On Fri, Jun 04, 2021 at 09:09:04PM +0000, Satya Tangirala wrote: > Previously, bio_iov_iter_get_pages() wasn't used with bios that could have > an encryption context. However, direct I/O support using blk-crypto > introduces this possibility, so this function must now respect > bio_required_sector_alignment() (otherwise, xfstests like generic/465 with > ext4 will fail). Can you be more clear that the fscrypt direct I/O support only requires this in order to support I/O segments that aren't fs-block aligned? I do still wonder if we should just not support that... Dave is the only person who has asked for it, and it's a lot of trouble to support. I also noticed that f2fs has always only supported direct I/O that is *fully* fs-block aligned (including the I/O segments) anyway. So presumably that limitation is not really that important after all... Does anyone else have thoughts on this? One more comment on this patch below: > > Signed-off-by: Satya Tangirala <satyat@xxxxxxxxxx> > --- > block/bio.c | 13 ++++++++++++- > 1 file changed, 12 insertions(+), 1 deletion(-) > > diff --git a/block/bio.c b/block/bio.c > index 32f75f31bb5c..99c510f706e2 100644 > --- a/block/bio.c > +++ b/block/bio.c > @@ -1099,7 +1099,8 @@ static int __bio_iov_append_get_pages(struct bio *bio, struct iov_iter *iter) > * The function tries, but does not guarantee, to pin as many pages as > * fit into the bio, or are requested in @iter, whatever is smaller. If > * MM encounters an error pinning the requested pages, it stops. Error > - * is returned only if 0 pages could be pinned. > + * is returned only if 0 pages could be pinned. It also ensures that the number > + * of sectors added to the bio is aligned to bio_required_sector_alignment(). > * > * It's intended for direct IO, so doesn't do PSI tracking, the caller is > * responsible for setting BIO_WORKINGSET if necessary. > @@ -1107,6 +1108,7 @@ static int __bio_iov_append_get_pages(struct bio *bio, struct iov_iter *iter) > int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) > { > int ret = 0; > + unsigned int aligned_sectors; > > if (iov_iter_is_bvec(iter)) { > if (bio_op(bio) == REQ_OP_ZONE_APPEND) > @@ -1121,6 +1123,15 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) > ret = __bio_iov_iter_get_pages(bio, iter); > } while (!ret && iov_iter_count(iter) && !bio_full(bio, 0)); > > + /* > + * Ensure that number of sectors in bio is aligned to > + * bio_required_sector_align() > + */ > + aligned_sectors = round_down(bio_sectors(bio), > + bio_required_sector_alignment(bio)); > + iov_iter_revert(iter, (bio_sectors(bio) - aligned_sectors) << SECTOR_SHIFT); > + bio_truncate(bio, aligned_sectors << SECTOR_SHIFT); > + > /* don't account direct I/O as memory stall */ > bio_clear_flag(bio, BIO_WORKINGSET); > return bio->bi_vcnt ? 0 : ret; Doesn't this need to return an error if the bio's size gets rounded down to 0? For example if logical_block_size=512 and data_unit_size=4096, and the iov_iter points to 4096 bytes in 8 512-byte segments but the last one isn't mapped, then 7 pages would be pinned and the last one would fail. This would then truncate the bio's size to 0, but bio->bi_vcnt would be 7, so this would still return 0. It would also be necessary to release the pages before returning an error. - Eric
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