[CRIU] [PATCH 1/2] IPC: message queue copy feature introduced

Pavel Emelyanov xemul at parallels.com
Thu Aug 9 04:47:32 EDT 2012


On 08/09/2012 12:40 PM, Stanislav Kinsbursky wrote:
> This patch is required for checkpoint/restore in userspace.
> IOW, c/r requires some way to get all pending IPC messages without deleting
> them from 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_COPY for sys_msgrcv() system call was
> introduced. Also, copy counter was added to msg_queue structure. It's set to
> zero by default and increases by one on each copy operation and decreased by
> one on each receive operation until reaches zero.

I think we should specify the copy_cnt semantics more strictly. How does
it correlate with message types?

> If MSG_COPY is set, then kernel will allocate dummy message with passed size,
> and then use new copy_msg() helper function to copy desired message (instead of
> unlinking it from the queue).
> 
> Signed-off-by: Stanislav Kinsbursky <skinsbursky at parallels.com>
> ---
>  include/linux/msg.h |    7 +++++++
>  ipc/msg.c           |   51 ++++++++++++++++++++++++++++++++++++++++++++++++---
>  ipc/msgutil.c       |   38 ++++++++++++++++++++++++++++++++++++++
>  ipc/util.h          |    1 +
>  4 files changed, 94 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/msg.h b/include/linux/msg.h
> index 9411b76..de739d1 100644
> --- a/include/linux/msg.h
> +++ b/include/linux/msg.h
> @@ -12,6 +12,10 @@
>  #define MSG_NOERROR     010000  /* no error if message is too big */
>  #define MSG_EXCEPT      020000  /* recv any msg except of specified type.*/
>  
> +#ifdef CONFIG_CHECKPOINT_RESTORE
> +#define MSG_COPY        040000  /* copy (not remove) all queue messages */
> +#endif
> +
>  /* Obsolete, used only for backwards compatibility and libc5 compiles */
>  struct msqid_ds {
>  	struct ipc_perm msg_perm;
> @@ -96,6 +100,9 @@ struct msg_queue {
>  	unsigned long q_qbytes;		/* max number of bytes on queue */
>  	pid_t q_lspid;			/* pid of last msgsnd */
>  	pid_t q_lrpid;			/* last receive pid */
> +#ifdef CONFIG_CHECKPOINT_RESTORE
> +	unsigned int q_copy_cnt;	/* message number for copy operations */
> +#endif
>  
>  	struct list_head q_messages;
>  	struct list_head q_receivers;
> diff --git a/ipc/msg.c b/ipc/msg.c
> index 08009f5..d4ca06f 100644
> --- a/ipc/msg.c
> +++ b/ipc/msg.c
> @@ -214,6 +214,9 @@ static int newque(struct ipc_namespace *ns, struct ipc_params *params)
>  	msq->q_cbytes = msq->q_qnum = 0;
>  	msq->q_qbytes = ns->msg_ctlmnb;
>  	msq->q_lspid = msq->q_lrpid = 0;
> +#ifdef CONFIG_CHECKPOINT_RESTORE
> +	msq->q_copy_cnt = 0;
> +#endif
>  	INIT_LIST_HEAD(&msq->q_messages);
>  	INIT_LIST_HEAD(&msq->q_receivers);
>  	INIT_LIST_HEAD(&msq->q_senders);
> @@ -784,19 +787,38 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp,
>  	struct msg_msg *msg;
>  	int mode;
>  	struct ipc_namespace *ns;
> +#ifdef CONFIG_CHECKPOINT_RESTORE
> +	struct msg_msg *copy = NULL;
> +#endif
>  
>  	if (msqid < 0 || (long) bufsz < 0)
>  		return -EINVAL;
>  	mode = convert_mode(&msgtyp, msgflg);
>  	ns = current->nsproxy->ipc_ns;
> -
> +#ifdef CONFIG_CHECKPOINT_RESTORE
> +	if (msgflg & MSG_COPY) {
> +		/*
> +		 * Create dummy message to copy real message to.
> +		 */
> +		copy = load_msg(buf, bufsz);
> +		if (IS_ERR(copy))
> +			return PTR_ERR(copy);
> +		copy->m_ts = bufsz;
> +	}
> +#endif
>  	msq = msg_lock_check(ns, msqid);
> -	if (IS_ERR(msq))
> +	if (IS_ERR(msq)) {
