[libvirt] [PATCH] lxc: remove redundant check

[Alex Jia]

On 10/27/2011 05:26 PM, Daniel P. Berrange wrote:
> On Thu, Oct 27, 2011 at 04:33:50PM +0800, Alex Jia wrote:
>> On 10/27/2011 04:20 PM, Daniel P. Berrange wrote:
>>> On Thu, Oct 27, 2011 at 03:18:01PM +0800, ajia at redhat.com wrote:
>>>> From: Alex Jia<ajia at redhat.com>
>>>>
>>>> Detected by cppcheck, the previous function VIR_REALLOC_N(mounts, nmounts+1)
>>>> can make sure mounts is a none null value, so it is redundant to check if
>>>> mounts is null.
>>> VIR_REALLOC_N is only executed inside the loop. Although it is unlikely,
>>> in theory there can be zero iterations of the loop, in which case
>>> 'mounts' will be NULL at the point qsort is called.
>>>
>>>> * src/lxc/lxc_container.c: remove redundant check.
>>>>
>>>> Signed-off-by: Alex Jia<ajia at redhat.com>
>>>> ---
>>>>   src/lxc/lxc_container.c |    5 ++---
>>>>   1 files changed, 2 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
>>>> index 06ccf7e..f4879c3 100644
>>>> --- a/src/lxc/lxc_container.c
>>>> +++ b/src/lxc/lxc_container.c
>>>> @@ -879,9 +879,8 @@ static int lxcContainerUnmountOldFS(void)
>>>>       }
>>>>       endmntent(procmnt);
>>>>
>>>> -    if (mounts)
>>>> -        qsort(mounts, nmounts, sizeof(mounts[0]),
>>>> -              lxcContainerChildMountSort);
>>>> +    qsort(mounts, nmounts, sizeof(mounts[0]),
>>>> +          lxcContainerChildMountSort);
>>>>
>>>>       for (i = 0 ; i<   nmounts ; i++) {
>>>>           VIR_DEBUG("Umount %s", mounts[i]);
>>> NACK, the check for NULL is correct
>>>
>>>
>>> Daniel
>> Hi Daniel,
>> My comment is wrong, but the following judgement should make sure
>> mounts is non null:
>> <snip>
>>          if (!(mounts[nmounts++] = strdup(mntent.mnt_dir))) {
If the previous VIR_REALLOC_N can't make sure 'mounts' is non null,
whether we need to check 'mounts' to avoid dereferencing a NULL
pointer in here again, for instance:

if (!mounts || !(mounts[nmounts++] = strdup(mntent.mnt_dir))) {

Thanks for your comment.

Alex

>>              endmntent(procmnt);
>>              virReportOOMError();
>>              return -1;
>>          }
>> </snip>
> That is ensuring that the pointer in the array element value is non-NULL.
> The "if (mounts) qsort(...)"  check is against the array itself, rather
> than the element.
>
> Regards,
> Daniel