OpenZFS 8962 - zdb should work on non-idle pools

Currently `zdb` consistently fails to examine non-idle pools as it
fails during the `spa_load()` process. The main problem seems to be
that `spa_load_verify()` fails as can be seen below:

    $ sudo zdb -d -G dcenter
    zdb: can't open 'dcenter': I/O error

    ZFS_DBGMSG(zdb):
    spa_open_common: opening dcenter
    spa_load(dcenter): LOADING
    disk vdev '/dev/dsk/c4t11d0s0': best uberblock found for spa dcenter. txg 40824950
    spa_load(dcenter): using uberblock with txg=40824950
    spa_load(dcenter): UNLOADING
    spa_load(dcenter): RELOADING
    spa_load(dcenter): LOADING
    disk vdev '/dev/dsk/c3t10d0s0': best uberblock found for spa dcenter. txg 40824952
    spa_load(dcenter): using uberblock with txg=40824952
    spa_load(dcenter): FAILED: spa_load_verify failed [error=5]
    spa_load(dcenter): UNLOADING

This change makes `spa_load_verify()` a dryrun when ran from
`zdb`. This is done by creating a global flag in zfs and then setting
it in `zdb`.

Authored by: Pavel Zakharov <[email protected]>
Reviewed by: George Wilson <[email protected]>
Reviewed by: Matthew Ahrens <[email protected]>
Reviewed by: Andy Stormont <[email protected]>
Approved by: Dan McDonald <[email protected]>
Ported-by: Tim Chase <[email protected]>
Signed-off-by: Tim Chase <[email protected]>

OpenZFS-issue: https://illumos.org/issues/8962
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/180ad792
Closes #7459

1 files changed, 18 insertions, 2 deletions

diff --git a/module/zfs/spa.c b/module/zfs/spa.c
index a17da4239..80f0c6f36 100644
--- a/module/zfs/spa.c
+++ b/module/zfs/spa.c
@@ -170,6 +170,12 @@ uint_t		zio_taskq_basedc = 80;		/* base duty cycle */
 boolean_t	spa_create_process = B_TRUE;	/* no process ==> no sysdc */
 
 /*
+ * Report any spa_load_verify errors found, but do not fail spa_load.
+ * This is used by zdb to analyze non-idle pools.
+ */
+boolean_t	spa_load_verify_dryrun = B_FALSE;
+
+/*
  * This (illegal) pool name is used when temporarily importing a spa_t in order
  * to get the vdev stats associated with the imported devices.
  */
@@ -2140,8 +2146,15 @@ spa_load_verify(spa_t *spa)
 	spa->spa_load_meta_errors = sle.sle_meta_count;
 	spa->spa_load_data_errors = sle.sle_data_count;
 
-	if (!error && sle.sle_meta_count <= policy.zrp_maxmeta &&
-	    sle.sle_data_count <= policy.zrp_maxdata) {
+	if (sle.sle_meta_count != 0 || sle.sle_data_count != 0) {
+		spa_load_note(spa, "spa_load_verify found %llu metadata errors "
+		    "and %llu data errors", (u_longlong_t)sle.sle_meta_count,
+		    (u_longlong_t)sle.sle_data_count);
+	}
+
+	if (spa_load_verify_dryrun ||
+	    (!error && sle.sle_meta_count <= policy.zrp_maxmeta &&
+	    sle.sle_data_count <= policy.zrp_maxdata)) {
 		int64_t loss = 0;
 
 		verify_ok = B_TRUE;
@@ -2159,6 +2172,9 @@ spa_load_verify(spa_t *spa)
 		spa->spa_load_max_txg = spa->spa_uberblock.ub_txg;
 	}
 
+	if (spa_load_verify_dryrun)
+		return (0);
+
 	if (error) {
 		if (error != ENXIO && error != EIO)
 			error = SET_ERROR(EIO);