libblkid: properly reset chain in probe_do_wipe()

The command wipefs is not able to remove all signatures from the
device if the first detected signature is linux raid. The another
superblock signatures are ignored. For example:

  # pvcreate /dev/sdb1
  # mdadm --create md8 --metadata=0.90 --chunk=64 --level=0 \
        --raid-devices=2 /dev/sdb1 /dev/sdb2

  # wipefs -a /dev/sdb1

will delete the linux raid signature only.

Reported-by: Milan Broz <mbroz@redhat.com>
Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/libblkid/src/probe.c b/libblkid/src/probe.c
index 763f75ca011c111d4dbfb42cd561fd6acd622c39..6bd69d39edc5c27713ee7e2adfa5f6cf669212e5 100644 (file)
--- a/libblkid/src/probe.c
+++ b/libblkid/src/probe.c
@@ -388,6 +388,7 @@ void blkid_reset_probe(blkid_probe pr)
                return;
 
        blkid_probe_reset_vals(pr);
+       blkid_probe_set_wiper(pr, 0, 0);
 
        pr->cur_chain = NULL;
 
@@ -989,7 +990,7 @@ int blkid_do_wipe(blkid_probe pr, int dryrun)
                len = sizeof(buf);
 
        DBG(DEBUG_LOWPROBE, printf(
-           "wiping [offset=0x%jx, len=%zd, chain=%s, idx=%d, dryrun=%s]\n",
+           "do_wipe [offset=0x%jx, len=%zd, chain=%s, idx=%d, dryrun=%s]\n",
            offset, len, chn->driver->name, chn->idx, dryrun ? "yes" : "not"));
 
        l = lseek(fd, offset, SEEK_SET);
@@ -1008,10 +1009,23 @@ int blkid_do_wipe(blkid_probe pr, int dryrun)
                if (chn->idx >= 0) {
                        chn->idx--;
                        DBG(DEBUG_LOWPROBE,
-                               printf("wipe: moving %s chain index to %d\n",
+                               printf("do_wipe: moving %s chain index to %d\n",
                                chn->driver->name,
                                chn->idx));
                }
+               if (chn->idx == -1) {
+                       /* blkid_do_probe() goes to the next chain if the index
+                        * of the current chain is -1, so we have to set the
+                        * chain pointer to the previos chain.
+                        */
+                       size_t idx = chn->driver->id > 0 ?
+                                       chn->driver->id - 1 : 0;
+
+                       if (idx > 0)
+                               pr->cur_chain = &pr->chains[idx];
+                       else if (idx == 0)
+                               pr->cur_chain = NULL;
+               }
        }
        return 0;
 }
@@ -1579,8 +1593,9 @@ size_t blkid_rtrim_whitespace(unsigned char *str)
  * for later resolution to conflicts between superblocks.
  *
  * For example we found valid LVM superblock, LVM wipes 8KiB at the begin of
- * the device. If we found another signature (for example MBR) this wiped area
- * then the signature has been added later and LVM superblock should be ignore.
+ * the device. If we found another signature (for example MBR) within the
+ * wiped area then the signature has been added later and LVM superblock
+ * should be ignore.
  *
  * Note that this heuristic is not 100% reliable, for example "pvcreate --zero
  * n" allows to keep the begin of the device unmodified. It's probably better
@@ -1588,6 +1603,16 @@ size_t blkid_rtrim_whitespace(unsigned char *str)
  * than for conflicts between filesystem superblocks -- existence of unwanted
  * partition table is very unusual, because PT is pretty visible (parsed and
  * interpreted by kernel).
+ *
+ * Note that we usually expect only one signature on the device, it means that
+ * we have to remember only one wiped area from previously successfully
+ * detected signature.
+ *
+ * blkid_probe_set_wiper() -- defines wiped area (e.g. LVM)
+ * blkid_probe_use_wiper() -- try to use area (e.g. MBR)
+ *
+ * Note that there is not relation between _wiper and blkid_to_wipe().
+ *
  */
 void blkid_probe_set_wiper(blkid_probe pr, blkid_loff_t off, blkid_loff_t size)
 {
@@ -1638,12 +1663,17 @@ int blkid_probe_is_wiped(blkid_probe pr, struct blkid_chain **chn,
        return 0;
 }
 
+/*
+ *  Try to use any area -- if the area has been previously wiped then the
+ *  previous probing result should be ignored (reseted).
+ */
 void blkid_probe_use_wiper(blkid_probe pr, blkid_loff_t off, blkid_loff_t size)
 {
        struct blkid_chain *chn = NULL;
 
        if (blkid_probe_is_wiped(pr, &chn, off, size) && chn) {
-               DBG(DEBUG_LOWPROBE, printf("wiped area detected -- ignore previous results\n"));
+               DBG(DEBUG_LOWPROBE, printf("previously wiped area modified "
+                                      " -- ignore previous results\n"));
                blkid_probe_set_wiper(pr, 0, 0);
                blkid_probe_chain_reset_vals(pr, chn);
        }