linux-kernel - Re: [PATCH] IPC: message queue stealing feature introduced

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Date:	Wed, 15 Feb 2012 19:02:20 +0400
From:	Stanislav Kinsbursky <skinsbursky@...allels.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"criu@...nvz.org" <criu@...nvz.org>,
	"lucas.demarchi@...fusion.mobi" <lucas.demarchi@...fusion.mobi>,
	"dhowells@...hat.com" <dhowells@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"serge.hallyn@...onical.com" <serge.hallyn@...onical.com>
Subject: Re: [PATCH] IPC: message queue stealing feature introduced

15.02.2012 13:40, Eric Dumazet пишет:
> Le mercredi 15 février 2012 à 13:08 +0400, Stanislav Kinsbursky a
> écrit :
>> This patch is required for checkpoint/restore in userspace project.
>> C/r requires some way to get all pending IPC messages without deleting them for
>> the queue (checkpoint can fail and in this case tasks will be resumed, so queue
>> have to be valid).
>> To achive this, new operation flag MSG_STEAL for sys_msgrcv() system call
>> introduced.
>> If this flag is set, then passed struct msgbuf pointer will be used for storing
>> array of structures:
>>
>> struct msgbuf_a {
>> 	long mtype;         /* type of message */
>> 	size_t msize;       /* size of message */
>> 	char mtext[0];      /* message text */
>> };
>>
>
> This structure is not 32/64 bit safe and will need compat tricks.
>
> +                       ret = do_steal_msg(mtext, arrsz, msg);
> +                       if (ret<  0) {
> +                               msg = ERR_PTR(ret);
> +                               goto out_unlock;
> +                       }
> +                       mtext += ret + sizeof(struct msgbuf_a);
> +                       arrsz -= ret + sizeof(struct msgbuf_a);
>
> I cant see where alignement requirements are met.
>
> (ret should be rounded up to a multiple of alignof(struct msgbuf_a)
>


Thanks for reply, Eric.
Will fix and resend soon.

-- 
Best regards,
Stanislav Kinsbursky
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