btrfs: zstd: make the compression path to handle sector size < page size

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 <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/zstd.c b/fs/btrfs/zstd.c
index 866607fd3e588450f9e8cb4e55303a6d130bd567..15f8a83165a38b83024dd4e6bd1061f3953d6e6f 100644 (file)
--- 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);