Btrfs: checksum file data at bio submission time instead of during writepage

When we checkum file data during writepage, the checksumming is done one
page at a time, making it difficult to do bulk metadata modifications
to insert checksums for large ranges of the file at once.

This patch changes btrfs to checksum on a per-bio basis instead.  The
bios are checksummed before they are handed off to the block layer, so
each bio is contiguous and only has pages from the same inode.

Checksumming on a bio basis allows us to insert and modify the file
checksum items in large groups.  It also allows the checksumming to
be done more easily by async worker threads.

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

1 files changed, 39 insertions, 11 deletions

diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
index 3ebbc058d08..3f0e71b0e5d 100644
--- a/fs/btrfs/file-item.c
+++ b/fs/btrfs/file-item.c
@@ -16,6 +16,9 @@
  * Boston, MA 021110-1307, USA.
  */
 
+#include <linux/bio.h>
+#include <linux/pagemap.h>
+#include <linux/highmem.h>
 #include "ctree.h"
 #include "disk-io.h"
 #include "transaction.h"
@@ -131,28 +134,35 @@ int btrfs_lookup_file_extent(struct btrfs_trans_handle *trans,
 	return ret;
 }
 
-int btrfs_csum_file_block(struct btrfs_trans_handle *trans,
-			  struct btrfs_root *root,
-			  struct inode *inode,
-			  u64 objectid, u64 offset,
-			  char *data, size_t len)
+int btrfs_csum_file_blocks(struct btrfs_trans_handle *trans,
+			   struct btrfs_root *root, struct inode *inode,
+			   struct bio *bio)
 {
+	u64 objectid = inode->i_ino;
+	u64 offset;
 	int ret;
 	struct btrfs_key file_key;
 	struct btrfs_key found_key;
-	u64 next_offset = (u64)-1;
-	int found_next = 0;
+	u64 next_offset;
+	int found_next;
 	struct btrfs_path *path;
 	struct btrfs_csum_item *item;
+	struct btrfs_csum_item *item_end;
 	struct extent_buffer *leaf = NULL;
 	u64 csum_offset;
-	u32 csum_result = ~(u32)0;
+	u32 csum_result;
 	u32 nritems;
 	u32 ins_size;
+	int bio_index = 0;
+	struct bio_vec *bvec = bio->bi_io_vec;
+	char *data;
 
 	path = btrfs_alloc_path();
 	BUG_ON(!path);
-
+again:
+	next_offset = (u64)-1;
+	found_next = 0;
+	offset = page_offset(bvec->bv_page) + bvec->bv_offset;
 	file_key.objectid = objectid;
 	file_key.offset = offset;
 	btrfs_set_key_type(&file_key, BTRFS_CSUM_ITEM_KEY);
@@ -259,7 +269,15 @@ csum:
 	item = (struct btrfs_csum_item *)((unsigned char *)item +
 					  csum_offset * BTRFS_CRC32_SIZE);
 found:
-	csum_result = btrfs_csum_data(root, data, csum_result, len);
+	item_end = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_csum_item);
+	item_end = (struct btrfs_csum_item *)((unsigned char *)item_end +
+				      btrfs_item_size_nr(leaf, path->slots[0]));
+next_bvec:
+	data = kmap_atomic(bvec->bv_page, KM_IRQ0);
+	csum_result = ~(u32)0;
+	csum_result = btrfs_csum_data(root, data + bvec->bv_offset,
+				      csum_result, bvec->bv_len);
+	kunmap_atomic(data, KM_IRQ0);
 	btrfs_csum_final(csum_result, (char *)&csum_result);
 	if (csum_result == 0) {
 		printk("csum result is 0 for inode %lu offset %Lu\n", inode->i_ino, offset);
@@ -267,9 +285,19 @@ found:
 
 	write_extent_buffer(leaf, &csum_result, (unsigned long)item,
 			    BTRFS_CRC32_SIZE);
+	bio_index++;
+	bvec++;
+	if (bio_index < bio->bi_vcnt) {
+		item = (struct btrfs_csum_item *)((char *)item + BTRFS_CRC32_SIZE);
+		if (item < item_end)
+			goto next_bvec;
+	}
 	btrfs_mark_buffer_dirty(path->nodes[0]);
+	if (bio_index < bio->bi_vcnt) {
+		btrfs_release_path(root, path);
+		goto again;
+	}
 fail:
-	btrfs_release_path(root, path);
 	btrfs_free_path(path);
 	return ret;
 }