Re: [PATCH] Introduce dom0-min-space configuration option

[Michal Novotny <minovotn@redhat.com>]

On 07/26/2010 01:31 PM, Paolo Bonzini wrote:
> On 07/26/2010 01:21 PM, Michal Novotny wrote:
>> On 07/26/2010 01:18 PM, Paolo Bonzini wrote:
>>> On 07/26/2010 12:36 PM, Michal Novotny wrote:
>>>> On 07/26/2010 11:59 AM, Paolo Bonzini wrote:
>>>>> On 07/26/2010 08:55 AM, Michal Novotny wrote:
>>>>>> Or do you think that we should alter the message in gunzip 
>>>>>> function to
>>>>>> say that there's an error in data stream (premature end of data
>>>>>> stream)
>>>>>> and that user should check for enough space on dom0?
>>>>>
>>>>> No, the gunzip function (in libxc, if I understood the context) 
>>>>> should
>>>>> not even be called if pygrub could not write the file. Instead, it
>>>>> should print something like
>>>>>
>>>>> pygrub: No space left on device
>>>>>
>>>>> and exit. There's absolutely no error checking here:
>>>>>
>>>>> data = fs.open_file(chosencfg["kernel"]).read()
>>>>> (tfd, bootcfg["kernel"]) = tempfile.mkstemp(prefix="boot_kernel.",
>>>>> dir="/var/run/xend/boot")
>>>>> os.write(tfd, data)
>>>>> os.close(tfd)
>>>>>
>>>>> (and likewise for initrd) and that's the bug.
>>>>>
>>>>> Paolo
>>>>
>>>> Paolo, that's correct but the issue here is that we don't know 
>>>> until we
>>>> extract it from image file.
>>>
>>> os.write would return -1 and set errno to ENOSPC (besides, any other
>>> errno should get the same treatment), no?
>>
>> Maybe, I need to check the docs first but you're most likely right about
>> this. Nevertheless this is the pygrub code AFAIK so some patch for xend
>> would be necessary as well, otherwise libvirt-based tools would complain
>> with "Boot loader didn't return any data!" message.
>
> That's the least of the problems, if a sensible error message is 
> present too.  I agree with Ian, let's first fix the main cause.  Then 
> we can see what the fallout is.
>
> Paolo
Well, the root cause is insufficient disk space since without 
insufficient disk space issue we won't be running into those issues. In 
fact there are 2 points of view on this one:

  1) implement a check for enough disk space (this is what I did)
  2) implement the proper error message saying there is not enough space 
to extract it (ENOSPC) - this is what you and Ian suggest

I am not telling any of those options is bad, nevertheless it's based 
just on the point of view. So, is option 2 better  and worth 
implementing rather than limiting the domain run only to case with 
enough space on dom0?

Michal


-- 
Michal Novotny<minovotn@redhat.com>, RHCE
Virtualization Team (xen userspace), Red Hat