[PATCH V2] mkfs: fix mkfs.xfs -dfile,name=$NAME for new files

[Eric Sandeen <sandeen@xxxxxxxxxxx>]

# /sbin/mkfs.xfs -dfile,name=grrr,size=100g
mkfs.xfs: Use the -f option to force overwrite.

check_overwrite is failing, because  blkid_new_probe_from_filename()
is failing, because the (new) image file is 0 length.

It's easy to test for 0 length, and if found, there is
nothing to overwrite so return 0.

Also, if testing itself failed for some reason, print 
a message to that effect:

# mkfs/mkfs.xfs -dfile,name=newfile,size=1g
mkfs.xfs: probe of newfile failed, cannot detect existing filesystem.
mkfs.xfs: Use the -f option to force overwrite.

Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxxx>
---


diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
index faaafed..b6801dd 100644
--- a/mkfs/xfs_mkfs.c
+++ b/mkfs/xfs_mkfs.c
@@ -283,27 +283,47 @@ calc_stripe_factors(
 }
 
 #ifdef ENABLE_BLKID
+/*
+ * Check for existing filesystem or partition table on device.
+ * Returns:
+ *      1 for existing fs or partition
+ *      0 for nothing found
+ *     -1 for internal error
+ */
 static int
 check_overwrite(
        char            *device)
 {
        const char      *type;
-       blkid_probe     pr;
-       int             ret = 0;
+       blkid_probe     pr = NULL;
+       int             ret;
+       struct stat     statbuf;
 
        if (!device || !*device)
                return 0;
 
+       ret = -1; /* will reset on success of all setup calls */
+
+       if (stat(device, &statbuf) < 0)
+               goto out;
+
+       /* nothing to overwrite on a 0-length device */
+       if (statbuf.st_size == 0) {
+               ret = 0;
+               goto out;
+       }
+
        pr = blkid_new_probe_from_filename(device);
        if (!pr)
-               return -1;
+               goto out;
 
        if (blkid_probe_enable_partitions(pr, 1))
-               goto out_free_probe;
+               goto out;
 
        if (blkid_do_fullprobe(pr))
-               goto out_free_probe;
+               goto out;
 
+       ret = 0;
        if (!blkid_probe_lookup_value(pr, "TYPE", &type, NULL)) {
                fprintf(stderr,
                        _("%s: %s appears to contain an existing "
@@ -316,8 +336,13 @@ check_overwrite(
                ret = 1;
        }
 
-out_free_probe:
-       blkid_free_probe(pr);
+out:
+       if (pr)
+               blkid_free_probe(pr);
+       if (ret == -1)
+               fprintf(stderr,
+                       _("%s: probe of %s failed, cannot detect "
+                         "existing filesystem.\n"), progname, device);
        return ret;
 }