Illumos 3749 - zfs event processing should work on R/O root filesystems

3749 zfs event processing should work on R/O root filesystems
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Eric Schrock <eric.schrock@delphix.com>
Approved by: Christopher Siden <christopher.siden@delphix.com>

References:
  https://www.illumos.org/issues/3749
  https://github.com/illumos/illumos-gate/commit/3cb69f7

Porting notes:
- [include/sys/spa_impl.h]
  - ffe9d38 Add generic errata infrastructure
  - 1421c89 Add visibility in to arc_read
- [include/sys/fm/fs/zfs.h]
  - 2668527 Add linux events
  - 6283f55 Support custom build directories and move includes
- [module/zfs/spa_config.c]
  - Updated spa_config_sync() to match illumos with the exception
    of a Linux specific block.

Ported-by: kernelOfTruth kerneloftruth@gmail.com
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

include/sys/fm/fs/zfs.h

@@ -56,6 +56,7 @@ extern "C" {
 #define	FM_EREPORT_ZFS_IO_FAILURE		"io_failure"
 #define	FM_EREPORT_ZFS_PROBE_FAILURE		"probe_failure"
 #define	FM_EREPORT_ZFS_LOG_REPLAY		"log_replay"
+#define	FM_EREPORT_ZFS_CONFIG_CACHE_WRITE	"config_cache_write"
 #define	FM_EREPORT_ZFS_RESILVER_START		"resilver.start"
 #define	FM_EREPORT_ZFS_RESILVER_FINISH		"resilver.finish"
 #define	FM_EREPORT_ZFS_SCRUB_START		"scrub.start"

include/sys/spa_impl.h

@@ -252,6 +252,7 @@ struct spa {
 	uint64_t	spa_deadman_synctime;	/* deadman expiration timer */
 	uint64_t	spa_errata;		/* errata issues detected */
 	spa_stats_t	spa_stats;		/* assorted spa statistics */
+	hrtime_t	spa_ccw_fail_time;	/* Conf cache write fail time */
 
 	/*
 	 * spa_refcount & spa_config_lock must be the last elements