From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Vrabel <david.vrabel@citrix.com>
Subject: Re: [PATCHv1 3/6] evtchn: simplify port_is_valid()
Date: Tue, 9 Jun 2015 16:16:52 +0100
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To: Andrew Cooper <andrew.cooper3@citrix.com>, David Vrabel <david.vrabel@citrix.com>, xen-devel@lists.xenproject.org
Cc: Keir Fraser <keir@xen.org>, Tim Deegan <tim@xen.org>, Ian Campbell <ian.campbell@citrix.com>, Jan Beulich <jbeulich@suse.com>
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On 09/06/15 16:08, Andrew Cooper wrote:
> On 09/06/15 15:59, David Vrabel wrote:
>> By keeping a count of the number of currently valid event channels,
>> port_is_valid() can be simplified.
>>
>> d->valid_evtchns can also be tested without holding d->event_lock which
>> will be useful later on.
[...]
>> --- a/xen/include/xen/sched.h
>> +++ b/xen/include/xen/sched.h
>> @@ -336,8 +336,9 @@ struct domain
>>      /* Event channel information. */
>>      struct evtchn   *evtchn;                         /* first bucket only */
>>      struct evtchn  **evtchn_group[NR_EVTCHN_GROUPS]; /* all other buckets */
>> -    unsigned int     max_evtchns;
>> -    unsigned int     max_evtchn_port;
>> +    unsigned int     max_evtchns;     /* number supported by ABI */
>> +    unsigned int     max_evtchn_port; /* max permitted port number */
>> +    atomic_t         valid_evtchns;   /* number of allocated event channels */
> 
> atomic_t contains a signed integer.  You probably want a BUILD_BUG_ON()
> if any ABI maximum value exceeds INT_MAX.

Probably better to use unsigned int and read_atomic().  All the updates
to valid_evtchns are done while holding d->event_lock.

David

ps. please trim replies.