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Re: [PATCH v2] xfs: Make fiemap works with sparse file.

To: xfs@xxxxxxxxxxx
Subject: Re: [PATCH v2] xfs: Make fiemap works with sparse file.
From: Tao Ma <tao.ma@xxxxxxxxxx>
Date: Thu, 17 Jun 2010 16:53:19 +0800
Cc: linux-kernel@xxxxxxxxxxxxxxx, Tao Ma <tao.ma@xxxxxxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>, Alex Elder <aelder@xxxxxxx>, Christoph Hellwig <hch@xxxxxx>, Eric Sandeen <sandeen@xxxxxxxxxx>
In-reply-to: <20100614122912.GD6590@dastard>
References: <20100614122912.GD6590@dastard>
Hi Dave,
On 06/14/2010 08:29 PM, Dave Chinner wrote:
> I just had a thought - if you want to avoid holes being reported to
> fiemap, then add a BMV_IF_NO_HOLES flag to xfs_getbmap() and skip
> holes in the mappin gloop when this flag is set. That will make
> fiemap fill in the full number of extents without hacking the
> extent count...
Here is the updated one. I have used BVM_IF_NO_HOLES in xfs_getbmap
to skip increasing index 'cur_ext'. It is a bit ugly, see my commit
log. I guess maybe we can add another flag in xfs_bmapi so that it
don't even give us the holes?


>From cee1765ffd3e2b003b837666b4620b5107ed9ddd Mon Sep 17 00:00:00 2001
From: Tao Ma <tao.ma@xxxxxxxxxx>
Date: Thu, 17 Jun 2010 16:14:22 +0800
Subject: [PATCH v3] xfs: Make fiemap works with sparse file.

In xfs_vn_fiemap, we set bvm_count to fi_extent_max + 1 and want
to return fi_extent_max extents, but actually it won't work for
a sparse file. The reason is that in xfs_getbmap we will
calculate holes and set it in 'out', while out is malloced by
bmv_count(fi_extent_max+1) which didn't consider holes. So in the
worst case, if 'out' vector looks like
[hole, extent, hole, extent, hole, ... hole, extent, hole],
we will only return half of fi_extent_max extents.

This patch add a new parameter BMV_IF_NO_HOLES for bvm_iflags.
So with this flags, we don't use our 'out' in xfs_getbmap for
a hole. The solution is a bit ugly by just don't increasing
index of 'out' vector. I felt that it is not easy to skip it
at the very beginning since we have the complicated check and
some function like xfs_getbmapx_fix_eof_hole to adjust 'out'.

Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Alex Elder <aelder@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Eric Sandeen <sandeen@xxxxxxxxxx>
Signed-off-by: Tao Ma <tao.ma@xxxxxxxxxx>
 fs/xfs/linux-2.6/xfs_iops.c |    2 +-
 fs/xfs/xfs_bmap.c           |   14 +++++++++++++-
 fs/xfs/xfs_fs.h             |    4 +++-
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/linux-2.6/xfs_iops.c b/fs/xfs/linux-2.6/xfs_iops.c
index 9c8019c..505d5c0 100644
--- a/fs/xfs/linux-2.6/xfs_iops.c
+++ b/fs/xfs/linux-2.6/xfs_iops.c
@@ -677,7 +677,7 @@ xfs_vn_fiemap(
                                        fieinfo->fi_extents_max + 1;
        bm.bmv_count = min_t(__s32, bm.bmv_count,
                             (PAGE_SIZE * 16 / sizeof(struct getbmapx)));
-       bm.bmv_iflags = BMV_IF_PREALLOC;
+       bm.bmv_iflags = BMV_IF_PREALLOC | BMV_IF_NO_HOLES;
        if (fieinfo->fi_flags & FIEMAP_FLAG_XATTR)
                bm.bmv_iflags |= BMV_IF_ATTRFORK;
        if (!(fieinfo->fi_flags & FIEMAP_FLAG_SYNC))
diff --git a/fs/xfs/xfs_bmap.c b/fs/xfs/xfs_bmap.c
index 99587de..d49107d 100644
--- a/fs/xfs/xfs_bmap.c
+++ b/fs/xfs/xfs_bmap.c
@@ -5744,12 +5744,24 @@ xfs_getbmap(
                                goto out_free_map;
-                       nexleft--;
                        bmv->bmv_offset =
                                out[cur_ext].bmv_offset +
                        bmv->bmv_length =
                                max_t(__int64_t, 0, bmvend - bmv->bmv_offset);
+                       /*
+                        * In case we don't want to return the hole,
+                        * don't increase cur_ext so that we can reuse
+                        * it in the next loop.
+                        */
+                       if ((iflags & BMV_IF_NO_HOLES) &&
+                           out[cur_ext].bmv_block == -1LL) {
+                               memset(&out[cur_ext], 0, sizeof(out[cur_ext]));
+                               continue;
+                       }
+                       nexleft--;
diff --git a/fs/xfs/xfs_fs.h b/fs/xfs/xfs_fs.h
index 7cf7220..87c2e9d 100644
--- a/fs/xfs/xfs_fs.h
+++ b/fs/xfs/xfs_fs.h
@@ -114,8 +114,10 @@ struct getbmapx {
 #define BMV_IF_NO_DMAPI_READ   0x2     /* Do not generate DMAPI read event  */
 #define BMV_IF_PREALLOC                0x4     /* rtn status BMV_OF_PREALLOC 
if req */
 #define BMV_IF_DELALLOC                0x8     /* rtn status BMV_OF_DELALLOC 
if req */
+#define BMV_IF_NO_HOLES                0x10    /* Do not return holes */
 #define BMV_IF_VALID   \
 /*     bmv_oflags values - returned for each non-header segment */
 #define BMV_OF_PREALLOC                0x1     /* segment = unwritten 
pre-allocation */

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