[syslinux] [PATCH] : Adding dlabel option to chain.c32

[Erwan Velu]

The idea is to boot a disk in an mbr fashion while using the GPT (not
filesystem) label to detect the disk.

That is useful when you use grub2 & gpt. I was in case where my nodes
(100s) have 8 disks each and no guarantee of which disk is "bootable" in
the disk.

This way I can tell "please boot the disk that have one partition labelled
"xyz"".

So nothing related to filesystem but gpt labels & disks.

2016-07-15 18:27 GMT+02:00 poma <pomidorabelisima at gmail.com>:

> On 15.07.2016 17:53, Ady Ady via Syslinux wrote:
> >
> >> On 30.06.2016 19:41, Erwan Velu via Syslinux wrote:
> >>> The exisiting label= option offer to boot on a gpt partition that have
> >>> a particular label.
> >>> The existing guuid= option offer to boot on a disk or partition with a
> >>> particular label.
> >>>
> >>> This new option offer to boot the disk that have a partition which
> >>> have a given label.
> >>> The label is so just a way to detect a disk to boot.
> >>>
> >>> A typical use is for making an intelligent localboot like :
> >>>
> >>>     label localboot
> >>>         com32 chain.c32
> >>>         append dlabel=datapartition
> >>>
> >>> This allow booting on a disk that sports a least one partition
> >>> labelled "datapartition".
> >>>
> >>> You can consider dlabel= doing almost what mbr= does but by inspecting
> >>> the gpt partitions label.
> >>>
> >>>
> >>> Please find below the commit :
> >>>
> https://github.com/ErwanAliasr1/syslinux/commit/ebf8cbfb8cef49517aa36b4a79998b4332289489
> >>>
> >>
> >>
> >> # gdisk -l /dev/vda
> >> ...
> >> Partition table scan:
> >>   MBR: protective
> >>   BSD: not present
> >>   APM: not present
> >>   GPT: present
> >>
> >> Found valid GPT with protective MBR; using GPT.
> >> ...
> >> Number  Start (sector)    End (sector)  Size       Code  Name
> >>    1            2048          411647   200.0 MiB   EF00  EFI System
> Partition
> >>    2          411648         1435647   500.0 MiB   8300  BOOT System
> Partition
> >>    3         1435648        22646783   10.1 GiB    8300  ROOT System
> Partition
> >>    4        22646784        25163775   1.2 GiB     8200  SWAP System
> Partition
> >>
> >>
> >> # fdisk -l /dev/vda
> >> ...
> >> Disklabel type: gpt
> >> ...
> >> Device        Start      End  Sectors  Size Type
> >> /dev/vda1      2048   411647   409600  200M EFI System
> >> /dev/vda2    411648  1435647  1024000  500M Linux filesystem
> >> /dev/vda3   1435648 22646783 21211136 10.1G Linux filesystem
> >> /dev/vda4  22646784 25163775  2516992  1.2G Linux swap
> >>
> >>
> >> # fatlabel /dev/vda1
> >> labelefi
> >>
> >> # e2label /dev/vda2
> >> labelboot
> >>
> >> # e2label /dev/vda3
> >> labelroot
> >>
> >> # swaplabel /dev/vda4
> >> LABEL: labelswap
> >> ...
> >>
> >>
> >> Filesystem *label* and *label* of a swap area
> >> distinguish from
> >> GPT *name* of a partition
> >>
> >
> >
> > _If_ I understand Erwan's patch correctly, we are talking about the GPT
> Partition Name, not the
> > filesystem's label (but I could be wrong).
> >
> >
> >>
> >> Therefore -if- you are referring to a GPT partition *name*,
> >> simple *name* as append option - for GPT partition *name* selection,
> should suffice
> >> i.e.
> >>   ...
> >>   append name=gptpartitionname
> >
> >
> > Not exactly. We are distinguishing between the GPT Partition Name being
> used just to select the
> > next device (for example, your "ROOT System Partition"), and the
> (Protective) MBR we are jumping
> > to, in BIOS / CSM mode.
> >
> > In my prior email I suggested "diskbypartname" with relevant
> explanations (see
> > http://www.syslinux.org/archives/2016-July/025305.html ).
> >
> > Tests and feedback are appreciated.
> >
> > Regards,
> > Ady.
> >
>
> For once, precise explanation of the author is really required,
> afterwards the actual option name should not be a problem
>
> e.g.
> append icecream=whicheverflavor
> ;)
>
>
>