mkfs.xfs: fix detection of empty devices

We currently fail to detect that a device does indeed not contain any
signature and we are indeed fine to proceed with it due to mishandling
the return value of blkid_do_fullprobe.  Fix that up and add some
better diagnostics of the blkid detection.

from RH bugzilla https://bugzilla.redhat.com/show_bug.cgi?id=561870

# dd if=/dev/zero of=k bs=1MB count=2 seek=20; mkfs.xfs k
# mkfs.xfs: probe of k failed, cannot detect existing filesystem.
# mkfs.xfs: Use the -f option to force overwrite

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Eric Sandeen <sandeen@sandeen.net>

diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
index 9baf116664d6d298b0d24dfbdaaa6cb23ea8e289..2d09e365304eb6825f4929f3a022b322fdcc88ea 100644 (file)
--- a/mkfs/xfs_mkfs.c
+++ b/mkfs/xfs_mkfs.c
@@ -322,24 +322,40 @@ check_overwrite(
        if (!pr)
                goto out;
 
-       if (blkid_probe_enable_partitions(pr, 1))
+       ret = blkid_probe_enable_partitions(pr, 1);
+       if (ret < 0)
                goto out;
 
-       if (blkid_do_fullprobe(pr))
+       ret = blkid_do_fullprobe(pr);
+       if (ret < 0)
                goto out;
 
-       ret = 0;
+       /*
+        * Blkid returns 1 for nothing found and 0 when it finds a signature,
+        * but we want the exact opposite, so reverse the return value here.
+        *
+        * In addition print some useful diagnostics about what actually is
+        * on the device.
+        */
+       if (ret) {
+               ret = 0;
+               goto out;
+       }
+
        if (!blkid_probe_lookup_value(pr, "TYPE", &type, NULL)) {
                fprintf(stderr,
                        _("%s: %s appears to contain an existing "
                        "filesystem (%s).\n"), progname, device, type);
-               ret = 1;
        } else if (!blkid_probe_lookup_value(pr, "PTTYPE", &type, NULL)) {
                fprintf(stderr,
                        _("%s: %s appears to contain a partition "
                        "table (%s).\n"), progname, device, type);
-               ret = 1;
+       } else {
+               fprintf(stderr,
+                       _("%s: %s appears to contain something weird "
+                       "according to blkid\n"), progname, device);
        }
+       ret = 1;
 
 out:
        if (pr)