[arch-releng] [PATCH] archiso_loop_mnt - cleaner boot from loopmounted iso file

[Adam Purkrt]

On 07/12/2015 02:29 AM, Gerardo Exequiel Pozzi wrote:
> On 07/11/2015 04:00 PM, Adam Purkrt wrote:
>> I would like to suggest the patch below, to archiso_loop_mnt hook.
>>
>> Currently, when booting loopmounted iso file, it is necessary to
>> specify not only img_dev and img_loop (which should be sufficient),
>> but also archisolabel or archisodevice. With the patch, archisodevice
>> is directly populated with the correct loop device, and it is not
>> necessary to specify the label when booting from loopmounted iso,
>> which makes for leaner and cleaner grub.cfg.
>>
>> The kernel command line in grub.cfg currently needed:
>>
>> linux (loop)/arch/boot/x86_64/vmlinuz archisolabel=ARCH_201507
>> img_dev=$imgdevpath img_loop=$isofile earlymodules=loop
>>
>> after the patch:
>>
>> linux (loop)/arch/boot/x86_64/vmlinuz img_dev=$imgdevpath
>> img_loop=$isofile earlymodules=loop
>>
> You are right!
>
> Please also update the README.altbootmethods ;)
>
> PS: "earlymodules=loop": Is like a copy&paste hurricane from old age.
> It was a temporal workaround (2011.08.19), but spread across all places.
>
> Thanks.
>

It's good that "earlymodules=loop" is not necessary, thanks for pointing it out.

Updated the README.altbootmethods, using uuid over label. Overall the patch is:

diff --git a/archiso/initcpio/hooks/archiso_loop_mnt b/archiso/initcpio/hooks/archiso_loop_mnt
index 46338e5..f95a47d 100644
--- a/archiso/initcpio/hooks/archiso_loop_mnt
+++ b/archiso/initcpio/hooks/archiso_loop_mnt
@@ -18,7 +18,9 @@ archiso_loop_mount_handler () {
         echo $(readlink -f ${img_dev}) >> /run/archiso/used_block_devices
     fi
 
-    if ! _dev_loop=$(losetup --find --show --read-only "/run/archiso/img_dev/${img_loop}"); then
+    if _dev_loop=$(losetup --find --show --read-only "/run/archiso/img_dev/${img_loop}"); then
+        archisodevice="${_dev_loop}"
+    else
         echo "ERROR: Setting loopback device for file '/run/archiso/img_dev/${img_loop}'"
         launch_interactive_shell
     fi
diff --git a/docs/README.altbootmethods b/docs/README.altbootmethods
index 3c07e03..cbfada4 100644
--- a/docs/README.altbootmethods
+++ b/docs/README.altbootmethods
@@ -25,20 +25,23 @@ Where:
 
 Note: Described method is for using with GRUB2.
       GRUB2 is installed on target media and archlinux-<YYYY>.<MM>.<DD>-dual.iso
-      is at path <TARGET-PATH> on disk <D> and partition <P>,
-      where filesystem is labeled as <TARGET-FS-LABEL>.
+      is at path <TARGET-PATH> on disk <D> and partition <P>.
 
 menuentry "Arch Linux (x86_64)" {
+    set isopartition=hd<D>,<P>
     set isofile="/<TARGET-PATH>/archlinux-<YYYY>.<MM>.<DD>-dual.iso"
-    loopback loop (hd<D>,<P>)$isofile
-    linux (loop)/arch/boot/x86_64/vmlinuz archisolabel=<FS-LABEL> img_label=<TARGET-FS-LABEL> img_loop=$isofile
+    loopback loop ($isopartition)$isofile
+    probe -u $isopartition --set=isouuid
+    linux (loop)/arch/boot/x86_64/vmlinuz img_dev=/dev/disk/by-uuid/$isouuid img_loop=$isofile
     initrd (loop)/arch/boot/x86_64/archiso.img
 }
 
 menuentry "Arch Linux (i686)" {
+    set isopartition=hd<D>,<P>
     set isofile="/<TARGET-PATH>/archlinux-<YYYY>.<MM>.<DD>-dual.iso"
-    loopback loop (hd<D>,<P>)$isofile
-    linux (loop)/arch/boot/i686/vmlinuz archisolabel=<FS-LABEL> img_label=<TARGET-FS-LABEL> img_loop=$isofile
+    loopback loop ($isopartition)$isofile
+    probe -u $isopartition --set=isouuid
+    linux (loop)/arch/boot/i686/vmlinuz img_dev=/dev/disk/by-uuid/$isouuid img_loop=$isofile
     initrd (loop)/arch/boot/i686/archiso.img
 }
 





One more thing - I would vote for deprecating "img_label" parameter and (sooner or later) removing it, i.e.

/archiso/initcpio/hooks/archiso_loop_mnt
-    [[ -n "${img_label}" ]] && img_dev="/dev/disk/by-label/${img_label}"

/docs/README.bootparams
-* img_label=        Set the filesystem label where archiso-image.iso.
-                    Default: (unset)
 * img_dev=          Device where archiso-image.iso reside.
-                    Default: (unset) or "/dev/disk/by-label/${img_label}"
+                    Default: (unset)

since: 1) it is more reliable to refer to a partition by uuid
2) there is no "img_uuid" - and I don't think there should be, "img_dev=/dev/disk/by-uuid/[uuid]" is perfectly fine
3) it would be still possible to address by label using "img_dev=/dev/disk/by-label/[label]"

Not sure how much upheaval the abolition of img_label would cause, though.