Open pools asynchronously after module load

One of the side effects of calling zvol_create_minors() in
zvol_init() is that all pools listed in the cache file will
be opened.  Depending on the state and contents of your pool
this operation can take a considerable length of time.

Doing this at load time is undesirable because the kernel
is holding a global module lock.  This prevents other modules
from loading and can serialize an otherwise parallel boot
process.  Doing this after module inititialization also
reduces the chances of accidentally introducing a race
during module init.

To ensure that /dev/zvol/<pool>/<dataset> devices are
still automatically created after the module load completes
a udev rules has been added.  When udev notices that the
/dev/zfs device has been create the 'zpool list' command
will be run.  This then will cause all the pools listed
in the zpool.cache file to be opened.

Because this process in now driven asynchronously by udev
there is the risk of problems in downstream distributions.

Signed-off-by: Brian Behlendorf <[email protected]>
Issue #756
Issue #1020
Issue #1234

3 files changed, 5 insertions, 4 deletions

diff --git a/module/zfs/zvol.c b/module/zfs/zvol.c
index 97b65c815..e35c91bc1 100644
--- a/module/zfs/zvol.c
+++ b/module/zfs/zvol.c
@@ -1582,8 +1582,6 @@ zvol_init(void)
 	blk_register_region(MKDEV(zvol_major, 0), 1UL << MINORBITS,
 	                    THIS_MODULE, zvol_probe, NULL, NULL);
 
-	(void) zvol_create_minors(NULL);
-
 	return (0);
 
 out2:
diff --git a/scripts/zconfig.sh b/scripts/zconfig.sh
index 141348c03..281166c59 100755
--- a/scripts/zconfig.sh
+++ b/scripts/zconfig.sh
@@ -264,8 +264,9 @@ test_4() {
 	zconfig_zvol_device_stat 0 ${POOL_NAME} ${FULL_ZVOL_NAME} \
 	    ${FULL_SNAP_NAME} ${FULL_CLONE_NAME} || fail 9
 
-	# Load the modules, wait 1 second for udev
+	# Load the modules, list the pools to ensure they are opened
 	${ZFS_SH} zfs="spa_config_path=${TMP_CACHE}" || fail 10
+	${ZPOOL} list &>/dev/null
 
 	# Verify the devices were created
 	zconfig_zvol_device_stat 10 ${POOL_NAME} ${FULL_ZVOL_NAME} \
diff --git a/udev/rules.d/90-zfs.rules.in b/udev/rules.d/90-zfs.rules.in
index 52e1d6393..a2715d2e7 100644
--- a/udev/rules.d/90-zfs.rules.in
+++ b/udev/rules.d/90-zfs.rules.in
@@ -1,4 +1,4 @@
-SUBSYSTEM!="block", GOTO="zfs_end"
+SUBSYSTEM!="block|misc", GOTO="zfs_end"
 ACTION!="add|change", GOTO="zfs_end"
 
 ENV{ID_FS_TYPE}=="zfs", RUN+="/sbin/modprobe zfs"
@@ -7,4 +7,6 @@ ENV{ID_FS_TYPE}=="zfs_member", RUN+="/sbin/modprobe zfs"
 KERNEL=="null", SYMLINK+="root"
 SYMLINK=="null", SYMLINK+="root"
 
+SUBSYSTEM=="misc", KERNEL=="zfs", RUN+="@sbindir@/zpool list"
+
 LABEL="zfs_end"