Re: LVM support

[ludo@gnu.org (Ludovic Courtès)]

Sorry for the delay.

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?


[...]

>>>           (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!).

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

Thanks,
Ludo’.