Add functionality that exists in initramfs to dracut.

* Support 'zfs:<rootfs>' import and mounting.
  This was for some reason removed in eda3d4e.
* Support booting from snapshots.
* Support mounting recursive filesystems.
* Support mounting of additional filesystems.
* Support mounting nativly encrypted filesystems.

* Move code snippet that fetches and mounts recursive filesystems into recursive_mount_filesystems().
* zfs_set_ifs() needs to be a global func. We need it in a number of places!
  * Use this wherever we use CMD="somecmd someopt someopt" ; OUT="$($CMD someopt)"
* Dracut have the func emergency_shell() which does a little more.
  For those that don't have it, just run '/bin/sh -i -l'.

contrib/dracut/90zfs/mount-zfs.sh.in

@@ -15,29 +15,58 @@ esac
 udev_trigger
 
 if [ "${root}" = "zfs:AUTO" ] ; then
-	ZFS_BOOTFS=""
 	POOLS=$(get_pools)
 	IFS=";"
+
 	for pool in $POOLS
 	do
 		[ -z "$pool" ] && continue
+		ZFS_BOOTFS=""
 
 		# No 'else' or return below - if there's more pools, we try
 		# them. If not, we'll drop through and go to the end
 		# where we need a reboot because we couldn't find a root fs.
-		if import_pool "$pool"; then
-			if find_rootfs "$pool"; then
-				if mount_fs "${ZFS_BOOTFS}"; then
-					info "ZFS: Using ${ZFS_BOOTFS} as root."
-
-					rootok=1
+		if zfs_action "Importing pool ${pool}" import_pool "${pool}"
+		then
+			if find_rootfs "${pool}"; then
+				if recursive_mount_filesystems \
+				    "Using '${ZFS_BOOTFS}' as root." \
+				    "${ZFS_BOOTFS}"
+				then
 					IFS="$OLD_IFS"
-
+					rootok=1
 					return 0
 				fi
 			fi
 		fi
 	done
+else
+	# Because of the case at the top, it's either 'zfs:AUTO' or
+	# 'zfs:<rootfs>'. Import the pool from rootfs and mount it.
+	root="${root#zfs:}"	# Remove leading 'zfs:'
+	pool="${root%%/*}"	# Remove everything after first slash.
+	ZFS_BOOTFS="${root}"	# For zfs-functions.
+	if zfs_action "Importing pool ${pool}" import_pool "${pool}"; then
+		info "ZFS: Using ${pool} as root pool."
+
+		# Will be overwritten in clone_snap() if we're booting from
+		# a snapshot.
+		ZFS_BOOTFS_ORIG="$ZFS_BOOTFS"
+
+		# Booting from a snapshot? Updates ZFS_BOOTFS_ORIG and ZFS_BOOTFS...
+		echo "${root}" | grep -q '@' && setup_snapshot_booting
+		root="$ZFS_BOOTFS"
+
+		if recursive_mount_filesystems "Using '${root}' as root." \
+		    "${root}"
+		then
+			rootok=1
+			return 0
+		fi
+	else
+		warn "ZFS: Can't import '${pool}'."
+		# Fallthrough
+	fi
 fi
 
 rootok=0

contrib/dracut/README.dracut.markdown

@@ -42,6 +42,31 @@ parameters passed in from the boot loader:
 * `root=...`: If not set, importable pools are searched for a bootfs
 attribute.  If an explicitly set root is desired, you may use
 `root=ZFS:pool/dataset`
+  * It is also possible to boot from a snapshot (technically, a clone of
+    the snapshot) using `root=ZFS:pool/dataset@snapshot`.
+  * If the actual snapshot isn't specified, only the at (@) character,
+    the user will be asked for a snapshot to boot from.
+  * With the extra parameter `rollback=(on,yes,1)`, instead of doing a
+    clone and boot from that, the code will rollback the filesystem up
+    to the snapshot specified.
+  * Even though there is no freely availible native encryption for any
+    opensource ZFS implementation, the hope is that one day have one.
+    This code supports the native encryption that Solaris have, using
+    the `zfs key` option.
+  * Supports both 'native' and 'legacy' filesystems.
+  * Supports 'recursive filesystems'. That is, if the root file system
+    is something like `rpool/ROOT/fedora17`, it is possible to have
+    `rpool/ROOT/fedora17/var`, `rpool/ROOT/fedora17/usr` etc.
+    It is not important that the 'mountpoint' property is set or correct,
+    the 'base filesystem' will be removed from the full path of the filesystem.
+    This means, that with the root fs as `rpool/ROOT/fedora17` and the sub-
+    filesystem as `rpool/ROOT/fedora17/var`, the result would be `/var`,
+    where it will be mounted.
+  * In addition to 'recursive filesystems', it is possible to have other
+    filesystems mounted by setting the ZFS_INITRD_ADDITIONAL_DATASETS variable
+    in /etc/sysconfig/zfs. Here, it is imparative that the 'mountpoint'
+    property is correct for each of these filesystems, since each filesystem
+    will use this to correctly mount it.
 
 * `zfs_force=0`: If set to 1, the initramfs will run `zpool import -f` when
 attempting to import pools if the required pool isn't automatically imported

contrib/initramfs/scripts/zfs

@@ -335,13 +335,8 @@ mountroot()
 	#   NOTE: Mounted in the order specified in the
 	#         ZFS_INITRD_ADDITIONAL_DATASETS variable so take care!
 
-	# Go through the complete list (recursivly) of all filesystems below
-	# the real root dataset
-	filesystems=$("${ZFS}" list -oname -tfilesystem -H -r "${ZFS_BOOTFS}")
-	for fs in $filesystems $ZFS_INITRD_ADDITIONAL_DATASETS
-	do
-		mount_fs "$fs"
-	done
+	recursive_mount_filesystems "Using ${ZFS_BOOTFS} as root." \
+	    "${ZFS_BOOTFS}"
 
 	# ------------
 	# Debugging information