libext2fs: only punch complete clusters

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.

Reviewed-by: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/lib/ext2fs/bmap.c b/lib/ext2fs/bmap.c
index 32788f6f8e179a560f80c1f393d9c74da3f49ee5..3a18d76080af9d35bb7a7d28ec45c6dbb43b0455 100644 (file)
--- 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 c982327ec2a79e5cb6be4d7c619fe07f59aa05e8..fb6b0b439efd9abab3fee02bc2caedd776b1fda8 100644 (file)
--- a/lib/ext2fs/ext2fs.h
+++ b/lib/ext2fs/ext2fs.h
@@ -906,6 +906,9 @@ 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 37cb62c2a7a9b834a2eb87190b7ca31d08baeca8..9fff704862add0447b42a63e7bc9a135f302ccb5 100644 (file)
--- 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);