Btrfs: walk compressed pages based on the nr_pages count instead of bytes

The byte walk counting was awkward and error prone.  This uses the
number of pages sent the higher layer to build bios.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index c5470367ca5c..9adaa79adad9 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -296,7 +296,7 @@ int btrfs_submit_compressed_write(struct inode *inode, u64 start,
 
         /* create and submit bios for the compressed pages */
         bytes_left = compressed_len;
-        while(bytes_left > 0) {
+        for (page_index = 0; page_index < cb->nr_pages; page_index++) {
                 page = compressed_pages[page_index];
                 page->mapping = inode->i_mapping;
                 if (bio->bi_size)
@@ -324,7 +324,10 @@ int btrfs_submit_compressed_write(struct inode *inode, u64 start,
                         bio->bi_end_io = end_compressed_bio_write;
                         bio_add_page(bio, page, PAGE_CACHE_SIZE, 0);
                 }
-                page_index++;
+                if (bytes_left < PAGE_CACHE_SIZE) {
+                        printk("bytes left %lu compress len %lu nr %lu\n",
+                               bytes_left, cb->compressed_len, cb->nr_pages);
+                }
                 bytes_left -= PAGE_CACHE_SIZE;
                 first_byte += PAGE_CACHE_SIZE;
         }