Re: [PATCH v4 09/11] nfsdcld: reopen pipe if it's deleted and recreated

[Steve Dickson <SteveD@redhat.com>]

On 01/25/2012 06:32 PM, Jeff Layton wrote:
> On Wed, 25 Jan 2012 17:04:44 -0500
> Steve Dickson <SteveD@redhat.com> wrote:
> 
>>
>>
>> On 01/25/2012 03:28 PM, Jeff Layton wrote:
>>> On Wed, 25 Jan 2012 14:31:10 -0500
>>> Steve Dickson <SteveD@redhat.com> wrote:
>>>
>>>>
>>>>
>>>> On 01/25/2012 02:09 PM, Jeff Layton wrote:
>>>>> On Wed, 25 Jan 2012 13:16:24 -0500
>>>>> Steve Dickson <SteveD@redhat.com> wrote:
>>>>>
>>>>>> Hey Jeff,
>>>>>>
>>>>>> Commit inline... 
>>>>>>
>>>>>> On 01/23/2012 03:02 PM, Jeff Layton wrote:
>>>>>>> This can happen if nfsd is shut down and restarted. If that occurs,
>>>>>>> then reopen the pipe so we're not waiting for data on the defunct
>>>>>>> pipe.
>>>>>>>
>>>>>>> Signed-off-by: Jeff Layton <jlayton@redhat.com>
>>>>>>> ---
>>>>>>>  utils/nfsdcld/nfsdcld.c |   84 +++++++++++++++++++++++++++++++++++++++++-----
>>>>>>>  1 files changed, 74 insertions(+), 10 deletions(-)
>>>>>>>
>>>>>>> diff --git a/utils/nfsdcld/nfsdcld.c b/utils/nfsdcld/nfsdcld.c
>>>>>>> index b0c08e2..0dc5b37 100644
>>>>>>> --- a/utils/nfsdcld/nfsdcld.c
>>>>>>> +++ b/utils/nfsdcld/nfsdcld.c
>>>>>>> @@ -57,6 +57,8 @@ struct cld_client {
>>>>>>>  
>>>>>>>  /* global variables */
>>>>>>>  static char *pipepath = DEFAULT_CLD_PATH;
>>>>>>> +static int 		inotify_fd = -1;
>>>>>>> +static struct event	pipedir_event;
>>>>>>>  
>>>>>>>  static struct option longopts[] =
>>>>>>>  {
>>>>>>> @@ -68,8 +70,10 @@ static struct option longopts[] =
>>>>>>>  	{ NULL, 0, 0, 0 },
>>>>>>>  };
>>>>>>>  
>>>>>>> +
>>>>>>>  /* forward declarations */
>>>>>>>  static void cldcb(int UNUSED(fd), short which, void *data);
>>>>>>> +static void cld_pipe_reopen(struct cld_client *clnt);
>>>>>>>  
>>>>>>>  static void
>>>>>>>  usage(char *progname)
>>>>>>> @@ -80,10 +84,62 @@ usage(char *progname)
>>>>>>>  
>>>>>>>  #define INOTIFY_EVENT_MAX (sizeof(struct inotify_event) + NAME_MAX)
>>>>>>>  
>>>>>>> +static void
>>>>>>> +cld_inotify_cb(int UNUSED(fd), short which, void *data)
>>>>>>> +{
>>>>>>> +	int ret, oldfd;
>>>>>>> +	char evbuf[INOTIFY_EVENT_MAX];
>>>>>>> +	char *dirc = NULL, *pname;
>>>>>>> +	struct inotify_event *event = (struct inotify_event *)evbuf;
>>>>>>> +	struct cld_client *clnt = data;
>>>>>>> +
>>>>>>> +	if (which != EV_READ)
>>>>>>> +		return;
>>>>>>> +
>>>>>>> +	dirc = strndup(pipepath, PATH_MAX);
>>>>>>> +	if (!dirc) {
>>>>>>> +		xlog_err("%s: unable to allocate memory", __func__);
>>>>>>> +		goto out;
>>>>>>> +	}
>>>>>>> +
>>>>>>> +	ret = read(inotify_fd, evbuf, INOTIFY_EVENT_MAX);
>>>>>>> +	if (ret < 0) {
>>>>>>> +		xlog_err("%s: read from inotify fd failed: %m", __func__);
>>>>>>> +		goto out;
>>>>>>> +	}
>>>>>>> +
>>>>>>> +	/* check to see if we have a filename in the evbuf */
>>>>>>> +	if (!event->len)
>>>>>>> +		goto out;
>>>>>>> +
>>>>>>> +	pname = basename(dirc);
>>>>>>> +
>>>>>>> +	/* does the filename match our pipe? */
>>>>>>> +	if (strncmp(pname, event->name, event->len))
>>>>>>> +		goto out;
>>>>>>> +
>>>>>>> +	/*
>>>>>>> +	 * reopen the pipe. The old fd is not closed until the new one is
>>>>>>> +	 * opened, so we know they should be different if the reopen is
>>>>>>> +	 * successful.
>>>>>>> +	 */
>>>>>>> +	oldfd = clnt->cl_fd;
>>>>>>> +	do {
>>>>>>> +		cld_pipe_reopen(clnt);
>>>>>>> +	} while (oldfd == clnt->cl_fd);
>>>>>> Doesn't this have a potential for an infinite loop? 
>>>>>>
>>>>>> steved.  
>>>>>
>>>>>
>>>>> Yes. If reopening the new pipe continually fails then it will loop
>>>>> forever.
>>>> Would it be more accurate to say it would be spinning forever? 
>>>> Since there is no sleep or delay in cld_pipe_reopen, what's
>>>> going to stop the daemon from spinning in a CPU bound loop?
>>>>
>>>
>>> Well, not spinning in a userspace loop...it'll continually be cycling on
>>> an open() call that's not working for whatever reason. We sort of have
>>> to loop on that though. I think the best we can do is add a sleep(1) in
>>> there or something. Would that be sufficient?
>>>
>> I still think it going to needlessly suck up CPU cycles... 
>>
>> The way I handled this in the rpc.idmapd daemon was to do the
>> reopen on a SIGHUP signal. Then in NFS server initscript 
>> I did the following:
>>     /usr/bin/pkill -HUP rpc.idmapd
>>
>> Thoughts?
>>
> 
> Ugh, that requires manual intervention if the pipe is removed and
> recreated. If someone restarts nfsd and doesn't send the signal, then
> they won't get the upcalls. I'd prefer something that "just works".
I have not seen any bz open saying rpc.idmapd doesn't just work... 

> 
> Seriously, is it that big a deal to just loop here? One open(2) call
> every second doesn't seem that bad, and honestly if a new pipe pops up
> and the daemon can't open it then a few CPU cycles is the least of your
> worries.
> 
Put the daemon in that loop and then run the top command in another 
window.. If the daemon is at the top of the list then it is a big
deal because that daemon will on the top forever for no reason, in
the cast of the NFS server not coming back. 

tia,

steved.