Re: [PATCH] IPC: message queue stealing feature introduced

Eric Dumazet
2012-02-15T09:40:20Z

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)