[PATCH] mkfs: fix blkid probe API violations causing weird output

["Darrick J. Wong" <djwong@kernel.org>]

From: Darrick J. Wong <djwong@kernel.org>

The blkid_do_fullprobe function in libblkid 2.38.1 will try to read the
last 512 bytes off the end of a block device.  If the block device has a
2k LBA size, that read will fail.  blkid_do_fullprobe passes the -EIO
back to the caller (mkfs) even though the API documentation says it
only returns 1, 0, or -1.

Change the "cannot detect existing fs" logic to look for any negative
number.  Otherwise, you get unhelpful output like this:

$ mkfs.xfs -l size=32m -b size=4096 /dev/loop3
mkfs.xfs: Use the -f option to force overwrite.

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
---
 libxfs/topology.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/libxfs/topology.c b/libxfs/topology.c
index 8c6affb4c4e436..96ee74b61b30f5 100644
--- a/libxfs/topology.c
+++ b/libxfs/topology.c
@@ -205,7 +205,8 @@ check_overwrite(
 out:
 	if (pr)
 		blkid_free_probe(pr);
-	if (ret == -1)
+	/* libblkid 2.38.1 lies and can return -EIO */
+	if (ret < 0)
 		fprintf(stderr,
 			_("%s: probe of %s failed, cannot detect "
 			  "existing filesystem.\n"), progname, device);