[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH 1/2] qemu-ga: execute script to quiesce the gues
From: |
Tomoki Sekiyama |
Subject: |
Re: [Qemu-devel] [PATCH 1/2] qemu-ga: execute script to quiesce the guest on fsfreeze-freeze/thaw |
Date: |
Mon, 12 Nov 2012 13:10:17 +0900 |
User-agent: |
Mozilla/5.0 (Windows NT 5.1; rv:16.0) Gecko/20121005 Thunderbird/16.0 |
Hi Eric, thanks for your review.
On 2012/11/09 3:38, Eric Blake wrote:
> On 11/08/2012 05:05 AM, Tomoki Sekiyama wrote:
>
> [Recoding to UTF-8, as ISO-2022-JP is not universally installed these
> days - you may want to reconsider your mailer's defaults]
Now this should be UTF-8, sorry.
>> To use the online disk snapshot for online-backup, application-level
>> consistency of the snapshot image is required. However, currently the
>> guest agent can provide only filesystem-level consistency, and the
>> snapshot may contain dirty data, for example, incomplete transactions.
>> This patch provides the opportunity to quiesce applications before
>> snapshot is taken.
>>
>> When the qemu-ga receives fsfreeze-freeze command, the script specified
>> in --fsfreeze-script option is executed with "freeze" argument before the
>> filesystem is frozen. For fsfreeze-thaw command, the script is executed
>> with "thaw" argument after the filesystem is thawed.
>>
>> Signed-off-by: Tomoki Sekiyama <address@hidden>
>> ---
>
>> @@ -396,6 +397,34 @@ GuestFsfreezeStatus qmp_guest_fsfreeze_status(Error
>> **err)
>> return GUEST_FSFREEZE_STATUS_THAWED;
>> }
>>
>> +int execute_fsfreeze_script(const char *arg)
>> +{
>> + int ret = -1;
>> + const char *fsfreeze_script;
>> + char *cmdline;
>> + struct stat st;
>> +
>> + fsfreeze_script = ga_fsfreeze_script(ga_state);
>> + if (fsfreeze_script && stat(fsfreeze_script, &st) == 0) {
>> + if (S_ISREG(st.st_mode) && (st.st_mode & S_IXUSR)) {
>
> Is it any simpler to use access(fsfreeze_script, X_OK) to check if the
> script exists and is executable?
OK, I will use access() here.
<snip>
>> + ret = system(cmdline);
>
> ...system() is not required to be thread-safe, but we should assume that
> qemu-ga is multi-threaded, and therefore we should not use system.
> Besides executing things via an extra layer of shell opens doors for
> further problems; for example, if the user starts qemu-ga with
> --fsfreeze-script '/path/with spaces/script', your command line is
> horribly broken when passed through the shell. It would be much better
> to directly fork() and exec() the script ourselves instead of relying on
> system().
I will use fork()/exec() method instead of system(), as in shutdown,
so I can remove malloc/free.
>> + if (ret > 0) {
>> + g_warning("fsfreeze script failed with status=%d", ret);
>
> This is a potentially misleading message; you should be using macros
> such as WEXITSTATUS when interpreting the result of system(), since not
> all systems return exit status 1 in the same bit position.
OK. I will refine error messages.
> The idea of having the freeze and thaw actions hook out to
> user-specified actions for additional steps seems nice, but this patch
> series needs a lot more work.
Regards,
--
Tomoki Sekiyama <address@hidden>
Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory