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io_uring/rsrc: refactor io_import_fixed

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io_import_fixed is a mess. Even though we know the final len of the
iterator, we still assign offset + len and do some magic after to
correct for that.

Do offset calculation first and finalise it with iov_iter_bvec at the
end.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/2d5107fed24f8b23245ef2ede9a5a7f7c426df61.1744882081.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2025-04-17 10:32:33 +01:00 committed by Jens Axboe
parent 50169d0754
commit 59852ebad9
1 changed files with 7 additions and 17 deletions
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24
io_uring/rsrc.c
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@ -1037,6 +1037,7 @@ static int io_import_fixed(int ddir, struct iov_iter *iter,
u64 buf_addr, size_t len)
{
const struct bio_vec *bvec;
unsigned nr_segs;
size_t offset;
int ret;
@ -1056,8 +1057,6 @@ static int io_import_fixed(int ddir, struct iov_iter *iter,
return 0;
}
iov_iter_bvec(iter, ddir, imu->bvec, imu->nr_bvecs, offset + len);
/*
* Don't use iov_iter_advance() here, as it's really slow for
* using the latter parts of a big fixed buffer - it iterates
@ -1067,30 +1066,21 @@ static int io_import_fixed(int ddir, struct iov_iter *iter,
* 1) it's a BVEC iter, we set it up
* 2) all bvecs are the same in size, except potentially the
* first and last bvec
*
* So just find our index, and adjust the iterator afterwards.
* If the offset is within the first bvec (or the whole first
* bvec, just use iov_iter_advance(). This makes it easier
* since we can just skip the first segment, which may not
* be folio_size aligned.
*/
bvec = imu->bvec;
if (offset < bvec->bv_len) {
iter->count -= offset;
iter->iov_offset = offset;
} else {
if (offset >= bvec->bv_len) {
unsigned long seg_skip;
/* skip first vec */
offset -= bvec->bv_len;
seg_skip = 1 + (offset >> imu->folio_shift);
iter->bvec += seg_skip;
iter->nr_segs -= seg_skip;
iter->count -= bvec->bv_len + offset;
iter->iov_offset = offset & ((1UL << imu->folio_shift) - 1);
bvec += seg_skip;
offset &= (1UL << imu->folio_shift) - 1;
}
nr_segs = imu->nr_bvecs - (bvec - imu->bvec);
iov_iter_bvec(iter, ddir, bvec, nr_segs, len);
iter->iov_offset = offset;
return 0;
}