Re: LVM support

["Tomáš Čech" <sleep_walker@gnu.org>]

[-- Attachment #1: Type: text/plain, Size: 3881 bytes --]

On Sun, May 03, 2015 at 09:59:53PM +0200, Ludovic Courtès wrote:
>Sorry for the delay.

Sorry for all the delays :)

>
>Tomáš Čech <sleep_walker@gnu.org> skribis:
>
>> On Tue, Apr 21, 2015 at 05:52:33PM +0200, Ludovic Courtès wrote:
>
>[...]
>
>>>So I would declare
>>>
>>>  (mapped-device
>>>    (source "/dev/sda")
>>>    (target "volume_group_name-logical_volume_name")
>>>    (kind lvm-device-mapping))
>>>
>>>and that would give me
>>>/dev/mapper/volume_group_name-logical_volume_name, right?
>>
>> Volume group can be on multiple block devices. For now I rely on autodetect
>> abilities of LVM.
>>
>> So you would declare:
>>
>> (mapped-device
>>  (source "") ; irrelevant for LVM
>>  (target "volume_group_name")
>>  (type lvm-mapping))
>>
>> and that would give you
>> /dev/mapper/volume_group_name-some_volume
>> /dev/mapper/volume_group_name-other_volume
>> ...
>>
>> and more conveniently
>> /dev/volume_group_name/some_volume
>> /dev/volume_group_name/other_volume
>> ...
>
>OK.  So the ‘source’ is irrelevant because ‘vgscan’ magically creates
>the device nodes for volumes such that users don’t have to know what the
>underlying block devices are, right?

Yes.


>[...]
>
>>>>           (boot-system #:mounts '#$(map file-system->spec file-systems)
>>>>                        #:pre-mount (lambda ()
>>>> -                                    (and #$@device-mapping-commands))
>>>> +                                    (and #$@device-mapping-commands
>>>> +                                         ;; If we activated any volume group, we
>>>> +                                         ;; need to ensure that device nodes are
>>>> +                                         ;; created.  Add code here to call it
>>>> +                                         ;; once for all activations.
>>>> +                                         #$(when (lvm-mapping-used? mapped-devices)
>>>> +                                             #~(zero?
>>>> +                                                (system* (string-append
>>>> +                                                          #$lvm2/static
>>>> +                                                          "/sbin/lvm.static")
>>>> +                                                         "vgscan"
>>>> +                                                         "--mknodes")))))
>>>
>>>So ‘lvm vgchange --activate y’ does not create /dev nodes?
>>
>> Right.
>>
>>>Would it be possible to change the command returned by
>>>‘logical-volume-group-activate’ to somehow create the nodes?  That would
>>>be ideal.
>>
>> There are two actions needed to be taken:
>> 1] volume group activation
>> 2] creation of nodes
>>
>> This design choice does as many 1] as needed and 2] once in the end.
>>
>> I could do always 1] and 2] for every volume group, but I didn't find it nice,
>> since previous 2] calls are useless only slowing down the process. Do you
>> really think I should change it?
>
>No, you’re right, what you did makes a lot of sense (thanks for bearing
>with me!).

Good.

>Could you send an updated patch?  It sounds like we’re almost there,
>I guess.

Not there yet. Now I need to make some changes with mounting order to help
non-root filesystems on LVM volume.

Right now it seems it tries to:
1] mount all filesystems
2] run udev

But I need to make it:
1] mount /dev
2] run udev service (with the `udevadm settle' in the end)
3] mount the rest of filesystems

It seems that /sys and /proc is mounted already from initrd phase using
mount-essential-file-systems. Is there reason not to put /dev there as well?

I see none so I'll try to add /dev filesystem mounting there (and to
move-essential-file-systems) and remove it from %base-file-systems.

Best regards,

S_W

[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 181 bytes --]