Libguestfs - Apr 2023 - Using nested partition with LUKS+GPT

Hi

I have already fulfill a an issue, but it looks like it's not the 
recommended process.

We are using a LUKS partition containing a GPT table and several partions.

With libguestfs we can open the LUKS partition and the 
|/dev/mapper/<mapname>| device become available, but nested partition 
are not seen by the kernel. |partprobe| need to be run (or may be 
kpartx) to make partitions available in |/dev/mapper|.

AFAIK there are no simple solution.
As a workaround we use |guestfs_debug| but it's not a long term solution.

We can see two solutions:

  * adding a udev rule that will automatically run partpobe when a new
    device appeared in /dev/mapper
  * adding a new API in libguestfs |guestfs_partprobe(device)| that can
    be call by the user when needed.

What is the best best solution from your point of view?
We can help implementing it.

Regards

Philippe Midol-Monnet


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On Fri, Apr 28, 2023 at 03:32:57PM +0200, Philippe Midol-Monnet
wrote:
> Hi
> 
> I have already fulfill a an issue, but it looks like it's not the
recommended
> process.
> 
> 
> We are using a LUKS partition containing a GPT table and several partions.
> 
> With libguestfs we can open the LUKS partition and the
/dev/mapper/<mapname>
> device become available, but nested partition are not seen by the kernel.
> partprobe need to be run (or may be kpartx) to make partitions available in
/
> dev/mapper.
> 
> AFAIK there are no simple solution.
> As a workaround we use guestfs_debug but it's not a long term solution.
> 
> We can see two solutions:
> 
>   ? adding a udev rule that will automatically run partpobe when a new
device
>     appeared in /dev/mapper
>   ? adding a new API in libguestfs guestfs_partprobe(device) that can be
call
>     by the user when needed.
> 
> What is the best best solution from your point of view?
> We can help implementing it.
I don't think there's any great answers here.  Could you do the
partition selection outside libguestfs?  If it was a plain (not LUKS)
partition then the answer would be yes, easily, with
nbdkit-partition-filter:

https://libguestfs.org/nbdkit.1.html#Combining-plugins-and-filters

nbdkit also supports LUKS, but only LUKS v1, not the more common v2.

Rich.

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