[CRIU] [PATCH 1/2] IPC: message queue copy feature introduced
Stanislav Kinsbursky
skinsbursky at parallels.com
Thu Aug 9 05:25:59 EDT 2012
09.08.2012 12:47, Pavel Emelyanov пишет:
> 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?
>
What do you mean?
It doesn't correlate at all - syscall logic remains the same.
I.e. if you specify message type, then you'll copy n-th message on desired type.
>> 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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>> https://openvz.org/mailman/listinfo/criu
>
--
Best regards,
Stanislav Kinsbursky
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