Call zvol_create_minors() in spa_open_common() when initializing pool

There is an extremely odd bug that causes zvols to fail to appear on
some systems, but not others. Recently, I was able to consistently
reproduce this issue over a period of 1 month. The issue disappeared
after I applied this change from FreeBSD.

This is from FreeBSD's pool version 28 import, which occurred in
revision 219089.

Ported-by: Richard Yao <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Issue #441
Issue #599

module/zfs/spa.c

@@ -64,6 +64,7 @@
 #include <sys/zfs_ioctl.h>
 #include <sys/dsl_scan.h>
 #include <sys/zfeature.h>
+#include <sys/zvol.h>
 
 #ifdef	_KERNEL
 #include <sys/bootprops.h>
@@ -2856,6 +2857,7 @@ spa_open_common(const char *pool, spa_t **spapp, void *tag, nvlist_t *nvpolicy,
 	spa_load_state_t state = SPA_LOAD_OPEN;
 	int error;
 	int locked = B_FALSE;
+	int firstopen = B_FALSE;
 
 	*spapp = NULL;
 
@@ -2879,6 +2881,8 @@ spa_open_common(const char *pool, spa_t **spapp, void *tag, nvlist_t *nvpolicy,
 	if (spa->spa_state == POOL_STATE_UNINITIALIZED) {
 		zpool_rewind_policy_t policy;
 
+		firstopen = B_TRUE;
+
 		zpool_get_rewind_policy(nvpolicy ? nvpolicy : spa->spa_config,
 		    &policy);
 		if (policy.zrp_request & ZPOOL_DO_REWIND)
@@ -2953,6 +2957,11 @@ spa_open_common(const char *pool, spa_t **spapp, void *tag, nvlist_t *nvpolicy,
 		mutex_exit(&spa_namespace_lock);
 	}
 
+#ifdef _KERNEL
+	if (firstopen)
+		zvol_create_minors(spa->spa_name);
+#endif
+
 	*spapp = spa;
 
 	return (0);
@@ -4010,6 +4019,10 @@ spa_import(const char *pool, nvlist_t *config, nvlist_t *props, uint64_t flags)
 	mutex_exit(&spa_namespace_lock);
 	spa_history_log_version(spa, LOG_POOL_IMPORT);
 
+#ifdef _KERNEL
+	zvol_create_minors(pool);
+#endif
+
 	return (0);
 }
 

module/zfs/zfs_ioctl.c

@@ -1268,9 +1268,6 @@ zfs_ioc_pool_import(zfs_cmd_t *zc)
 			error = err;
 	}
 
-	if (error == 0)
-		zvol_create_minors(zc->zc_name);
-
 	nvlist_free(config);
 
 	if (props)