Re: [Qemu-devel] [PATCH v5.1 2/2] qga-win: add driver path usage to GuestFilesystemInfo

[Chen Hanxiao]

At 2018-06-02 01:15:14, "Eric Blake" <address@hidden> wrote:
>On 06/01/2018 11:57 AM, Chen Hanxiao wrote:
>> From: Chen Hanxiao <address@hidden>
...
>>           fs->mountpoint = g_strdup("System Reserved");
>>       } else {
>>           fs->mountpoint = g_strndup(mnt_point, len);
>> +        if (GetDiskFreeSpaceEx(fs->mountpoint,
>> +                               (PULARGE_INTEGER) & i64FreeBytesToCaller,
>> +                               (PULARGE_INTEGER) & i64TotalBytes,
>> +                               (PULARGE_INTEGER) & i64FreeBytes)) {
>> +            fs->used_bytes = i64TotalBytes - i64FreeBytes;
>> +            fs->total_bytes = i64TotalBytes;
>> +            fs->has_total_bytes = true;
>> +            fs->has_used_bytes = true;
>> +        }
>
>I'm less familiar with Windows API, so I won't give this R-b. But now 
>that I read this patch, I do have a question: since both statvfs() and 
>GetDiskFreeSpaceEx() give you free bytes rather than used bytes, and you 
>had to perform a subtraction to report 'used-bytes' over QGA, would it 
>make any more sense to instead report 'free-bytes' over QGA for less 
>subtraction work on your end and so that the QGA interface is more 
>similar to existing interfaces?
>


All build-in tools report used-bytes for linux and windows.

For windows, GetDiskFreeSpaceEx would tell total and free bytes,
used bytes is  total - free,  which is exactly same
from the view of disk properties.

But for linux, df(1) do some calculation for showing used-bytes and free-bytes.

df(1) takes f_blocks - f_bfree for 'Used' ,
which take 'Used' + 'Available'(f_bavail)  for non-root total, 
which is different from 'Size'(f_blocks);
Then calculate  'Use%' by Used / non-root-total.

If we want get what df(3) outputs, we must report more members of struct 
statvfs  from STATVFS(3) ,
which windows does not need it.
And client had to do some calculation with if-else dealing with data from 
windows/linux.

Customs usually take 'Use%' to monitor their disks,
so I think we should report nums that can easily get the right percentage of 
usage from it,
for both linux and windows.

Regards,
- Chen