Btrfs: move data checksumming into a dedicated tree

Btrfs stores checksums for each data block.  Until now, they have
been stored in the subvolume trees, indexed by the inode that is
referencing the data block.  This means that when we read the inode,
we've probably read in at least some checksums as well.

But, this has a few problems:

* The checksums are indexed by logical offset in the file.  When
compression is on, this means we have to do the expensive checksumming
on the uncompressed data.  It would be faster if we could checksum
the compressed data instead.

* If we implement encryption, we'll be checksumming the plain text and
storing that on disk.  This is significantly less secure.

* For either compression or encryption, we have to get the plain text
back before we can verify the checksum as correct.  This makes the raid
layer balancing and extent moving much more expensive.

* It makes the front end caching code more complex, as we have touch
the subvolume and inodes as we cache extents.

* There is potentitally one copy of the checksum in each subvolume
referencing an extent.

The solution used here is to store the extent checksums in a dedicated
tree.  This allows us to index the checksums by phyiscal extent
start and length.  It means:

* The checksum is against the data stored on disk, after any compression
or encryption is done.

* The checksum is stored in a central location, and can be verified without
following back references, or reading inodes.

This makes compression significantly faster by reducing the amount of
data that needs to be checksummed.  It will also allow much faster
raid management code in general.

The checksums are indexed by a key with a fixed objectid (a magic value
in ctree.h) and offset set to the starting byte of the extent.  This
allows us to copy the checksum items into the fsync log tree directly (or
any other tree), without having to invent a second format for them.

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

1 files changed, 109 insertions, 15 deletions

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 4febe2e..ad72741 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -69,11 +69,27 @@ struct compressed_bio {
 
 	/* IO errors */
 	int errors;
+	int mirror_num;
 
 	/* for reads, this is the bio we are copying the data into */
 	struct bio *orig_bio;
+
+	/*
+	 * the start of a variable length array of checksums only
+	 * used by reads
+	 */
+	u32 sums;
 };
 
+static inline int compressed_bio_size(struct btrfs_root *root,
+				      unsigned long disk_size)
+{
+	u16 csum_size = btrfs_super_csum_size(&root->fs_info->super_copy);
+	return sizeof(struct compressed_bio) +
+		((disk_size + root->sectorsize - 1) / root->sectorsize) *
+		csum_size;
+}
+
 static struct bio *compressed_bio_alloc(struct block_device *bdev,
 					u64 first_byte, gfp_t gfp_flags)
 {
@@ -96,6 +112,47 @@ static struct bio *compressed_bio_alloc(struct block_device *bdev,
 	return bio;
 }
 
+static int check_compressed_csum(struct inode *inode,
+				 struct compressed_bio *cb,
+				 u64 disk_start)
+{
+	int ret;
+	struct btrfs_root *root = BTRFS_I(inode)->root;
+	struct page *page;
+	unsigned long i;
+	char *kaddr;
+	u32 csum;
+	u32 *cb_sum = &cb->sums;
+
+	if (btrfs_test_opt(root, NODATASUM) ||
+	    btrfs_test_flag(inode, NODATASUM))
+		return 0;
+
+	for (i = 0; i < cb->nr_pages; i++) {
+		page = cb->compressed_pages[i];
+		csum = ~(u32)0;
+
+		kaddr = kmap_atomic(page, KM_USER0);
+		csum = btrfs_csum_data(root, kaddr, csum, PAGE_CACHE_SIZE);
+		btrfs_csum_final(csum, (char *)&csum);
+		kunmap_atomic(kaddr, KM_USER0);
+
+		if (csum != *cb_sum) {
+			printk("btrfs csum failed ino %lu extent %llu csum %u "
+			       "wanted %u mirror %d\n", inode->i_ino,
+			       (unsigned long long)disk_start,
+			       csum, *cb_sum, cb->mirror_num);
+			ret = -EIO;
+			goto fail;
+		}
+		cb_sum++;
+
+	}
+	ret = 0;
+fail:
+	return ret;
+}
+
 /* when we finish reading compressed pages from the disk, we
  * decompress them and then run the bio end_io routines on the
  * decompressed pages (in the inode address space).
@@ -124,16 +181,21 @@ static void end_compressed_bio_read(struct bio *bio, int err)
 	if (!atomic_dec_and_test(&cb->pending_bios))
 		goto out;
 
+	inode = cb->inode;
+	ret = check_compressed_csum(inode, cb, (u64)bio->bi_sector << 9);
+	if (ret)
+		goto csum_failed;
+
 	/* ok, we're the last bio for this extent, lets start
 	 * the decompression.
 	 */
-	inode = cb->inode;
 	tree = &BTRFS_I(inode)->io_tree;
 	ret = btrfs_zlib_decompress_biovec(cb->compressed_pages,
 					cb->start,
 					cb->orig_bio->bi_io_vec,
 					cb->orig_bio->bi_vcnt,
 					cb->compressed_len);
+csum_failed:
 	if (ret)
 		cb->errors = 1;
 
@@ -148,8 +210,21 @@ static void end_compressed_bio_read(struct bio *bio, int err)
 	/* do io completion on the original bio */
 	if (cb->errors) {
 		bio_io_error(cb->orig_bio);
-	} else
+	} else {
+		int bio_index = 0;
+		struct bio_vec *bvec = cb->orig_bio->bi_io_vec;
+
+		/*
+		 * we have verified the checksum already, set page
+		 * checked so the end_io handlers know about it
+		 */
+		while(bio_index < cb->orig_bio->bi_vcnt) {
+			SetPageChecked(bvec->bv_page);
+			bvec++;
+			bio_index++;
+		}
 		bio_endio(cb->orig_bio, 0);
+	}
 
