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Date: Tue, 01 Feb 2011 16:02:42 +0100
From: Jes Sorensen <Jes.Sorensen@redhat.com>
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Subject: [Qemu-devel] Re: [PATCH 1/2] Add virtagent file system freeze/thaw
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To: Adam Litke <agl@us.ibm.com>
Cc: qemu-devel@nongnu.org, mdroth@linux.vnet.ibm.com

On 02/01/11 15:48, Adam Litke wrote:
> On Tue, 2011-02-01 at 11:58 +0100, Jes.Sorensen@redhat.com wrote:
>> +/*
>> + * va_fsfreeze(): Walk list of mounted file systems in the guest, and
>> + *   freeze the ones which are real local file systems.
>> + * rpc return values: Number of file systems frozen, -1 on error.
>> + */
>> +static xmlrpc_value *va_fsfreeze(xmlrpc_env *env,
>> +                                 xmlrpc_value *params,
>> +                                 void *user_data)
>> +{
>> +    xmlrpc_int32 ret = 0, i = 0;
>> +    xmlrpc_value *result;
>> +    struct direntry *entry;
>> +    int fd;
>> +    SLOG("va_fsfreeze()");
>> +
>> +    if (fsfreeze_status == FREEZE_FROZEN) {
>> +        ret = 0;
>> +        goto out;
>> +    }
>> +
>> +    ret = build_mount_list();
>> +    if (ret < 0) {
>> +        goto out;
>> +    }
>> +
>> +    fsfreeze_status = FREEZE_INPROGRESS;
>> +
>> +    entry = mount_list;
>> +    while(entry) {
>> +        fd = qemu_open(entry->dirname, O_RDONLY);
>> +        if (fd == -1) {
>> +            ret = errno;
>> +            goto error;
>> +        }
>> +        ret = ioctl(fd, FIFREEZE);
>> +        if (ret < 0 && ret != EOPNOTSUPP) {
>> +            goto error;
>> +        }
> 
> Here we silently ignore filesystems that do not support the FIFREEZE
> ioctl.  Do we need to have a more complex return value so that we can
> communicate which mount points could not be frozen?  Otherwise, an
> unsuspecting host could retrieve a corrupted snapshot of that
> filesystem, right?

That is correct, however most Linux file systems do support it, and for
the ones that don't, there really isn't anything we can do.

Cheers,
Jes