[PATCH] filefrag: count optimize non-verbose mode; count 0 extents properly when verbose

[Eric Sandeen <sandeen@redhat.com>]

# rm -f a; touch a; filefrag -v a

yields 1 extent when it should be 0.  Without -v, 0 is returned.

Fix this up by special-casing no extents returned in verbose
mode; skip printing the header for the columns too, since there
are no columns to print.

Also, in nonverbose mode we can set fm_extent_count to 0
so that FIEMAP will just query the extent count without gathering
details; as it is today I think a non-verbose query may under-report
the extent count once "count" extents have been filled in.

Addresses-redhat-bugzilla: 653234
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
---

diff --git a/misc/filefrag.c b/misc/filefrag.c
index bd4486d..a48b9b0 100644
--- a/misc/filefrag.c
+++ b/misc/filefrag.c
@@ -194,7 +194,14 @@ static int filefrag_fiemap(int fd, int blk_shift, int *num_extents)
 	do {
 		fiemap->fm_length = ~0ULL;
 		fiemap->fm_flags = flags;
-		fiemap->fm_extent_count = count;
+		/*
+		 * If fm_extent_count == 0, FIEMAP returns count of
+		 * extents found without filling in details.
+		 */
+		if (!verbose)
+			fiemap->fm_extent_count = 0;
+		else
+			fiemap->fm_extent_count = count;
 		rc = ioctl(fd, FS_IOC_FIEMAP, (unsigned long) fiemap);
 		if (rc < 0) {
 			if (errno == EBADR && fiemap_incompat_printed == 0) {
@@ -206,6 +213,14 @@ static int filefrag_fiemap(int fd, int blk_shift, int *num_extents)
 		}
 
 		if (verbose && !fiemap_header_printed) {
+			/*
+			 * No extents on first call?
+			 * Skip header and show 0 extents.
+			 */
+			if (fiemap->fm_mapped_extents == 0) {
+				*num_extents = 0;
+				goto out;
+			}
 			printf(" ext %*s %*s %*s length flags\n", logical_width,
 			       "logical", physical_width, "physical",
 			       physical_width, "expected");