From: Christoph Hellwig <hch@lst.de>
Date: Fri, 5 Feb 2010 07:52:52 +0000 (+0100)
Subject: mkfs.xfs: fix detection of empty devices
X-Git-Url: http://git.kernel.org/?p=fs%2Fxfs%2Fxfsprogs-dev.git;a=commitdiff_plain;h=c2b707cf506c83ad4ab38c97c11cf358cc0bec88

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 9baf116..2d09e36 100644
--- 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)