Btrfs: export btrfs space shared info to userspace
authorLiu Bo <bo.li.liu@oracle.com>
Sun, 22 Sep 2013 04:54:23 +0000 (12:54 +0800)
committerChris Mason <chris.mason@fusionio.com>
Tue, 12 Nov 2013 02:52:54 +0000 (21:52 -0500)
Similar to ocfs2, btrfs also supports that extents can be shared by
different inodes, and there are some userspace tools requesting
for this kind of 'space shared infomation'.[1]

ocfs2 uses flag FIEMAP_EXTENT_SHARED, so does btrfs.

[1]: http://thr3ads.net/ocfs2-devel/2010/09/489052-PATCH-3-3-shared-du-using-fiemap-to-figure-up-the-shared-extents-per-file-and-the-footprint-in

Reviewed-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>
fs/btrfs/extent_io.c

index 51731b76900de55e8350d5795feacc61a9050d02..2bf6f46fae447416cd1546b8a25e5599f8ce81f3 100644 (file)
@@ -20,6 +20,7 @@
 #include "check-integrity.h"
 #include "locking.h"
 #include "rcu-string.h"
+#include "backref.h"
 
 static struct kmem_cache *extent_state_cache;
 static struct kmem_cache *extent_buffer_cache;
@@ -4062,6 +4063,19 @@ static struct extent_map *get_extent_skip_holes(struct inode *inode,
        return NULL;
 }
 
+static noinline int count_ext_ref(u64 inum, u64 offset, u64 root_id, void *ctx)
+{
+       unsigned long cnt = *((unsigned long *)ctx);
+
+       cnt++;
+       *((unsigned long *)ctx) = cnt;
+
+       /* Now we're sure that the extent is shared. */
+       if (cnt > 1)
+               return 1;
+       return 0;
+}
+
 int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
                __u64 start, __u64 len, get_extent_t *get_extent)
 {
@@ -4128,7 +4142,7 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
                last = found_key.offset;
                last_for_get_extent = last + 1;
        }
-       btrfs_free_path(path);
+       btrfs_release_path(path);
 
        /*
         * we might have some extents allocated but more delalloc past those
@@ -4198,7 +4212,24 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
                        flags |= (FIEMAP_EXTENT_DELALLOC |
                                  FIEMAP_EXTENT_UNKNOWN);
                } else {
+                       unsigned long ref_cnt = 0;
+
                        disko = em->block_start + offset_in_extent;
+
+                       /*
+                        * As btrfs supports shared space, this information
+                        * can be exported to userspace tools via
+                        * flag FIEMAP_EXTENT_SHARED.
+                        */
+                       ret = iterate_inodes_from_logical(
+                                       em->block_start,
+                                       BTRFS_I(inode)->root->fs_info,
+                                       path, count_ext_ref, &ref_cnt);
+                       if (ret < 0 && ret != -ENOENT)
+                               goto out_free;
+
+                       if (ref_cnt > 1)
+                               flags |= FIEMAP_EXTENT_SHARED;
                }
                if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags))
                        flags |= FIEMAP_EXTENT_ENCODED;
@@ -4230,6 +4261,7 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 out_free:
        free_extent_map(em);
 out:
+       btrfs_free_path(path);
        unlock_extent_cached(&BTRFS_I(inode)->io_tree, start, start + len - 1,
                             &cached_state, GFP_NOFS);
        return ret;