On 24.08.2017 19:03, Eric Sandeen wrote:

On 8/24/17 6:47 AM, Nikolay Borisov wrote:

quoted

Currently the semantics of the -n argument are a bit idiosyncratic. We want the
argument to be the limit of extents that are going to be output by the tool. This
is clearly broken now as evident from the following example on a fragmented file:

xfs_io -c "fiemap -v -n 5" test-dir/fragmented-file
test-dir/fragmented-file:
 EXT: FILE-OFFSET      BLOCK-RANGE          TOTAL FLAGS
   0: [0..15]:         hole                    16
   1: [16..23]:        897847296..897847303     8   0x0
   2: [24..31]:        hole                     8
   3: [32..39]:        897851392..897851399     8   0x0

So we want at most 5 extents printed, yet we get 4. So we always print n - 1
extents.

With this modification the output looks like:

xfs_io -c "fiemap -v -n 5" test-dir/fragmented-file
test-dir/fragmented-file:
 EXT: FILE-OFFSET      BLOCK-RANGE          TOTAL FLAGS
   0: [0..15]:         hole                    16
   1: [16..23]:        897847296..897847303     8   0x0
   2: [24..31]:        hole                     8
   3: [32..39]:        897851392..897851399     8   0x0
   4: [40..47]:        hole                     8

Signed-off-by: Nikolay Borisov <redacted>
---
 io/fiemap.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/io/fiemap.c b/io/fiemap.c
index 44a64870d711..7b275275465d 100644
--- a/io/fiemap.c
+++ b/io/fiemap.c

@@ -122,7 +122,7 @@ print_verbose(
 		cur_extent++;
 	}
 
-	if ((cur_extent + 1) == max_extents)
+	if (cur_extent == max_extents)
 		return 1;
 
 	snprintf(lbuf, sizeof(lbuf), "[%llu..%llu]:", lstart,

@@ -157,7 +157,7 @@ print_plain(
 		cur_extent++;
 	}
 
-	if ((cur_extent + 1) == max_extents)
+	if (cur_extent == max_extents)
 		return 1;
 
 	printf("\t%d: [%llu..%llu]: %llu..%llu", cur_extent,

@@ -264,7 +264,7 @@ fiemap_f(
 
 	printf("%s:\n", file->name);
 
-	while (!last && ((cur_extent + 1) != max_extents)) {
+	while (!last && (cur_extent != max_extents)) {

In my testing, for a bare fiemap (no -n) we get here with
cur_extent == max_extents == 0 and so nothing happens:

# xfs_io -c fiemap testfile
testfile:
#

(this causes every xfstest which invokes fiemap to fail).

I think initializing max_extents to -1 is a simple way to fix this.

Ah, you are right, I've come to the same conclusion during my testing of
earlier versions. Would you care to fold that fix if that's the only
problem found?

quoted

 
 		memset(fiemap, 0, map_size);
 		fiemap->fm_flags = fiemap_flags;

@@ -314,12 +314,12 @@ fiemap_f(
 				break;
 			}
 
-			if ((cur_extent + 1) == max_extents)
+			if (cur_extent == max_extents)
 				break;
 		}
 	}
 
-	if ((cur_extent + 1) == max_extents)
+	if (cur_extent  == max_extents)

                       ^ extra space ;)

Thanks,
-Eric

quoted

 		goto out;
 
 	memset(&st, 0, sizeof(st));