OpenZFS 8961 - SPA load/import should tell us why it failed

Problem
=======

When we fail to open or import a storage pool, we typically don't
get any additional diagnostic information, just "no pool found" or
"can not import".

While there may be no additional user-consumable information, we should
at least make this situation easier to debug/diagnose for developers
and support.  For example, we could start by using `zfs_dbgmsg()`
to log each thing that we try when importing, and which things
failed. E.g. "tried uberblock of txg X from label Y of device Z". Also,
we could log each of the stages that we go through in `spa_load_impl()`.

Solution
========

Following the cleanup to `spa_load_impl()`, debug messages have been
added to every point of failure in that function. Additionally,
debug messages have been added to strategic places, such as
`vdev_disk_open()`.

Authored by: Pavel Zakharov <[email protected]>
Reviewed by: George Wilson <[email protected]>
Reviewed by: Matthew Ahrens <[email protected]>
Reviewed by: Andrew 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/8961
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/418079e0
Closes #7459

1 files changed, 2 insertions, 0 deletions

diff --git a/include/sys/spa.h b/include/sys/spa.h
index 89f4f5107..1172468ad 100644
--- a/include/sys/spa.h
+++ b/include/sys/spa.h
@@ -985,6 +985,8 @@ extern uint64_t spa_deadman_synctime(spa_t *spa);
 extern uint64_t spa_deadman_ziotime(spa_t *spa);
 
 /* Miscellaneous support routines */
+extern void spa_load_failed(spa_t *spa, const char *fmt, ...);
+extern void spa_load_note(spa_t *spa, const char *fmt, ...);
 extern void spa_activate_mos_feature(spa_t *spa, const char *feature,
     dmu_tx_t *tx);
 extern void spa_deactivate_mos_feature(spa_t *spa, const char *feature);