ipc: introduce message queue copy feature

This patch is required for checkpoint/restore in userspace.

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.  If this flag was specified, then mtype is interpreted as
number of the message to copy.

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).

Notes:

1) Return -ENOSYS if MSG_COPY is specified, but
   CONFIG_CHECKPOINT_RESTORE is not set.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Cc: Serge Hallyn <serge.hallyn@canonical.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/uapi/linux/msg.h b/include/uapi/linux/msg.h
index 78dbd2f996a3668665718e5dcad7918966640281..22d95c6854e0cb0fbadaafae1c681ed9ad805780 100644 (file)
--- a/include/uapi/linux/msg.h
+++ b/include/uapi/linux/msg.h
@@ -10,6 +10,7 @@
 /* msgrcv options */
 #define MSG_NOERROR     010000  /* no error if message is too big */
 #define MSG_EXCEPT      020000  /* recv any msg except of specified type.*/
+#define MSG_COPY        040000  /* copy (not remove) all queue messages */
 
 /* Obsolete, used only for backwards compatibility and libc5 compiles */
 struct msqid_ds {

diff --git a/ipc/msg.c b/ipc/msg.c
index cefc24f46e3e39936a2f6d1993a83da5b14e4389..889cc8db39576b97726bbba4dd4494de15800c33 100644 (file)
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -777,19 +777,48 @@ 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;
+       unsigned long copy_number = 0;
+#endif
 
        if (msqid < 0 || (long) bufsz < 0)
                return -EINVAL;
+       if (msgflg & MSG_COPY) {
+#ifdef CONFIG_CHECKPOINT_RESTORE
+
+               if (msgflg & MSG_COPY) {
+                       copy_number = msgtyp;
+                       msgtyp = 0;
+               }
+
+               /*
+                * 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;
+#else
+               return -ENOSYS;
+#endif
+       }
        mode = convert_mode(&msgtyp, msgflg);
        ns = current->nsproxy->ipc_ns;
 
        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;
+               long msg_counter = 0;
 
                msg = ERR_PTR(-EACCES);
                if (ipcperms(ns, &msq->q_perm, S_IRUGO))
@@ -809,8 +838,16 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp,
                                if (mode == SEARCH_LESSEQUAL &&
                                                walk_msg->m_type != 1) {
                                        msgtyp = walk_msg->m_type - 1;
+#ifdef CONFIG_CHECKPOINT_RESTORE
+                               } else if (msgflg & MSG_COPY) {
+                                       if (copy_number == msg_counter) {
+                                               msg = copy_msg(walk_msg, copy);
+                                               break;
+                                       }
+#endif
                                } else
                                        break;
+                               msg_counter++;
                        }
                        tmp = tmp->next;
                }
@@ -823,6 +860,10 @@ 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)
+                               goto out_unlock;
+#endif
                        list_del(&msg->m_list);
                        msq->q_qnum--;
                        msq->q_rtime = get_seconds();
@@ -906,8 +947,13 @@ 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 26143d377c951be9fd5e855074d431707bfd9f10..b281f5cc0057ce7101cc6d01e8fad0847f2538d2 100644 (file)
--- 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 a61e0ca2bffd05c0d3d5dd390df95e140a4b4186..eeb79a1fbd834eda23027624824faf94bfb2f459 100644 (file)
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -140,6 +140,7 @@ 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 *);