On 06/24/2014 06:50 AM, Puneet Bakshi wrote:
> Hi,
>
>>From host, I wrote 26 alphabets in guest file (/tmp/testqga) using
> guest-file-write guest agent command (logs pasted below). I faced 2 issues
> when doing that.
>
> 1a. It could wrote only 18bytes! Why could it not write all 26 characters?
> Are we supposed to track how much data is written and need to resend the
> remaining one?
You aren't using the command correctly. The qemu-guest-agent interface
for guest-file-write expects data to be base64-encoded.
>
> 1b. What is the limit of data, I can send in one guest-file-write command?
That's a question for the qemu list, as qemu-guest-agent is maintained
there, not here.
>
> 2. In the guest, file data seems to be different. Am I doing something
> wrong here?
Yes, you aren't encoding your data properly.
>
>
> Host (file write)
>
> [root@sdsr720-14 ~]# virsh qemu-agent-command vm_04 '{"
> execute":"guest-file-open", "arguments":{"path":"/tmp/testqga","mode":"w
> +"}}'
Remember, the use of qemu-agent-command is EXPLICITLY unsupported by
libvirt. It's there as a debugging and development aid, and NOT
something you should be using in your production environment.
I *highly* recommend that you figure out how to set up shared file
systems (NFS, gluster, plan9, MTP, ...) so that you can have the guest
read a file already exported by the host through existing shared
filesystem code, rather than slogging through trying to write the file
through arcane invocations of the qemu-guest-agent.
>
> [root@sdsr720-14 ~]# virsh qemu-agent-command vm_04 '{"
> execute":"guest-file-write",
> "arguments":{"handle":1000,"buf-b64":"abcdefghijklmnopqrstuvwxyz"}}'
>
> {"return":{"count":18,"eof":false}}
That is NOT a valid base64 encoded buffer.
$ printf abcdefghijklmnopqrstuvwxyz | base64 -d | od -tx1z
base64: invalid input
0000000 69 b7 1d 79 f8 21 8a 39 25 9a 7a 29 aa bb 2d ba >i..y.!.9%.z)..-.<
0000020 fc 31 cb >.1.<
0000023
>
> [root@vm04 qga]# cat /tmp/testqga
>
> i�^]y�!�9%�z)��-��1[root@vm04 qga]#
But those contents match the base64 decoding of (the valid portion of)
the buffer that you passed in. So the only bug here is in your usage,
not in qemu-guest-agent or in libvirt.
-
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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