Re: [PATCH 4/6] osd_client, rbd: update event interface for watch/notify2

From: Douglas Fuller <dfuller@redhat.com>
To: Josh Durgin <jdurgin@redhat.com>
Cc: ceph-devel@vger.kernel.org
Subject: Re: [PATCH 4/6] osd_client, rbd: update event interface for watch/notify2
Date: Wed, 17 Jun 2015 09:28:35 -0400	[thread overview]
Message-ID: <16ACAFCB-0E28-4762-BDF9-E68B7FE5D817@redhat.com> (raw)
In-Reply-To: <5580AEC9.9020908@redhat.com>

> On Jun 16, 2015, at 7:18 PM, Josh Durgin <jdurgin@redhat.com> wrote:
> 
> On 06/12/2015 08:56 AM, Douglas Fuller wrote:
>> 
>> @@ -3132,6 +3132,26 @@ static void rbd_watch_cb(u64 ver, u64 notify_id, u8 opcode, s32 return_code,
>>  		rbd_warn(rbd_dev, "notify_ack ret %d", ret);
>>  }
>> 
>> +static void rbd_watch_error_cb(void *arg, u64 cookie, int err)
>> +{
>> +	struct rbd_device *rbd_dev = (struct rbd_device *)arg;
>> +	int ret;
>> +
>> +	dout("%s: watch error %d on cookie %llu\n", rbd_dev->header_name,
>> +		err, cookie);
>> +	rbd_warn(rbd_dev, "%s: watch error %d on cookie %llu\n",
>> +	         rbd_dev->header_name, err, cookie);
>> +
>> +	/* reset watch */
>> +	rbd_dev_refresh(rbd_dev);
>> +	rbd_dev_header_unwatch_sync(rbd_dev);
>> +	ret = rbd_dev_header_watch_sync(rbd_dev);
>> +	BUG_ON(ret); /* XXX: was the image deleted? can we be more graceful? */
>> +	rbd_dev_refresh(rbd_dev);
> 
> Why refresh before and after unwatching? Only the second one seems
> necessary.

The first one isn’t strictly necessary; I can remove it if you want.

If we get a watch error, we may very well have a situation in which we need to stop I/O to the device because the underlying image has been deleted or its features have changed. We don’t actually do that yet (we just print a warning message), but the extra refresh was to handle that case early, even before we bothered trying to re-establish the watch.--
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