[PATCH 42/74] libext2fs: only punch complete clusters

["Darrick J. Wong" <darrick.wong@oracle.com>]

When bigalloc is enabled, using ext2fs_block_alloc_stats2() to free
any block in a cluster has the effect of freeing the entire cluster.
This is problematic if a caller instructs us to punch, say, blocks
12-15 of a 16-block cluster, because blocks 0-11 now point to a "free"
cluster.

The naive way to solve this problem is to see if any of the other
blocks in this logical cluster map to a physical cluster.  If so, then
we know that the cluster is still in use and it mustn't be freed.
Otherwise, we are punching the last mapped block in this cluster, so
we can free the cluster.

The implementation given only does the rigorous checks for the partial
clusters at the beginning and end of the punching range.

v2: Refactor the block free code into a separate helper function that
should be more efficient.

Reviewed-by: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 lib/ext2fs/bmap.c   |   29 ++++++++++++++++++
 lib/ext2fs/ext2fs.h |    3 ++
 lib/ext2fs/punch.c  |   82 ++++++++++++++++++++++++++++++++++++++++++++++++---
 3 files changed, 109 insertions(+), 5 deletions(-)


diff --git a/lib/ext2fs/bmap.c b/lib/ext2fs/bmap.c
index 32788f6..3a18d76 100644
--- a/lib/ext2fs/bmap.c
+++ b/lib/ext2fs/bmap.c
@@ -173,6 +173,35 @@ static errcode_t implied_cluster_alloc(ext2_filsys fs, ext2_ino_t ino,
 	return 0;
 }
 
+/* Try to map a logical block to an already-allocated physical cluster. */
+errcode_t ext2fs_map_cluster_block(ext2_filsys fs, ext2_ino_t ino,
+				   struct ext2_inode *inode, blk64_t lblk,
+				   blk64_t *pblk)
+{
+	ext2_extent_handle_t handle;
+	errcode_t retval;
+
+	/* Need bigalloc and extents to be enabled */
+	*pblk = 0;
+	if (!EXT2_HAS_RO_COMPAT_FEATURE(fs->super,
+					EXT4_FEATURE_RO_COMPAT_BIGALLOC) ||
+	    !(inode->i_flags & EXT4_EXTENTS_FL))
+		return 0;
+
+	retval = ext2fs_extent_open2(fs, ino, inode, &handle);
+	if (retval)
+		goto out;
+
+	retval = implied_cluster_alloc(fs, ino, inode, handle, lblk, pblk);
+	if (retval)
+		goto out2;
+
+out2:
+	ext2fs_extent_free(handle);
+out:
+	return retval;
+}
+
 static errcode_t extent_bmap(ext2_filsys fs, ext2_ino_t ino,
 			     struct ext2_inode *inode,
 			     ext2_extent_handle_t handle,
diff --git a/lib/ext2fs/ext2fs.h b/lib/ext2fs/ext2fs.h
index edd5ee9..da518df 100644
--- a/lib/ext2fs/ext2fs.h
+++ b/lib/ext2fs/ext2fs.h
@@ -924,6 +924,9 @@ extern errcode_t ext2fs_bmap2(ext2_filsys fs, ext2_ino_t ino,
 			      struct ext2_inode *inode,
 			      char *block_buf, int bmap_flags, blk64_t block,
 			      int *ret_flags, blk64_t *phys_blk);
+errcode_t ext2fs_map_cluster_block(ext2_filsys fs, ext2_ino_t ino,
+				   struct ext2_inode *inode, blk64_t lblk,
+				   blk64_t *pblk);
 
 #if 0
 /* bmove.c */
diff --git a/lib/ext2fs/punch.c b/lib/ext2fs/punch.c
index ff051f7..f138297 100644
--- a/lib/ext2fs/punch.c
+++ b/lib/ext2fs/punch.c
@@ -177,6 +177,75 @@ static void dbg_print_extent(char *desc, struct ext2fs_extent *extent)
 #define dbg_printf(f, a...)		do { } while (0)
 #endif
 