 	/* finally free the cb struct */
 	kfree(cb->compressed_pages);
@@ -277,12 +352,13 @@ int btrfs_submit_compressed_write(struct inode *inode, u64 start,
 	int ret;
 
 	WARN_ON(start & ((u64)PAGE_CACHE_SIZE - 1));
-	cb = kmalloc(sizeof(*cb), GFP_NOFS);
+	cb = kmalloc(compressed_bio_size(root, compressed_len), GFP_NOFS);
 	atomic_set(&cb->pending_bios, 0);
 	cb->errors = 0;
 	cb->inode = inode;
 	cb->start = start;
 	cb->len = len;
+	cb->mirror_num = 0;
 	cb->compressed_pages = compressed_pages;
 	cb->compressed_len = compressed_len;
 	cb->orig_bio = NULL;
@@ -290,9 +366,6 @@ int btrfs_submit_compressed_write(struct inode *inode, u64 start,
 
 	bdev = BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;
 
-	ret = btrfs_csum_file_bytes(root, inode, start, len);
-	BUG_ON(ret);
-
 	bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS);
 	bio->bi_private = cb;
 	bio->bi_end_io = end_compressed_bio_write;
@@ -325,6 +398,9 @@ int btrfs_submit_compressed_write(struct inode *inode, u64 start,
 			ret = btrfs_bio_wq_end_io(root->fs_info, bio, 0);
 			BUG_ON(ret);
 
+			ret = btrfs_csum_one_bio(root, inode, bio, start, 1);
+			BUG_ON(ret);
+
 			ret = btrfs_map_bio(root, WRITE, bio, 0, 1);
 			BUG_ON(ret);
 
@@ -348,6 +424,9 @@ int btrfs_submit_compressed_write(struct inode *inode, u64 start,
 	ret = btrfs_bio_wq_end_io(root->fs_info, bio, 0);
 	BUG_ON(ret);
 
+	ret = btrfs_csum_one_bio(root, inode, bio, start, 1);
+	BUG_ON(ret);
+
 	ret = btrfs_map_bio(root, WRITE, bio, 0, 1);
 	BUG_ON(ret);
 
@@ -510,6 +589,7 @@ int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 	u64 em_start;
 	struct extent_map *em;
 	int ret;
+	u32 *sums;
 
 	tree = &BTRFS_I(inode)->io_tree;
 	em_tree = &BTRFS_I(inode)->extent_tree;
@@ -521,15 +601,18 @@ int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 				   PAGE_CACHE_SIZE);
 	spin_unlock(&em_tree->lock);
 
-	cb = kmalloc(sizeof(*cb), GFP_NOFS);
+	compressed_len = em->block_len;
+	cb = kmalloc(compressed_bio_size(root, compressed_len), GFP_NOFS);
 	atomic_set(&cb->pending_bios, 0);
 	cb->errors = 0;
 	cb->inode = inode;
+	cb->mirror_num = mirror_num;
+	sums = &cb->sums;
 
 	cb->start = em->orig_start;
-	compressed_len = em->block_len;
 	em_len = em->len;
 	em_start = em->start;
+
 	free_extent_map(em);
 	em = NULL;
 
@@ -551,11 +634,6 @@ int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 
 	add_ra_bio_pages(inode, em_start + em_len, cb);
 
-	if (!btrfs_test_opt(root, NODATASUM) &&
-	    !btrfs_test_flag(inode, NODATASUM)) {
-		btrfs_lookup_bio_sums(root, inode, cb->orig_bio);
-	}
-
 	/* include any pages we added in add_ra-bio_pages */
 	uncompressed_len = bio->bi_vcnt * PAGE_CACHE_SIZE;
 	cb->len = uncompressed_len;
@@ -568,6 +646,8 @@ int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 	for (page_index = 0; page_index < nr_pages; page_index++) {
 		page = cb->compressed_pages[page_index];
 		page->mapping = inode->i_mapping;
+		page->index = em_start >> PAGE_CACHE_SHIFT;
+
 		if (comp_bio->bi_size)
 			ret = tree->ops->merge_bio_hook(page, 0,
 							PAGE_CACHE_SIZE,
@@ -591,7 +671,16 @@ int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 			 */
 			atomic_inc(&cb->pending_bios);
 
-			ret = btrfs_map_bio(root, READ, comp_bio, 0, 0);
+			if (!btrfs_test_opt(root, NODATASUM) &&
+			    !btrfs_test_flag(inode, NODATASUM)) {
+				btrfs_lookup_bio_sums(root, inode, comp_bio,
+						      sums);
+			}
+			sums += (comp_bio->bi_size + root->sectorsize - 1) /
+				root->sectorsize;
+
+			ret = btrfs_map_bio(root, READ, comp_bio,
+					    mirror_num, 0);
 			BUG_ON(ret);
 
 			bio_put(comp_bio);
@@ -610,7 +699,12 @@ int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 	ret = btrfs_bio_wq_end_io(root->fs_info, comp_bio, 0);
 	BUG_ON(ret);
 
-	ret = btrfs_map_bio(root, READ, comp_bio, 0, 0);
+	if (!btrfs_test_opt(root, NODATASUM) &&
+	    !btrfs_test_flag(inode, NODATASUM)) {
+		btrfs_lookup_bio_sums(root, inode, comp_bio, sums);
+	}
+
+	ret = btrfs_map_bio(root, READ, comp_bio, mirror_num, 0);
 	BUG_ON(ret);
 
 	bio_put(comp_bio);