[libvirt] [PATCH] virsh: Use old API if remote libvirtd does not support new

[Eric Blake]

On 09/13/2011 09:16 AM, Peter Krempa wrote:
> Commit ffe28ab74b821c916ec4ba8efb5c992454e4bd24 introduced regression
> while comunicating with older libvirtd command 'domblkstat' used the new
> API and did not check for VIR_ERR_RPC error code signalling the remote
> server does not support this API and did not fall back to older API.
> Thereafter 'domblkstat' ended with "error: unknown procedure: 243".
> ---

ACK.

> footnote: Will not apply along with:
> [libvirt] [PATCH v5] virsh: Add more human-friendly output of domblkstat command
> as that path does fix this bug.

Apply this first, then rebase that patch into a v6.  Then the 
human-friendly patch is separate, rather than pushing two fixes in one 
patch (that is, upstream should have two patches, while for back-porting 
purposes, it might make sense to backport just this).

>
>   tools/virsh.c |    3 ++-
>   1 files changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/tools/virsh.c b/tools/virsh.c
> index 3b060bf..430168c 100644
> --- a/tools/virsh.c
> +++ b/tools/virsh.c
> @@ -1090,7 +1090,8 @@ cmdDomblkstat (vshControl *ctl, const vshCmd *cmd)
>        * then.
>        */
>       if (rc<  0) {
> -        if (last_error->code != VIR_ERR_NO_SUPPORT) {
> +        if (last_error->code != VIR_ERR_NO_SUPPORT&&
> +            last_error->code != VIR_ERR_RPC) {

Hmm, I wonder if any of my recent snapshot patches also need to check 
for VIR_ERR_RPC (for example, see cmdUndefine, which checks for 
VIR_ERR_NO_SUPPORT but not VIR_ERR_RPC).  Yep, I'm starting to convince 
myself that they do - if you have a new client talking to a pre-0.8.0 
server, then virDomainSnapshotNum would fail with VIR_ERR_RPC rather 
than VIR_ERR_NO_SUPPORT.

Or, maybe this means that we have a bug in our RPC code - when the local 
side gets VIR_ERR_RPC from the remote side due to unknown rpc number, 
should the local side be translating that into VIR_ERR_NO_SUPPORT 
instead of passing it back to the user as VIR_ERR_RPC?  But only for 
unknown rpc numbers; for other rpc errors, VIR_ERR_RPC still makes sense.

-- 
Eric Blake   eblake at redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org