[PATCH 5/5] brd: use memcpy_{to,from]_page in brd_rw_bvec

Christoph Hellwig
2025-04-21T07:27:15Z

Use the proper helpers to copy to/from potential highmem pages, which
do a local instead of atomic kmap underneath, and perform
flush_dcache_page where needed. This also simplifies the code so much
that the separate read write helpers are not required any more.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
drivers/block/brd.c | 57 ++++++++++-----------------------------------
1 file changed, 12 insertions(+), 45 deletions(-)

diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 580b2d8ce99c..79e96221f887 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -99,43 +99,6 @@ static void brd_free_pages(struct brd_device *brd)
xa_destroy(&brd->brd_pages);
}

-/*
- * Copy n bytes from src to the brd starting at sector. Does not sleep.
- */
-static void copy_to_brd(struct brd_device *brd, const void *src,
- sector_t sector, size_t n)
-{
- struct page *page;
- void *dst;
- unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
-
- page = brd_lookup_page(brd, sector);
- BUG_ON(!page);
-
- dst = kmap_atomic(page);
- memcpy(dst + offset, src, n);
- kunmap_atomic(dst);
-}
-
-/*
- * Copy n bytes to dst from the brd starting at sector. Does not sleep.
- */
-static void copy_from_brd(void *dst, struct brd_device *brd,
- sector_t sector, size_t n)
-{
- struct page *page;
- void *src;
- unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
-
- page = brd_lookup_page(brd, sector);
- if (page) {
- src = kmap_atomic(page);
- memcpy(dst, src + offset, n);
- kunmap_atomic(src);
- } else
- memset(dst, 0, n);
-}
-
/*
* Process a single segment. The segment is capped to not cross page boundaries
* in both the bio and the brd backing memory.
@@ -146,7 +109,8 @@ static bool brd_rw_bvec(struct brd_device *brd, struct bio *bio)
sector_t sector = bio->bi_iter.bi_sector;
u32 offset = (sector & (PAGE_SECTORS - 1)) << SECTOR_SHIFT;
blk_opf_t opf = bio->bi_opf;
- void *mem;
+ struct page *page;
+ void *kaddr;

bv.bv_len = min_t(u32, bv.bv_len, PAGE_SIZE - offset);

@@ -168,15 +132,18 @@ static bool brd_rw_bvec(struct brd_device *brd, struct bio *bio)
}
}

- mem = bvec_kmap_local(&bv);
- if (!op_is_write(opf)) {
- copy_from_brd(mem, brd, sector, bv.bv_len);
- flush_dcache_page(bv.bv_page);
+ page = brd_lookup_page(brd, sector);
+
+ kaddr = bvec_kmap_local(&bv);
+ if (op_is_write(opf)) {
+ BUG_ON(!page);
+ memcpy_to_page(page, offset, kaddr, bv.bv_len);
+ } else if (page) {
+ memcpy_from_page(kaddr, page, offset, bv.bv_len);
} else {
- flush_dcache_page(bv.bv_page);
- copy_to_brd(brd, mem, sector, bv.bv_len);
+ memset(kaddr, 0, bv.bv_len);
}
- kunmap_local(mem);
+ kunmap_local(kaddr);

bio_advance_iter_single(bio, &bio->bi_iter, bv.bv_len);
return true;
--
2.47.2