[libvirt] [PATCH] util: change virFile*Pid functions to return < 0 on failure

Laine Stump laine at laine.org
Mon Jul 25 20:59:41 UTC 2011

On 07/25/2011 03:17 PM, Eric Blake wrote:
> On 07/25/2011 12:19 PM, Laine Stump wrote:
>> Although most functions in libvirt return 0 on success and<  0 on
>> failure, there are a few functions lingering around that return errno
>> (a positive value) on failure, and sometimes code calling those
>> functions incorrectly assumes the<0 standard. I noticed one of these
>> the other day when auditing networkStartDhcpDaemon after Guido Gunther
>> found a place where success was improperly returned on failure (that
>> patch has been acked and is pending a push). The problem was that it
>> expected the return value from virFileReadPid to be<  0 on failure,
>> but it was actually positive (it was also neglected to set the return
>> code in this case, similar to the bug found by Guido).
>> This all led to the fact that *all* of the virFile*Pid functions in
>> util.c are returning errno on failure. This patch remedies that
>> problem by changing them all to return -errno on failure, and makes
>> any necessary changes to callers of the functions. (In the meantime, I
>> also properly set the return code on failure of virFileReadPid in
>> networkStartDhcpDaemon).
>> +++ b/src/lxc/lxc_controller.c
>> @@ -996,5 +996,5 @@ cleanup:
>>           unlink(sockpath);
>>       VIR_FREE(sockpath);
>> -    return rc;
>> +    return -rc; /* rc is 0 or negative, but returns from main should 
>> be>=0 */
> This hunk is wrong.  errno can validly be a multiple of 256, in which 
> case this results in the program exiting with status 0 instead of an 
> error.  There's no portable way to use errno as a program's exit 
> status.  Rather, this should be:
> so that we are guaranteed that main() exits with a non-zero positive 
> value on failure that cannot wrap around.
> ACK to the patch with that problem fixed.

Thanks! I made the change and pushed.

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