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iov_iter: don't require contiguous pages in iov_iter_extract_bvec_pages

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The iov_iter_extract_pages interface allows to return physically
discontiguous pages, as long as all but the first and last page
in the array are page aligned and page size.  Rewrite
iov_iter_extract_bvec_pages to take advantage of that instead of only
returning ranges of physically contiguous pages.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
[hch: minor cleanups, new commit log]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20241024050021.627350-1-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2024-10-24 07:00:15 +02:00 committed by Jens Axboe
parent f1be1788a3
commit e4e535bff2
1 changed files with 45 additions and 22 deletions
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67
lib/iov_iter.c
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@ -1677,8 +1677,8 @@ static ssize_t iov_iter_extract_xarray_pages(struct iov_iter *i,
}
/*
* Extract a list of contiguous pages from an ITER_BVEC iterator. This does
* not get references on the pages, nor does it get a pin on them.
* Extract a list of virtually contiguous pages from an ITER_BVEC iterator.
* This does not get references on the pages, nor does it get a pin on them.
*/
static ssize_t iov_iter_extract_bvec_pages(struct iov_iter *i,
struct page ***pages, size_t maxsize,
@ -1686,35 +1686,58 @@ static ssize_t iov_iter_extract_bvec_pages(struct iov_iter *i,
iov_iter_extraction_t extraction_flags,
size_t *offset0)
{
struct page **p, *page;
size_t skip = i->iov_offset, offset, size;
int k;
size_t skip = i->iov_offset, size = 0;
struct bvec_iter bi;
int k = 0;
for (;;) {
if (i->nr_segs == 0)
return 0;
size = min(maxsize, i->bvec->bv_len - skip);
if (size)
break;
if (i->nr_segs == 0)
return 0;
if (i->iov_offset == i->bvec->bv_len) {
i->iov_offset = 0;
i->nr_segs--;
i->bvec++;
skip = 0;
}
bi.bi_size = maxsize + skip;
bi.bi_bvec_done = skip;
skip += i->bvec->bv_offset;
page = i->bvec->bv_page + skip / PAGE_SIZE;
offset = skip % PAGE_SIZE;
*offset0 = offset;
maxpages = want_pages_array(pages, maxsize, skip, maxpages);
maxpages = want_pages_array(pages, size, offset, maxpages);
if (!maxpages)
return -ENOMEM;
p = *pages;
for (k = 0; k < maxpages; k++)
p[k] = page + k;
while (bi.bi_size && bi.bi_idx < i->nr_segs) {
struct bio_vec bv = bvec_iter_bvec(i->bvec, bi);
/*
* The iov_iter_extract_pages interface only allows an offset
* into the first page. Break out of the loop if we see an
* offset into subsequent pages, the caller will have to call
* iov_iter_extract_pages again for the reminder.
*/
if (k) {
if (bv.bv_offset)
break;
} else {
*offset0 = bv.bv_offset;
}
(*pages)[k++] = bv.bv_page;
size += bv.bv_len;
if (k >= maxpages)
break;
/*
* We are done when the end of the bvec doesn't align to a page
* boundary as that would create a hole in the returned space.
* The caller will handle this with another call to
* iov_iter_extract_pages.
*/
if (bv.bv_offset + bv.bv_len != PAGE_SIZE)
break;
bvec_iter_advance_single(i->bvec, &bi, bv.bv_len);
}
size = min_t(size_t, size, maxpages * PAGE_SIZE - offset);
iov_iter_advance(i, size);
return size;
}