[Libguestfs] [libguestfs PATCH] guestfs.pod: document encrypted RBD disk limitation

[Laszlo Ersek]

On 05/18/22 11:30, Richard W.M. Jones wrote:
> On Wed, May 18, 2022 at 10:30:14AM +0200, Laszlo Ersek wrote:
>> Under "REMOTE STORAGE", the "NETWORK BLOCK DEVICE" section already
>> documents some limitations. Turns out we need to describe a quirky
>> exception for accessing encrypted RBD disks, too.
>>
>> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2033247
>> Signed-off-by: Laszlo Ersek <lersek at redhat.com>
>> ---
>>  lib/guestfs.pod | 33 ++++++++++++++++++++
>>  1 file changed, 33 insertions(+)
>>
>> diff --git a/lib/guestfs.pod b/lib/guestfs.pod
>> index b04c28d62750..1ad44e7c2878 100644
>> --- a/lib/guestfs.pod
>> +++ b/lib/guestfs.pod
>> @@ -679,6 +679,39 @@ servers.  The server string is documented in
>>  L</guestfs_add_drive_opts>. The C<username> and C<secret> parameters are
>>  also optional, and if not given, then no authentication will be used.
>>  
>> +An encrypted RBD disk -- I<directly> opening which would require the
>> +C<username> and C<secret> parameters -- cannot be accessed if the
>> +following conditions all hold:
>> +
>> +=over 4
>> +
>> +=item *
>> +
>> +the L<backend|/BACKEND> is libvirt,
>> +
>> +=item *
>> +
>> +the image specified by the C<filename> parameter is different from the
>> +encrypted RBD disk,
>> +
>> +=item *
>> +
>> +the image specified by the C<filename> parameter has L<qcow2
>> +format|/COMMON VIRTUAL DISK IMAGE FORMATS>,
>> +
>> +=item *
>> +
>> +the encrypted RBD disk is specified as a backing file at some level in
>> +the qcow2 backing chain.
>> +
>> +=back
>> +
>> +This limitation is due to libvirt's (justified) separate handling of
>> +disks vs. secrets.  When the RBD username and secret are provided inside
>> +a qcow2 backing file specification, libvirt does not construct an
>> +ephemeral secret object from those, for Ceph authentication.  Refer to
>> +L<https://bugzilla.redhat.com/2033247>.
>> +
>>  =head3 FTP, HTTP AND TFTP
> 
> Seems fine.  I had to look at perlpod(1) to check that the piped L<>
> references were correct, but they seem to be!
> 
> Acked-by: Richard W.M. Jones <rjones at redhat.com>
> 
> Rich.
> 

Commit 544bb0ff5079 ("guestfs.pod: document encrypted RBD disk
limitation", 2022-05-19).

Thanks
Laszlo