[RFC PATCH] Btrfs: export btrfs space shared info to userspace

[RFC PATCH] Btrfs: export btrfs space shared info to userspace

[Liu Bo]

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

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
---
 fs/btrfs/extent_io.c |   34 +++++++++++++++++++++++++++++++++-
 1 files changed, 33 insertions(+), 1 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index fe443fe..2b3dd4a 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -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;
@@ -3957,6 +3958,19 @@ 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)
+{
+	int cnt = *((int *)ctx);
+
+	cnt++;
+	*((int *)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)
 {
@@ -4023,7 +4037,7 @@ 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
@@ -4093,7 +4107,24 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 			flags |= (FIEMAP_EXTENT_DELALLOC |
 				  FIEMAP_EXTENT_UNKNOWN);
 		} else {
+			int 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)
+				goto out_free;
+
+			if (ref_cnt > 1)
+				flags |= FIEMAP_EXTENT_SHARED;
 		}
 		if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags))
 			flags |= FIEMAP_EXTENT_ENCODED;
@@ -4127,6 +4158,7 @@ out_free:
 out:
 	unlock_extent_cached(&BTRFS_I(inode)->io_tree, start, start + len - 1,
 			     &cached_state, GFP_NOFS);
+	btrfs_free_path(path);
 	return ret;
 }
 
-- 
1.7.7

Re: [RFC PATCH] Btrfs: export btrfs space shared info to userspace

[David Sterba]

On Fri, Aug 16, 2013 at 04:27:28PM +0800, Liu Bo wrote:
> 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.

Looks ok to me.

> +			int ref_cnt = 0;

I think using long is cleaner here, it always fits into (void*), int
does not.

> +			/*
> +			 * 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)
> +				goto out_free;
> +
> +			if (ref_cnt > 1)
> +				flags |= FIEMAP_EXTENT_SHARED;

AFAICS, e2fsprogs filefrag does not yet know about FIEMAP_EXTENT_SHARED.

david

Re: [RFC PATCH] Btrfs: export btrfs space shared info to userspace

[Liu Bo]

On Wed, Aug 28, 2013 at 07:29:38PM +0200, David Sterba wrote:
> On Fri, Aug 16, 2013 at 04:27:28PM +0800, Liu Bo wrote:
> > 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.
> 
> Looks ok to me.
> 
> > +			int ref_cnt = 0;
> 
> I think using long is cleaner here, it always fits into (void*), int
> does not.

Good point.

> 
> > +			/*
> > +			 * 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)
> > +				goto out_free;
> > +
> > +			if (ref_cnt > 1)
> > +				flags |= FIEMAP_EXTENT_SHARED;
> 
> AFAICS, e2fsprogs filefrag does not yet know about FIEMAP_EXTENT_SHARED.

With checking filefrag's code, it's easy to make filefrag aware of this
flag.

I'll make a patch for filefrag unless someone has already done it, thanks.

-liubo