[CRIU] [PATCH 1/2] IPC: message queue copy feature introduced
Stanislav Kinsbursky
skinsbursky at parallels.com
Thu Aug 9 06:21:24 EDT 2012
09.08.2012 13:53, Pavel Emelyanov пишет:
> On 08/09/2012 01:25 PM, Stanislav Kinsbursky wrote:
>> 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.
>
> That's exactly what I asked -- this number is the n-th message of desired type,
> thanks.
>
> Next issue: I'm bothered by the amount of #ifdef-s over the code.
>
Me too. Any simple solutions?
Rewrite all the logic to reduce #ifdef-s count is unacceptable.
>>>> 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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>>>
>>
>>
>
--
Best regards,
Stanislav Kinsbursky
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