Initramfs scripts for ZoL.

* Supports booting of a ZFS snapshot.
  Do this by cloning the snapshot into a dataset. If this, the resulting
  dataset, already exists, destroy it. Then mount it on root.
  * If snapshot does not exist, use base dataset (the part before '@')
    as boot filesystem instead.
  * If no snapshot is specified on the 'root=' kernel command line, but there
    is an '@', then get a list of snapshots below that filesystem and ask the
    user which to use.
  * Clone with 'mountpoint=none' and 'canmount=noauto' - we mount manually
    and explicitly.
    * For sub-filesystems, that doesn't have a mountpoint property set, we use
      the 'org.zol:mountpoint' to keep track of it's mountpoint.
  * Allow rollback of snapshots instead of clone it and boot from the clone.
* Allow mounting a root- and subfs with mountpoint=legacy set
* Allow mounting a filesystem which is using nativ encryption.
* Support all currently used kernel command line arguments
  All the different distributions have their own standard on what to specify
  on the kernel command line to boot of a ZFS filesystem.
  * Extra options:
    * zfsdebug=(on,yes,1)	Show extra debugging information
    * zfsforce=(on,yes,1)	Force import the pool
    * rollback=(on,yes,1)	Rollback (instead of clone) the snapshot
* Only try to import pool if it haven't already been imported
  * This will negate the need to force import a pool that have not been exported cleanly.
  * Support exclusion of pools to import by setting ZFS_POOL_EXCEPTIONS in /etc/default/zfs.
* Support additional configuration variable ZFS_INITRD_ADDITIONAL_DATASETS
  to mount additional filesystems not located under your root dataset.
* Include /etc/modprobe.d/{zfs,spl}.conf in the initrd if it/they exist.
* Include the udev rule to use by-vdev for pool imports.
* Include the /etc/default/zfs file to the initrd.
* Only try /dev/disk/by-* in the initrd if USE_DISK_BY_ID is set.
  * Use /dev/disk/by-vdev before anything.
  * Add /dev as a last ditch attempt.
  * Fallback to using the cache file if that exist if nothing else worked.
* Use /sbin/modprobe instead of built-in (BusyBox) modprobe.
  This gets rid of the message "modprobe: can't load module zcommon".
  Thanx to pcoultha for finding this.

Signed-off-by: Turbo Fredriksson <turbo@bayour.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2116
Closes #2114

contrib/initramfs/hooks/zfs

@@ -0,0 +1,103 @@
+#!/bin/sh
+#
+# Add ZoL filesystem capabilities to an initrd, usually for a native ZFS root.
+#
+
+# This hook installs udev rules for ZoL.
+PREREQ="zdev"
+
+# These prerequisites are provided by the zfsutils package. The zdb utility is
+# not strictly required, but it can be useful at the initramfs recovery prompt.
+COPY_EXEC_LIST="/sbin/zdb /sbin/zpool /sbin/zfs /sbin/mount.zfs"
+COPY_EXEC_LIST="$COPY_EXEC_LIST /usr/bin/dirname"
+COPY_FILE_LIST="/etc/hostid /etc/zfs/zpool.cache /etc/default/zfs"
+COPY_FILE_LIST="$COPY_FILE_LIST /etc/zfs/zfs-functions /etc/zfs/vdev_id.conf"
+COPY_FILE_LIST="$COPY_FILE_LIST /lib/udev/rules.d/69-vdev.rules"
+
+# These prerequisites are provided by the base system.
+COPY_EXEC_LIST="$COPY_EXEC_LIST /bin/hostname /sbin/blkid"
+
+# Explicitly specify all kernel modules because automatic dependency resolution
+# is unreliable on many systems.
+BASE_MODULES="zlib_deflate spl zavl zcommon znvpair zunicode zfs"
+CRPT_MODULES="sun-ccm sun-gcm sun-ctr"
+MANUAL_ADD_MODULES_LIST="$BASE_MODULES"
+
+# Generic result code.
+RC=0
+
+case $1 in
+prereqs)
+	echo "$PREREQ"
+	exit 0
+	;;
+esac
+
+for ii in $COPY_EXEC_LIST
+do
+	if [ ! -x "$ii" ]
+	then
+		echo "Error: $ii is not executable."
+		RC=2
+	fi
+done
+
+if [ "$RC" -ne 0 ]
+then
+	exit "$RC"
+fi
+
+. /usr/share/initramfs-tools/hook-functions
+
+mkdir -p "$DESTDIR/etc/"
+
+# ZDB uses pthreads for some functions, but the library dependency is not
+# automatically detected. The `find` utility and extended `cp` options are
+# used here because libgcc_s.so could be in a subdirectory of /lib for
+# multi-arch installations.
+cp --target-directory="$DESTDIR" --parents $(find /lib -type f -name libgcc_s.so.1)
+
+for ii in $COPY_EXEC_LIST
+do
+	copy_exec "$ii"
+done
+
+for ii in $COPY_FILE_LIST
+do
+	dir=$(dirname "$ii")
+	[ -d "$dir" ] || mkdir -p "$dir"
+	[ -f "$ii" ] && cp -p "$ii" "$DESTDIR/$ii"
+done
+
+for ii in $MANUAL_ADD_MODULES_LIST
+do
+	manual_add_modules "$ii"
+done
+
+if [ -f "/etc/hostname" ]
+then
+	cp -p "/etc/hostname" "$DESTDIR/etc/"
+else
+	hostname >"$DESTDIR/etc/hostname"
+fi
+
+for ii in zfs zfs.conf spl spl.conf
+do  
+	if [ -f "/etc/modprobe.d/$ii" ]; then
+		if [ ! -d "$DESTDIR/etc/modprobe.d" ]; then
+			mkdir -p $DESTDIR/etc/modprobe.d
+		fi
+		cp -p "/etc/modprobe.d/$ii" $DESTDIR/etc/modprobe.d/
+	fi
+done
+
+# With pull request #1476 (not yet merged) comes a verbose warning
+# if /usr/bin/net doesn't exist or isn't executable. Just create
+# a dummy...
+[ ! -d "$DESTDIR/usr/bin" ] && mkdir -p "$DESTDIR/usr/bin"
+if [ ! -x "$DESTDIR/usr/bin/net" ]; then
+    touch "$DESTDIR/usr/bin/net"
+    chmod +x "$DESTDIR/usr/bin/net"
+fi
+
+exit 0