bug#35995: [wishlist] bootloader-configuration, avoid use of /dev/sd?

bug#35995: [wishlist] bootloader-configuration, avoid use of /dev/sd?

[Giovanni Biscuolo]

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Hello,

Following a recent discussion on Guix-devel [1] I'm "forwarding here" a
proposal to switch from /dev/sd? to (target (uuid ...)) in
bootloader-configuration operating-system declaration

This is a recap of current situation: the installer usually uses
/dev/sda as target for grub-install (and bootloader-cofiguration) but it
happened to me that on a machine /dev/sda was the USB media, not the
target HD

The fact is that it's not guaranteed that /dev/sd? always corresponds to
the same device

This is where we are with the discussion:

Ludovic Courtès <ludo@gnu.org> writes:

> Hello!
>
> Giovanni Biscuolo <g@xelera.eu> skribis:
>
>> But wait! There's the /dev/disk/by-id/ tree, I did not notice it until
>> now! :-)
>>
>> That's the solution:
>>
>>
>>   (bootloader
>>     (bootloader-configuration
>>       (bootloader grub-bootloader)
>>       (target "/dev/disk/by-id/scsi-3600508b1001c75a3bebb04b23d19e249")
>>       (keyboard-layout keyboard-layout)))
>>
>> I did not test this but it smells like running, if Guix devels agree I
>> think Installer should adopt /dev/disk/by-id by default, sorry I'm not
>> able to propose a patch for this
>
> Ideally, we’d use an actual UUID object (or a string?) here rather than
> this Linux/udev-specific idiom.  So it would look like:
>
>   (bootloader-configuration
>     ;; …
>     (target (uuid …)))
>
> Would that work?
>
> I believe using Guile-Parted we could map it back to a /dev name.
>
> WDYT?
>
> Ludo’.



[1] Message-ID: <87o93mwr4b.fsf@gnu.org>
    http://lists.gnu.org/archive/html/guix-devel/2019-05/msg00454.html

-- 
Giovanni Biscuolo

Xelera IT Infrastructures

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bug#35995: Installer: GUIX_IMAGE as /dev/sda on some hardware?

[Giovanni Biscuolo]

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Hello Tobias and Ludo'

I've opened a bug report for this, WDYT if we go on there?

Tobias Geerinckx-Rice <me@tobias.gr> writes:

> Ludovic Courtès wrote:
>> Ideally, we’d use an actual UUID object (or a string?) here 
>> rather than
>> this Linux/udev-specific idiom.  […]
>> I believe using Guile-Parted we could map it back to a /dev 
>> name.
>
> Yah, 's one of the reasons that I haven't sent anything yet (the 
> main one being shame, of course; car/cdr for the win & all that).
>
>> Would that work?
>
> I'd looked in Guile-parted before but came up dry.  To be fair I 
> did little more than grep around for ‘uid’ and friends.  So you 
> tell me ;-)
>
> …
>
> Hum, wait a minute.  Isn't that irrelevant?  Doesn't Guix itself 
> do exactly this when mounting file systems?  Sigh, silly me, I 
> should be able to re-use that…  >_<

Grub supports quite a number of ways to specify devices [1] but I cannot
find something suitable for this purpose: am I missimg something
obvious?

AFAIU on ther distros (e.g. Debian) (the installer?) populates a device
map [2] using the grub-mkdevicemap utility (grub-common package in
Debian) but I cannot find that in our grub package

This is an example on one of my Debian hosts:

--8<---------------cut here---------------start------------->8---

$ cat /boot/grub/device.map
(hd0)	/dev/disk/by-id/ata-WDC_WD10EADS-00L5B1_WD-WCAU4D992691
(hd1)	/dev/disk/by-id/ata-ST3250620NS_9QE2L68Z
(hd2)	/dev/disk/by-id/ata-ST3250620NS_9QE2FSQD
(hd3)	/dev/disk/by-id/ata-ST3250620NS_9QE27YPJ
(hd4)	/dev/disk/by-id/ata-WDC_WD7500BPKT-00PK4T0_WD-WX11A4181554
(hd5)	/dev/disk/by-id/ata-WDC_WD7500BPKT-00PK4T0_WD-WXM1A61D0766

--8<---------------cut here---------------end--------------->8---

(the map is not updated)

We could use (hd?) in grub config - that's grub specific, not Linux/udev
specific - **but** we should find a way to automate the selection of the
device corresponding to our target (the one mounted as /mnt)

Thanks for working on this!!!

