Re: [PATCH V4 4/4] kdumpctl: force rebuild in case of file system UUID changes

[Xunlei Pang]

On 2016/04/27 at 17:23, Pratyush Anand wrote:
> Hi Xunlei,
>
> Thanks for the review.
>
> On Wed, Apr 27, 2016 at 2:28 PM, Xunlei Pang  wrote:
> > On 2016/04/20 at 18:07, Pratyush Anand wrote:
> > > kdump also passes persistent device mapping as --mount or --device argument
> > > of dracut. However this persistent id (UUID) is changed if dump target is
> > > re-formated.
> > > kdumpctl must have a mechanism to recognise this modification, so that its
> > > service restart is able to rebuild initramfs.
> > >
> > > Testing:
> > > a) Attach an IDE device, lets say it is /dev/sdb1
> > > b) Format it as ext4
> > >       # mkfs.ext4 /dev/sdb1
> > >       # blkid /dev/sdb1
> > >       /dev/sdb1: UUID="21c7baff-e35d-49c7-aa08-0fba4513f5bf" TYPE="ext4"
> > > c) Mount it into /mnt and create a var/crash directory in it.
> > >       # mount /dev/sdb1 /mnt;mkdir /mnt/var;mkdir /mnt/var/crash
> > > d) Add following line in /etc/kdump.conf
> > >       ext4 /dev/sdb1
> > > e) Restart kdumpctl
> > >       # kdumpctl restart
> > > f) crash
> > >       # echo c > /proc/sysrq-trigger
> > > g) Here you will be able save vmcore with or without this patch.
> > > h) repeat step (b), (c), (e) and (f)
> > > i) Now you will be able to save vmcore only when you have this patch in
> > > your kexec-tools. Your initramfs will be rebuilt when you repeat step (e)
> > > after reformatting.
> > > Signed-off-by: Pratyush Anand
> > >
> > > kdumpctl | 39 +++++++++++++++++++++++++++++++++++++++
> > >  1 file changed, 39 insertions(+)
> > >
> > > diff --git a/kdumpctl b/kdumpctl
> > > index 1cba00b9dc0f..f7e3af8733f5 100755
> > > --- a/kdumpctl
> > > +++ b/kdumpctl
> > > @@ -359,6 +359,39 @@ is_files_modified()
> > >       return 0
> > >  }
> > >
> > > +is_fs_uuid_changed()
> > > +{
> > > local _target _dracut_args _uuid
> > > _target=$(egrep "^ext[234]|^xfs|^btrfs" /etc/kdump.conf)
> > > #if dump target does not exist then do not rebuild
> > > [[ -n "$_target" ]] || return 0
> > > _dracut_args=$(lsinitrd $TARGET_INITRD | grep "^Arguments:" | head -1)
> > > if [[ -z "$_dracut_args" ]];then
> > >         echo "Warning: No dracut arguments found in initrd"
> > >         return 0
> > > fi
> > > #if --mount or --device is not by UUID, then also do not rebuild
> > > echo $_dracut_args | grep "by-uuid" &> /dev/null
> > > [[ $? -eq 0 ]] || return 0
> >
> > May be "[[ $? -ne 0 ]] && return 0" is more readable, but that's ok :-)
>
> OK..Will use above format from next time.
> > Additionally, for device mappers, if they got reformatted, because the persistent name
> > is from "/dev/mapper" not from "/dev/disk/by-uuid", will "return 0" here, not rebuilt.
> > Should we handle this?
>
> we do not need to rebuild in that case. Persistent name would be valid
> and so dracut will create valid root mount point.

Yes, but if a device mapper device is reformatted to be a different filesystem,
its uuid is changed(after remount, its fstype changes), then user restart kdump,
shouldn't we trigger rebuilding to update its mount fstype passed to dracut?

Regards,
Xunlei
> ~Pratyush