In POST:
https://www.redhat.com/archives/libvir-list/2011-September/msg00547.html

There is no need to adjust the server side - the bug is only present when talking older server to newer client.  Since an older client talking to a newer server should never be sending unknown RPC in the first place, it will never trigger the error message, so the newer server does not have to bend over backwards to preserve the older-style errors.  That is, 0.9.4 is the only release where this problem hits, and only when talking to an 0.9.3 server with one of the APIs added in 0.9.4.  Therefore, the fix is only on the client side.

Since this is a client side fix, the only way to test that RHEL has the fix is to use a server running 0.9.3 and a fixed RHEL 0.9.4 client that triggers one of the APIs present only in 0.9.4.

Test this bug :

Server: 
libvirt-0.9.3-2.el6.x86_64 

Client: 
libvirt-0.9.4-12.el6.x86_64


In client : 
virsh -c qemu+ssh://10.66.85.207/system 

virsh # domblkstat t hda

domblkstat t hda
hda rd_req 42882
hda rd_bytes 130320896
hda wr_req 196
hda wr_bytes 1790976
hda errs 0


virsh # save-image-edit help
error: unknown procedure: 235

hi , Eric Blake 

I try to verify this bug with  Comment 5  , but I am not sure whether my way is orrect , so  please help me confirm it ,thanks . 
If my way is wrong ,please tell me the correct verify method  thanks very much .

Wenlong

In virsh, save-image-edit doesn't make any decisions based on the error given for a failed rpc function, and it has a custom error handler that does not display full error information to the user.  So I think we have to write a simple program (C or python) rather than relying on virsh, to properly verify this.  This program should do the trick when compiled against 0.9.4 (or newer), and targetting a server of 0.9.3:

$ cat foo.c
#include <stdio.h>
#include <libvirt/libvirt.h>
#include <libvirt/virterror.h>
int main(int argc, char **argv) {
    if (argc < 3) {
        fprintf(stderr, "usage: %s uri file\n", argv[0]);
        return 1;
    }
    virConnectPtr conn = virConnectOpenAuth(argv[1], virConnectAuthPtrDefault,
                                            0);
    if (!conn) {
        fprintf(stderr, "unable to open connection to %s\n", argv[1]);
        return 1;
    }
    char *xml = virDomainSaveImageGetXMLDesc(conn, argv[2], 0);
    if (xml) {
        fprintf(stderr, "server is too new\n");
        return 1;
    }
    virErrorPtr err = virGetLastError();
    if (!err) {
        fprintf(stderr, "missing error\n");
        return 1;
    }
    if (err->code != VIR_ERR_NO_SUPPORT) {
        fprintf(stderr, "wrong error code %d\n", err->code);
        return 1;
    }
    puts("success");
    virConnectClose(conn);
    return 0;
}
$ gcc -o foo foo.c -lvirt
$ ./foo qemu+ssh://remote/system /path/to/save/file
libvirt: RPC error : unknown procedure: 235
success

Note the expected error message mentions "RPC error", rather than "Remote error"

Verify  this bug in libvirt-0.9.4-12.el6.x86_64 :

Server: 
libvirt-0.9.3-2.el6.x86_64 

Client: 
libvirt-0.9.4-12.el6.x86_64



# cat foo.c
#include <stdio.h>
#include <libvirt/libvirt.h>
#include <libvirt/virterror.h>
int main(int argc, char **argv) {
    if (argc < 3) {
        fprintf(stderr, "usage: %s uri file\n", argv[0]);
        return 1;
    }
    virConnectPtr conn = virConnectOpenAuth(argv[1], virConnectAuthPtrDefault,
                                            0);
    if (!conn) {
        fprintf(stderr, "unable to open connection to %s\n", argv[1]);
        return 1;
    }
    char *xml = virDomainSaveImageGetXMLDesc(conn, argv[2], 0);
    if (xml) {
        fprintf(stderr, "server is too new\n");
        return 1;
    }
    virErrorPtr err = virGetLastError();
    if (!err) {
        fprintf(stderr, "missing error\n");
        return 1;
    }
    if (err->code != VIR_ERR_NO_SUPPORT) {
        fprintf(stderr, "wrong error code %d\n", err->code);
        return 1;
    }
    puts("success");
    virConnectClose(conn);
    return 0;
}

# ./foo qemu+ssh://10.66.85.207/system /tmp/foo.log
The authenticity of host '10.66.85.207 (10.66.85.207)' can't be established.
RSA key fingerprint is c9:4d:b4:d9:cf:bd:ca:56:72:4b:42:7d:86:38:7b:fd.
Are you sure you want to continue connecting (yes/no)? yes
root.85.207's password: 
libvir: RPC error : unknown procedure: 235
success

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHBA-2011-1513.html