supports direct-io via iomap. > > [1]: https://lore.kernel.org/linux-xfs/cover.1729825985.git.ritesh.list@xxxxxxxxx/T/#m9dbecc11bed713ed0d7a486432c56b105b555f04 > Suggested-by: Darrick J. Wong <djwong@xxxxxxxxxx> # inline helper Looks good to me now, Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx> --D > Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@xxxxxxxxx> > --- > fs/ext4/file.c | 7 +++++++ > fs/ext4/inode.c | 27 ++++++++++++++++++++++----- > 2 files changed, 29 insertions(+), 5 deletions(-) > > diff --git a/fs/ext4/file.c b/fs/ext4/file.c > index 96d936f5584b..a7de03e47db0 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 3e827cfa762e..5b9eeb74ce47 100644 > --- a/fs/ext4/inode.c > +++ b/fs/ext4/inode.c > @@ -3444,17 +3444,34 @@ static int ext4_iomap_overwrite_begin(struct inode *inode, loff_t offset, > return ret; > } > > +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; > +} > + > static int ext4_iomap_end(struct inode *inode, loff_t offset, loff_t length, > ssize_t written, unsigned flags, struct iomap *iomap) > { > /* > * 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 non-atomic writes, any blocks that may have been > + * allocated in preparation for the direct I/O will be reused during > + * buffered I/O. For atomic write, we never fallback to buffered-io. > */ > - if (flags & (IOMAP_WRITE | IOMAP_DIRECT) && written == 0) > + if (ext4_want_directio_fallback(flags, written)) > return -ENOTBLK; > > return 0; > -- > 2.46.0 > >
