9990-misc-helpers.sh: allow fs type override in fromiso feature.

The overriding feature can be turned on/used by prefixing the file
system type to the path, separated from the device node with a colon.

Example (good override): ext4:/dev/vda49/path/to/grml.iso

If the file system specification contains any non-alphanumerical
characters other than '-' or '_', it will be treated as part of the
actual path, since, at least currently, all known file systems match
this rule.

Example (no override): cra$$$yf§:/dev/sr0/another_path/to/grml.iso

In the former example, no file system type override is detected, which
means that the code will eventually search for a device called
'cra$$$yf§:/dev/sr0' (which, granted, doesn't make a lot of sense).

Sometimes it's necessary or at least handy to specify the file system
used for mounting the fromiso backing device directly.

For instance, putting the ISO file on a RAID1-backed device will fail to
mount it through autodetection (which, really, in most cases is a good
thing to not corrupt the array).

This change also mounts the backing device read-only, which should
enable safe usage and mounting even on RAID1 devices. Note, though, that
read-only mounts are not really very much "read-only", since they
actually sometimes still change on-disk file system metadata, like the
last time the device was mounted).

This said, it should be safe enough and users can easily re-sync the
array to ensure consistency later on.

diff --git a/components/9990-misc-helpers.sh b/components/9990-misc-helpers.sh
index 6f84ead..8551385 100755 (executable)
--- a/components/9990-misc-helpers.sh
+++ b/components/9990-misc-helpers.sh
@@ -139,7 +139,20 @@ check_dev ()
        # support for fromiso=.../isofrom=....
        if [ -n "$FROMISO" ]
        then
-               ISO_DEVICE=$(dirname $FROMISO)
+               fs_type="${FROMISO%%:*}"
+               fs_type_auto='1'
+               ISO_DEVICE="${FROMISO}"
+               if echo "${fs_type}" | grep -q '[^[:alnum:]_-]'; then
+                       # Not a valid file system name. Treat as part of the
+                       # path, and, especially, use autodetection.
+                       fs_type=''
+               else
+                       # Looks like a file system specification, treat it
+                       # like that.
+                       fs_type_auto='0'
+                       ISO_DEVICE="${ISO_DEVICE#*:}"
+               fi
+               ISO_DEVICE=$(dirname "${ISO_DEVICE}")
                if ! [ -b $ISO_DEVICE ]
                then
                        # to support unusual device names like /dev/cciss/c0d0p1
@@ -160,14 +173,17 @@ check_dev ()
                        # example an ISO when booting on an ONIE system
                        if echo "${FROMISO}" | grep -q "\.iso$"
                        then
-                               fs_type=$(get_fstype "${FROMISO}")
+                               if [ '0' -ne "${fs_type_auto}" ]; then
+                                       # Autodetect fs type if not overridden.
+                                       fs_type=$(get_fstype "${FROMISO}")
+                               fi
                                if is_supported_fs ${fs_type}
                                then
                                        mkdir /run/live/fromiso
-                                       mount -t $fs_type "${FROMISO}" /run/live/fromiso
+                                       mount -t "${fs_type}" -o 'ro' "${FROMISO}" '/run/live/fromiso'
                                        if [ "$?" != 0 ]
                                        then
-                                               echo "Warning: unable to mount ${FROMISO}." >>/boot.log
+                                               echo "Warning: unable to mount ${FROMISO} (type ${fs_type})." >>/boot.log
                                        fi
                                        devname="/run/live/fromiso"
                                fi
@@ -175,16 +191,30 @@ check_dev ()
                                echo "Warning: device for bootoption fromiso= ($FROMISO) not found.">>/boot.log
                        fi
                else
-                       fs_type=$(get_fstype "${ISO_DEVICE}")
+                       # Need to extract actual ISO file path later on,
+                       # initialize first.
+                       iso_name="${FROMISO}"
+
+                       if [ '0' -ne "${fs_type_auto}" ]; then
+                               # Try to auto-detect file system if not
+                               # explicitly provided.
+                               fs_type=$(get_fstype "${ISO_DEVICE}")
+                       else
+                               # Delete file system type override.
+                               iso_name="${iso_name#*:}"
+                       fi
+                       # At this point, the backing device should always be
+                       # at the very front, so remove that - leaving only the
+                       # ISO file path.
+                       iso_name="$(echo "${iso_name}" | sed "s|^${ISO_DEVICE}||")"
                        if is_supported_fs ${fs_type}
                        then
                                mkdir /run/live/fromiso
-                               mount -t $fs_type "$ISO_DEVICE" /run/live/fromiso
-                               ISO_NAME="$(echo $FROMISO | sed "s|$ISO_DEVICE||")"
-                               loopdevname=$(setup_loop "/run/live/fromiso/${ISO_NAME}" "loop" "/sys/block/loop*" "" '')
+                               mount -t "${fs_type}" -o 'ro' "$ISO_DEVICE" '/run/live/fromiso'
+                               loopdevname=$(setup_loop "/run/live/fromiso/${iso_name}" "loop" "/sys/block/loop*" "" '')
                                devname="${loopdevname}"
                        else
-                               echo "Warning: unable to mount $ISO_DEVICE." >>/boot.log
+                               echo "Warning: unable to mount $ISO_DEVICE (type ${fs_type})." >>/boot.log
                        fi
                fi
        fi