[2/3] btrfs: zstd: make the compression path to handle sector size < page size

Commit Message

Qu Wenruo Sept. 6, 2024, 5:16 a.m. UTC

Inside zstd_compress_folios(), after exhausted one input page, we need
to switch to the next page as input.

However when counting the total input bytes (@tot_in), we always increase
it by PAGE_SIZE.

For the following case, it can cause incorrect value:

        0          32K         64K          96K
        |          |///////////||///////////|

After compressing range [32K, 64K), we switch to the next page, and
increasing @tot_in by 64K, while we only read 32K.

This will cause the @total_in to return a value larger than the input
length.

Fix it by only increase @tot_in by the input size.

Signed-off-by: Qu Wenruo <[e-mail]>
---
 fs/btrfs/zstd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Patch

diff --git a/fs/btrfs/zstd.c b/fs/btrfs/zstd.c
index 866607fd3e58..15f8a83165a3 100644
--- a/fs/btrfs/zstd.c
+++ b/fs/btrfs/zstd.c
@@ -495,7 +495,7 @@  int zstd_compress_folios(struct list_head *ws, struct address_space *mapping,
 
 		/* Check if we need more input */
 		if (workspace->in_buf.pos == workspace->in_buf.size) {
-			tot_in += PAGE_SIZE;
+			tot_in += workspace->in_buf.size;
 			kunmap_local(workspace->in_buf.src);
 			workspace->in_buf.src = NULL;
 			folio_put(in_folio);