+/* Free a range of blocks, respecting cluster boundaries */
+static errcode_t punch_extent_blocks(ext2_filsys fs, ext2_ino_t ino,
+				     struct ext2_inode *inode,
+				     blk64_t lfree_start, blk64_t free_start,
+				     __u32 free_count, int *freed)
+{
+	blk64_t		pblk;
+	int		freed_now = 0;
+	__u32		cluster_freed;
+	errcode_t	retval = 0;
+
+	/* No bigalloc?  Just free each block. */
+	if (EXT2FS_CLUSTER_RATIO(fs) == 1) {
+		*freed += free_count;
+		while (free_count-- > 0)
+			ext2fs_block_alloc_stats2(fs, free_start++, -1);
+		return retval;
+	}
+
+	/*
+	 * Try to free up to the next cluster boundary.  We assume that all
+	 * blocks in a logical cluster map to blocks from the same physical
+	 * cluster, and that the offsets within the [pl]clusters match.
+	 */
+	if (free_start & EXT2FS_CLUSTER_MASK(fs)) {
+		retval = ext2fs_map_cluster_block(fs, ino, inode,
+						  lfree_start, &pblk);
+		if (retval)
+			goto errout;
+		if (!pblk) {
+			ext2fs_block_alloc_stats2(fs, free_start, -1);
+			freed_now++;
+		}
+		cluster_freed = EXT2FS_CLUSTER_RATIO(fs) -
+			(free_start & EXT2FS_CLUSTER_MASK(fs));
+		if (cluster_freed > free_count)
+			cluster_freed = free_count;
+		free_count -= cluster_freed;
+		free_start += cluster_freed;
+		lfree_start += cluster_freed;
+	}
+
+	/* Free whole clusters from the middle of the range. */
+	while (free_count > 0 && free_count >= EXT2FS_CLUSTER_RATIO(fs)) {
+		ext2fs_block_alloc_stats2(fs, free_start, -1);
+		freed_now++;
+		cluster_freed = EXT2FS_CLUSTER_RATIO(fs);
+		free_count -= cluster_freed;
+		free_start += cluster_freed;
+		lfree_start += cluster_freed;
+	}
+
+	/* Try to free the last cluster. */
+	if (free_count > 0) {
+		retval = ext2fs_map_cluster_block(fs, ino, inode,
+						  lfree_start, &pblk);
+		if (retval)
+			goto errout;
+		if (!pblk) {
+			ext2fs_block_alloc_stats2(fs, free_start, -1);
+			freed_now++;
+		}
+	}
+
+errout:
+	*freed += freed_now;
+	return retval;
+}
+
 static errcode_t ext2fs_punch_extent(ext2_filsys fs, ext2_ino_t ino,
 				     struct ext2_inode *inode,
 				     blk64_t start, blk64_t end)
@@ -184,7 +253,7 @@ static errcode_t ext2fs_punch_extent(ext2_filsys fs, ext2_ino_t ino,
 	ext2_extent_handle_t	handle = 0;
 	struct ext2fs_extent	extent;
 	errcode_t		retval;
-	blk64_t			free_start, next;
+	blk64_t			free_start, next, lfree_start;
 	__u32			free_count, newlen;
 	int			freed = 0;
 	int			op;
@@ -225,6 +294,7 @@ static errcode_t ext2fs_punch_extent(ext2_filsys fs, ext2_ino_t ino,
 			/* Start of deleted region before extent; 
 			   adjust beginning of extent */
 			free_start = extent.e_pblk;
+			lfree_start = extent.e_lblk;
 			if (next > end)
 				free_count = end - extent.e_lblk + 1;
 			else
@@ -240,6 +310,7 @@ static errcode_t ext2fs_punch_extent(ext2_filsys fs, ext2_ino_t ino,
 			dbg_printf("Case #%d\n", 2);
 			newlen = start - extent.e_lblk;
 			free_start = extent.e_pblk + newlen;
+			lfree_start = extent.e_lblk + newlen;
 			free_count = extent.e_len - newlen;
 			extent.e_len = newlen;
 		} else {
@@ -255,6 +326,7 @@ static errcode_t ext2fs_punch_extent(ext2_filsys fs, ext2_ino_t ino,
 
 			extent.e_len = start - extent.e_lblk;
 			free_start = extent.e_pblk + extent.e_len;
+			lfree_start = extent.e_lblk + extent.e_len;
 			free_count = end - start + 1;
 
 			dbg_print_extent("inserting", &newex);
@@ -314,10 +386,10 @@ static errcode_t ext2fs_punch_extent(ext2_filsys fs, ext2_ino_t ino,
 			goto errout;
 		dbg_printf("Free start %llu, free count = %u\n",
 		       free_start, free_count);
-		while (free_count-- > 0) {
-			ext2fs_block_alloc_stats2(fs, free_start++, -1);
-			freed++;
-		}
+		retval = punch_extent_blocks(fs, ino, inode, lfree_start,
+					     free_start, free_count, &freed);
+		if (retval)
+			goto errout;
 	next_extent:
 		retval = ext2fs_extent_get(handle, op,
 					   &extent);