Re: [PULL v3 05/12] qga: add command guest-get-disks

[Michael Roth]

Quoting Eric Blake (2020-11-04 15:56:17)
> [Adding Markus in CC]
> 
> On 11/2/20 8:43 PM, Michael Roth wrote:
> > From: Tomá\u0161 Golembiovský <tgolembi@redhat.com>
> > 
> > Add API and stubs for new guest-get-disks command.
> > 
> > The command guest-get-fsinfo can be used to list information about disks
> > and partitions but it is limited only to mounted disks with filesystem.
> > This new command should allow listing information about disks of the VM
> > regardles whether they are mounted or not. This can be usefull for
> > management applications for mapping virtualized devices or pass-through
> > devices to device names in the guest OS.
> > 
> > Signed-off-by: Tomá\u0161 Golembiovský <tgolembi@redhat.com>
> > Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> > Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > Signed-off-by: Michael Roth <michael.roth@amd.com>
> > ---
> >  qga/commands-posix.c |  6 ++++++
> >  qga/commands-win32.c |  6 ++++++
> >  qga/qapi-schema.json | 31 +++++++++++++++++++++++++++++++
> >  3 files changed, 43 insertions(+)
> 
> I know my review is late, since the PR is already accepted, but some
> items that may be worth followup patches in the 5.2 cycle:
> 
> 
> > +++ b/qga/qapi-schema.json
> > @@ -865,6 +865,37 @@
> >             'bus': 'int', 'target': 'int', 'unit': 'int',
> >             '*serial': 'str', '*dev': 'str'} }
> >  
> > +##
> > +# @GuestDiskInfo:
> > +#
> > +# @name: device node (Linux) or device UNC (Windows)
> > +# @partition: whether this is a partition or disk
> > +# @dependents: list of dependent devices; e.g. for LVs of the LVM this will
> > +#              hold the list of PVs, for LUKS encrypted volume this will
> > +#              contain the disk where the volume is placed.     (Linux)
> 
> Odd spacing before the comment.
> 
> Should @dependents be guarded by 'if', or are we avoiding the use of
> 'if' in qga for now and only using it in qmp?

Marc-André's recent guest-ssh-{get,add,remove}-authorized-keys patches are
the first users for qga I think. The CONFIG_{LINUX,POSIX,W32} is
becoming pretty unwieldly so I've been planning on going back and using
schema conditionals and refactoring things a bit anyway so I'm ok with
adding it later as long as the documentation is accurate.

> 
> Is 'dependents' the right name?  A common English use of 'dependent' is
> when talking about a family: a parent's child is their dependent (that
> is, a dependent tends to be the smaller entity).  But here, you are
> using the term in the opposite direction: this storage device (such as a
> LUKS encrypted drive) is declaraing a LARGER entity (the containing
> block device) as its dependent.  Would 'dependencies' or 'depends-on' be
> more accurate?

Agreed, 'dependencies' is probably a better name. The 'slaves' term
used in /sys can be a bit confusing in this regard as well, but
captures the relationship a bit better than 'dependents' as least.

> 
> > +# @address: disk address information (only for non-virtual devices)
> > +# @alias: optional alias assigned to the disk, on Linux this is a name 
> > assigned
> > +#         by device mapper
> > +#
> > +# Since 5.2
> > +##
> > +{ 'struct': 'GuestDiskInfo',
> > +  'data': {'name': 'str', 'partition': 'bool', 'dependents': ['str'],
> > +           '*address': 'GuestDiskAddress', '*alias': 'str'} }
> 
> 'dependents' is not an optional member, but documented as '(Linux)'
> above; does that mean you always get "dependents":[] on the wire for
> Windows, rather than omitting the field?

Yes, which seems a bit misleading to management. This should be made
optional.

I'll send a patch to address these.

Thanks for the review!

-Mike

> 
> > +
> > +##
> > +# @guest-get-disks:
> > +#
> > +# Returns: The list of disks in the guest. For Windows these are only the
> > +#          physical disks. On Linux these are all root block devices of
> > +#          non-zero size including e.g. removable devices, loop devices,
> > +#          NBD, etc.
> > +#
> > +# Since: 5.2
> > +##
> > +{ 'command': 'guest-get-disks',
> > +  'returns': ['GuestDiskInfo'] }
> > +
> >  ##
> >  # @GuestFilesystemInfo:
> >  #
> > 
> 
> -- 
> Eric Blake, Principal Software Engineer
> Red Hat, Inc.           +1-919-301-3226
> Virtualization:  qemu.org | libvirt.org
> 
>