> +#ifdef CONFIG_CHECKPOINT_RESTORE
> +		if (msgflg & MSG_COPY)
> +			free_msg(copy);
> +#endif
>  		return PTR_ERR(msq);
> +	}
>  
>  	for (;;) {
>  		struct msg_receiver msr_d;
>  		struct list_head *tmp;
> +		int msg_counter = 0;
>  
>  		msg = ERR_PTR(-EACCES);
>  		if (ipcperms(ns, &msq->q_perm, S_IRUGO))
> @@ -816,12 +838,20 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp,
>  						walk_msg->m_type != 1) {
>  					msg = walk_msg;
>  					msgtyp = walk_msg->m_type - 1;
> +#ifdef CONFIG_CHECKPOINT_RESTORE
> +				} else if (msgflg & MSG_COPY) {
> +					if (msq->q_copy_cnt == msg_counter) {
> +						msg = copy_msg(walk_msg, copy);
> +						break;
> +					}
> +#endif
>  				} else {
>  					msg = walk_msg;
>  					break;
>  				}
>  			}
>  			tmp = tmp->next;
> +			msg_counter++;
>  		}
>  		if (!IS_ERR(msg)) {
>  			/*
> @@ -832,11 +862,21 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp,
>  				msg = ERR_PTR(-E2BIG);
>  				goto out_unlock;
>  			}
> +#ifdef CONFIG_CHECKPOINT_RESTORE
> +			if (msgflg & MSG_COPY) {
> +				msq->q_copy_cnt++;
> +				goto out_unlock;
> +			}
> +#endif
>  			list_del(&msg->m_list);
>  			msq->q_qnum--;
>  			msq->q_rtime = get_seconds();
>  			msq->q_lrpid = task_tgid_vnr(current);
>  			msq->q_cbytes -= msg->m_ts;
> +#ifdef CONFIG_CHECKPOINT_RESTORE
> +			if (msq->q_copy_cnt)
> +				msq->q_copy_cnt--;
> +#endif
>  			atomic_sub(msg->m_ts, &ns->msg_bytes);
>  			atomic_dec(&ns->msg_hdrs);
>  			ss_wakeup(&msq->q_senders, 0);
> @@ -915,8 +955,13 @@ out_unlock:
>  			break;
>  		}
>  	}
> -	if (IS_ERR(msg))
> +	if (IS_ERR(msg)) {
> +#ifdef CONFIG_CHECKPOINT_RESTORE
> +		if (msgflg & MSG_COPY)
> +			free_msg(copy);
> +#endif
>  		return PTR_ERR(msg);
> +	}
>  
>  	bufsz = msg_handler(buf, msg, bufsz);
>  	free_msg(msg);
> diff --git a/ipc/msgutil.c b/ipc/msgutil.c
> index 26143d3..b281f5c 100644
> --- a/ipc/msgutil.c
> +++ b/ipc/msgutil.c
> @@ -100,7 +100,45 @@ out_err:
>  	free_msg(msg);
>  	return ERR_PTR(err);
>  }
> +#ifdef CONFIG_CHECKPOINT_RESTORE
> +struct msg_msg *copy_msg(struct msg_msg *src, struct msg_msg *dst)
> +{
> +	struct msg_msgseg *dst_pseg, *src_pseg;
> +	int len = src->m_ts;
> +	int alen;
> +
> +	BUG_ON(dst == NULL);
> +	if (src->m_ts > dst->m_ts)
> +		return ERR_PTR(-EINVAL);
> +
> +	alen = len;
> +	if (alen > DATALEN_MSG)
> +		alen = DATALEN_MSG;
> +
> +	dst->next = NULL;
> +	dst->security = NULL;
>  
> +	memcpy(dst + 1, src + 1, alen);
> +
> +	len -= alen;
> +	dst_pseg = dst->next;
> +	src_pseg = src->next;
> +	while (len > 0) {
> +		alen = len;
> +		if (alen > DATALEN_SEG)
> +			alen = DATALEN_SEG;
> +		memcpy(dst_pseg + 1, src_pseg + 1, alen);
> +		dst_pseg = dst_pseg->next;
> +		len -= alen;
> +		src_pseg = src_pseg->next;
> +	}
> +
> +	dst->m_type = src->m_type;
> +	dst->m_ts = src->m_ts;
> +
> +	return dst;
> +}
> +#endif
>  int store_msg(void __user *dest, struct msg_msg *msg, int len)
>  {
>  	int alen;
> diff --git a/ipc/util.h b/ipc/util.h
> index 2bc6a9a..c1e1d5c 100644
> --- a/ipc/util.h
> +++ b/ipc/util.h
> @@ -142,6 +142,7 @@ int ipc_parse_version (int *cmd);
>  
>  extern void free_msg(struct msg_msg *msg);
>  extern struct msg_msg *load_msg(const void __user *src, int len);
> +extern struct msg_msg *copy_msg(struct msg_msg *src, struct msg_msg *dst);
>  extern int store_msg(void __user *dest, struct msg_msg *msg, int len);
>  
>  extern void recompute_msgmni(struct ipc_namespace *);
> 
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