Re: [PATCH v2] Add GRUB_DISABLE_UUID

[Daniel Kiper]

Adding Nicholas...

On Mon, Sep 30, 2019 at 04:59:12PM +0200, Javier Martinez Canillas wrote:
> From: Peter Jones <address@hidden>
>
> The grub-mkconfig and 10_linux scripts by default attempt to use a UUID to
> set the root kernel command line parameter and the $root GRUB environment
> variable.
>
> The former can be disabled by setting the GRUB_DISABLE_LINUX_UUID variable
> to "true", but there is currently no way to disable the latter.
>
> The generated grub config uses the search command with the --fs-uuid option
> to find the device that has to be set as $root, i.e:
>
>  search --no-floppy --fs-uuid --set=root ...
>
> This is usually more reliable but in some cases it may not be appropriate,
> so this patch introduces a new GRUB_DISABLE_UUID variable that can be used
> to disable searching for the $root device by filesystem UUID.
>
> When disabled, the $root device will be set to the value specified in the
> device.map as found by the grub-probe --target=compatibility_hint option.
>
> When setting GRUB_DISABLE_UUID=true, the GRUB_DISABLE_LINUX_UUID and
> GRUB_DISABLE_LINUX_PARTUUID variables will also be set to "true" unless
> these have been explicitly set to "false".
>
> That way, the GRUB_DISABLE_UUID variable can be used to force using the
> device names for both GRUB and Linux.
>
> Signed-off-by: Peter Jones <address@hidden>
> Signed-off-by: Javier Martinez Canillas <address@hidden>

In general "Reviewed-by: Daniel Kiper <address@hidden>" but I would
like to hear Nicholas opinions here too.

Daniel

> ---
>
> Changes since v1 (suggested by Daniel Kiper):
>
> - Explain better in the commit message why the GRUB_DISABLE_UUID variable
>   is needed and the difference with the existing GRUB_DISABLE_LINUX_UUID/
>   GRUB_DISABLE_LINUX_PARTUUID variables.
> - Remove logic that disabled setting the root cmdline param to either the
>   filesystem UUID or partition UUID and instead use the existing variables
>   to disable this.
>
>  docs/grub.texi            |  9 +++++++++
>  util/grub-mkconfig.in     | 10 ++++++++++
>  util/grub-mkconfig_lib.in |  4 ++--
>  3 files changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/docs/grub.texi b/docs/grub.texi
> index 5ac61c09d1b..2fe0e1b83bb 100644
> --- a/docs/grub.texi
> +++ b/docs/grub.texi
> @@ -1441,6 +1441,15 @@ enable the use of partition UUIDs, set this option to 
> @samp{false}.
>  If this option is set to @samp{true}, disable the generation of recovery
>  mode menu entries.
>
> +@item GRUB_DISABLE_UUID
> +Normally, @command{grub-mkconfig} will generate menu entries that use
> +universally-unique identifiers (UUIDs) to identify various filesystems to
> +search for files.  This is usually more reliable, but in some cases it may
> +not be appropriate.  To disable this use of UUIDs, set this option to
> +@samp{true}. Setting this option to @samp{true}, will also set the options
> +@samp{GRUB_DISABLE_LINUX_UUID} and @samp{GRUB_DISABLE_LINUX_PARTUUID} to
> +@samp{true}, unless they have been explicilty set to @samp{false}.
> +
>  @item GRUB_VIDEO_BACKEND
>  If graphical video support is required, either because the @samp{gfxterm}
>  graphical terminal is in use or because @samp{GRUB_GFXPAYLOAD_LINUX} is set,
> diff --git a/util/grub-mkconfig.in b/util/grub-mkconfig.in
> index a6ce375ed18..2537dbca2f9 100644
> --- a/util/grub-mkconfig.in
> +++ b/util/grub-mkconfig.in
> @@ -158,6 +158,15 @@ if test -f ${sysconfdir}/default/grub ; then
>    . ${sysconfdir}/default/grub
>  fi
>
> +if [ "x${GRUB_DISABLE_UUID}" = "xtrue" ]; then
> +  if [ "x${GRUB_DISABLE_LINUX_UUID}" != "xfalse" ]; then
> +    GRUB_DISABLE_LINUX_UUID="true"
> +  fi
> +  if [ "x${GRUB_DISABLE_LINUX_PARTUUID}" != "xfalse" ]; then
> +    GRUB_DISABLE_LINUX_PARTUUID="true"
> +  fi
> +fi
> +
>  # XXX: should this be deprecated at some point?
>  if [ "x${GRUB_TERMINAL}" != "x" ] ; then
>    GRUB_TERMINAL_INPUT="${GRUB_TERMINAL}"
> @@ -227,6 +236,7 @@ export GRUB_DEFAULT \
>    GRUB_DISABLE_LINUX_UUID \
>    GRUB_DISABLE_LINUX_PARTUUID \
>    GRUB_DISABLE_RECOVERY \
> +  GRUB_DISABLE_UUID \
>    GRUB_VIDEO_BACKEND \
>    GRUB_GFXMODE \
>    GRUB_BACKGROUND \
> diff --git a/util/grub-mkconfig_lib.in b/util/grub-mkconfig_lib.in
> index 0f801cab3e4..3e12b2c0e6a 100644
> --- a/util/grub-mkconfig_lib.in
> +++ b/util/grub-mkconfig_lib.in
> @@ -156,7 +156,7 @@ prepare_grub_to_access_device ()
>    if [ "x$fs_hint" != x ]; then
>      echo "set root='$fs_hint'"
>    fi
> -  if fs_uuid="`"${grub_probe}" --device $@ --target=fs_uuid 2> /dev/null`" ; 
> then
> +  if [ "x${GRUB_DISABLE_UUID}" != "xtrue" ] && fs_uuid="`"${grub_probe}" 
> --device $@ --target=fs_uuid 2> /dev/null`" ; then
>      hints="`"${grub_probe}" --device $@ --target=hints_string 2> /dev/null`" 
> || hints=
>      echo "if [ x\$feature_platform_search_hint = xy ]; then"
>      echo "  search --no-floppy --fs-uuid --set=root ${hints} ${fs_uuid}"
> @@ -173,7 +173,7 @@ grub_get_device_id ()
>    IFS='
>  '
>    device="$1"
> -  if fs_uuid="`"${grub_probe}" --device ${device} --target=fs_uuid 2> 
> /dev/null`" ; then
> +  if [ "x${GRUB_DISABLE_UUID}" != "xtrue" ] && fs_uuid="`"${grub_probe}" 
> --device ${device} --target=fs_uuid 2> /dev/null`" ; then
>      echo "$fs_uuid";
>    else
>      echo $device |sed 's, ,_,g'
> --
> 2.21.0