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Re: [libvirt] [PATCH] file: Log closing filedescriptors



On 05/30/2012 08:56 AM, Jiri Denemark wrote:
> On Wed, May 30, 2012 at 08:48:22 -0600, Eric Blake wrote:
>> On 05/30/2012 08:34 AM, Jiri Denemark wrote:
>>> ---
>>>  src/util/virfile.c |   10 ++++++++++
>>>  1 file changed, 10 insertions(+)
>>>
>>> diff --git a/src/util/virfile.c b/src/util/virfile.c
>>> index db3d737..bc7f2c9 100644
>>> --- a/src/util/virfile.c
>>> +++ b/src/util/virfile.c
>>> @@ -35,6 +35,7 @@
>>>  #include "configmake.h"
>>>  #include "memory.h"
>>>  #include "virterror_internal.h"
>>> +#include "logging.h"
>>>  
>>>  #define VIR_FROM_THIS VIR_FROM_NONE
>>>  #define virFileError(code, ...)                                   \
>>> @@ -51,6 +52,15 @@ int virFileClose(int *fdptr, bool preserve_errno)
>>>          if (preserve_errno)
>>>              saved_errno = errno;
>>>          rc = close(*fdptr);
>>> +        if (rc < 0) {
>>> +            if (errno != EBADF) {
>>> +                char ebuf[1024] ATTRIBUTE_UNUSED;
>>> +                VIR_DEBUG("Failed to close fd %d: %d",
>>> +                          *fdptr, virStrerror(errno, ebuf, sizeof(ebuf)));
>>
>> I think we _also_ need to log EBADF errors, those are usually the sign
>> of developer bugs, as you are probably guilty of a double-close race.
>> In fact, I think EBADF should be logged with higher severity than
>> VIR_DEBUG, as we want to see that right away.
> 
> I explicitly didn't want to log them since you would see a lot of errors when
> after fork we are closing all available file descriptors except those we
> explicitly want to leave open... I'll add EBADF logging and handle those
> mass-closes separately.

Oh, good point.  EBADF in the parent is almost always a bug (and if the
race had gone the other way, you'd have a double-close).  EBADF in the
child is an annoyance - we know we are single-threaded and therefore
there is no double-close race, and it is more efficient to try and waste
a close() than it is to do an fcntl() filter to see if the fd is valid
in order to decide whether to close.

But that means that the _only_ place that should be ignoring EBADF on a
mass-close is in the post-fork() closing of a child; so maybe the
solution is:

change the signature of virFileClose() to take an extra parameter to say
whether to ignore EBADF,

change VIR_FORCE_CLOSE to pass false to the new parameter,

and change command.c's mass-close to use virFileClose() directly, with
the parameter set to true

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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