On Mon, Apr 29, 2024 at 05:47:39PM +0000, John Garry wrote:
> For FS_XFLAG_FORCEALIGN support, we want to treat any sub-extent IO like
> sub-fsblock DIO, in that we will zero the sub-extent when the mapping is
> unwritten.
>
> This will be important for atomic writes support, in that atomically
> writing over a partially written extent would mean that we would need to
> do the unwritten extent conversion write separately, and the write could
> no longer be atomic.
>
> It is the task of the FS to set iomap.extent_size per iter to indicate
> sub-extent zeroing required.
>
> Signed-off-by: John Garry <john.g.garry@xxxxxxxxxx>
Shouldn't this be done before the XFS feature is enabled in the
series?
> ---
> fs/iomap/direct-io.c | 17 +++++++++++------
> include/linux/iomap.h | 1 +
> 2 files changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index f3b43d223a46..a3ed7cfa95bc 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -277,7 +277,7 @@ static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter,
> {
> const struct iomap *iomap = &iter->iomap;
> struct inode *inode = iter->inode;
> - unsigned int fs_block_size = i_blocksize(inode), pad;
> + unsigned int zeroing_size, pad;
> loff_t length = iomap_length(iter);
> loff_t pos = iter->pos;
> blk_opf_t bio_opf;
> @@ -288,6 +288,11 @@ static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter,
> size_t copied = 0;
> size_t orig_count;
>
> + if (iomap->extent_size)
> + zeroing_size = iomap->extent_size;
> + else
> + zeroing_size = i_blocksize(inode);
Oh, the dissonance!
iomap->extent_size isn't an extent size at all.
The size of the extent the iomap returns is iomap->length. This new
variable is the IO specific "block size" that should be assumed by
the dio code to determine if padding should be done.
IOWs, I think we should add an "io_block_size" field to the iomap,
and every filesystem that supports iomap should set it to the
filesystem block size (i_blocksize(inode)). Then the changes to the
iomap code end up just being:
- unsigned int fs_block_size = i_blocksize(inode), pad;
+ unsigned int fs_block_size = iomap->io_block_size, pad;
And the patch that introduces that infrastructure change will also
change all the filesystem implementations to unconditionally set
iomap->io_block_size to i_blocksize().
Then, in a separate patch, you can add XFS support for large IO
block sizes when we have either a large rtextsize or extent size
hints set.
> +
> if ((pos | length) & (bdev_logical_block_size(iomap->bdev) - 1) ||
> !bdev_iter_is_aligned(iomap->bdev, dio->submit.iter))
> return -EINVAL;
> @@ -354,8 +359,8 @@ static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter,
> dio->iocb->ki_flags &= ~IOCB_HIPRI;
>
> if (need_zeroout) {
> - /* zero out from the start of the block to the write offset */
> - pad = pos & (fs_block_size - 1);
> + /* zero out from the start of the region to the write offset */
> + pad = pos & (zeroing_size - 1);
> if (pad)
> iomap_dio_zero(iter, dio, pos - pad, pad);
> }
> @@ -428,10 +433,10 @@ static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter,
> zero_tail:
> if (need_zeroout ||
> ((dio->flags & IOMAP_DIO_WRITE) && pos >= i_size_read(inode))) {
> - /* zero out from the end of the write to the end of the block */
> - pad = pos & (fs_block_size - 1);
> + /* zero out from the end of the write to the end of the region */
> + pad = pos & (zeroing_size - 1);
> if (pad)
> - iomap_dio_zero(iter, dio, pos, fs_block_size - pad);
> + iomap_dio_zero(iter, dio, pos, zeroing_size - pad);
> }
> out:
> /* Undo iter limitation to current extent */
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 6fc1c858013d..42623b1cdc04 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -97,6 +97,7 @@ struct iomap {
> u64 length; /* length of mapping, bytes */
> u16 type; /* type of mapping */
> u16 flags; /* flags for mapping */
> + unsigned int extent_size;
This needs a descriptive comment. At minimum, it should tell the
reader what units are used for the variable. If it is bytes, then
it needs to be a u64, because XFS can have extent size hints well
beyond 2^32 bytes in length.
-Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
