[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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