Happy hacking. Gio'.



[1] https://www.gnu.org/software/grub/manual/grub/html_node/Device-syntax.html


[2] https://www.gnu.org/software/grub/manual/grub/html_node/Device-map.html

-- 
Giovanni Biscuolo

Xelera IT Infrastructures

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bug#35995: Installer: GUIX_IMAGE as /dev/sda on some hardware?

[Danny Milosavljevic]

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Grub already can search by uuid or label (via "search --fsuuid" and
"search --label", respectively).  IF you specify an uuid or label
in your operating-system configuration it will use that.

The only part missing is: The Guix installer's config generator should
find out the uuids and print those instead of the /dev nodes.

If nothing else, we can just use blkid to find out which is which.

For example: blkid -d -s UUID -o value /dev/sda1

But T G-R is right, Guix already does what is required at other places.

Care has to be taken that parted also uses GUIDs for GPT partition TYPES
and also for partitions as such (not their contents).  Those are something
else.

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bug#35995: Installer: GUIX_IMAGE as /dev/sda on some hardware?

[Ludovic Courtès]

Hi Danny,

Danny Milosavljevic <dannym@scratchpost.org> skribis:

> Grub already can search by uuid or label (via "search --fsuuid" and
> "search --label", respectively).  IF you specify an uuid or label
> in your operating-system configuration it will use that.

These are concerned with file system UUIDs/labels, whereas this issue is
about disk IDs, AIUI.  Or am I missing something?

Ludo’.

bug#35995: Installer: GUIX_IMAGE as /dev/sda on some hardware?

[Tobias Geerinckx-Rice]

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Ludovic Courtès wrote:
> Danny Milosavljevic <dannym@scratchpost.org> skribis:
>> Grub already can search by uuid or label (via "search --fsuuid" 
>> and
>> "search --label", respectively).  IF you specify an uuid or 
>> label
>> in your operating-system configuration it will use that.
>
> These are concerned with file system UUIDs/labels, whereas this 
> issue is
> about disk IDs, AIUI.  Or am I missing something?

This.  Also, this only affects grub-install—not ‘grub 
run-time’—which runs under the Hurd/Linux/…, unless I, too, am 
missing something, and this entire thread collapses in a cacophony 
of confusion.

G'night,

T G-R

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bug#35995: Installer: GUIX_IMAGE as /dev/sda on some hardware?

[Danny Milosavljevic]

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Yeah, but disk ids are not uuids.

/dev/disk/by-id seems to be a good way to find those disk ids in order to pass
them to grub-install.  I doubt that this can be made OS-independent--even the
udev rules specify different variables for different devices, sometimes it's
bus id and serial number, sometimes it's name and serial number, sometimes it's
ieee1394_id, sometimes ID_WWN_WITH_EXTENSION.

Alternatively, grub also works from a boot-active partition--it nothing else
works, we can install grub to a partition (for example the root partition).

Then, migration would be difficult, though (if people had grub installed on
the MBR, that destroyed the previous loader that would have loaded from the
boot sector of the partition).

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bug#35995: [wishlist] bootloader-configuration, avoid use of /dev/sd?

[Giovanni Biscuolo]

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Hello,

I think this bug has been fixed in bug #51878:

Pushed as b90504cdb5ce3d1981c8d7bc8a9cc918b0d60af7 (26 Nov 2021).

Closing! :-)

-- 
Giovanni Biscuolo

Xelera IT Infrastructures

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