Improve `zpool labelclear`

1) As implemented the `zpool labelclear` command overwrites
the calculated offsets of all four vdev labels even when only a
single valid label is found.  If the device as been re-purposed
but still contains a valid label this can result in space no
longer owned by ZFS being zeroed.  Prevent this by verifying
every label removed is intact before it's overwritten.

2) Address a small bug in zpool_do_labelclear() which prevented
labelclear from working on file vdevs.  Only block devices support
BLKFLSBUF, try the ioctl() but when it's reported as unsupported
this should not be fatal.

3) Fix `zpool labelclear` so it can be run on vdevs which were
removed from the pool with `zpool remove`.  Additionally, allow
intact but partial labels to be cleared as in the case of a failed
`zpool attach` or `zpool replace`.

4) Remove LABELCLEAR and LABELREAD variables for test cases.

Reviewed-by: Matt Ahrens <[email protected]>
Reviewed-by: Tim Chase <[email protected]>
Reviewed-by: Tony Hutter <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #8500 
Closes #8373 
Closes #6261 

1 files changed, 8 insertions, 3 deletions

diff --git a/cmd/zpool/zpool_main.c b/cmd/zpool/zpool_main.c
index 61403a173..3607656e0 100644
--- a/cmd/zpool/zpool_main.c
+++ b/cmd/zpool/zpool_main.c
@@ -1113,13 +1113,18 @@ zpool_do_labelclear(int argc, char **argv)
 		return (1);
 	}
 
-	if (ioctl(fd, BLKFLSBUF) != 0)
+	/*
+	 * Flush all dirty pages for the block device.  This should not be
+	 * fatal when the device does not support BLKFLSBUF as would be the
+	 * case for a file vdev.
+	 */
+	if ((ioctl(fd, BLKFLSBUF) != 0) && (errno != ENOTTY))
 		(void) fprintf(stderr, gettext("failed to invalidate "
 		    "cache for %s: %s\n"), vdev, strerror(errno));
 
-	if (zpool_read_label(fd, &config, NULL) != 0 || config == NULL) {
+	if (zpool_read_label(fd, &config, NULL) != 0) {
 		(void) fprintf(stderr,
-		    gettext("failed to check state for %s\n"), vdev);
+		    gettext("failed to read label from %s\n"), vdev);
 		ret = 1;
 		goto errout;
 	}