On Wed, May 27, 2009 at 01:32:45PM -0400, Oren Laadan wrote:

Now we can do "external" checkpoint, i.e. act on another task.

+static int may_checkpoint_task(struct ckpt_ctx *ctx, struct task_struct *t)
+{
+	if (t->state == TASK_DEAD) {
+		pr_warning("c/r: task %d is TASK_DEAD\n", task_pid_vnr(t));
+		return -EAGAIN;
+	}
+
+	if (!ptrace_may_access(t, PTRACE_MODE_READ)) {
+		__ckpt_write_err(ctx, "access to task %d (%s) denied",
+				 task_pid_vnr(t), t->comm);
+		return -EPERM;
+	}
+
+	/* verify that the task is frozen (unless self) */
+	if (t != current && !frozen(t)) {
+		__ckpt_write_err(ctx, "task %d (%s) is not frozen",
+				 task_pid_vnr(t), t->comm);
+		return -EBUSY;
+	}
+
+	/* FIX: add support for ptraced tasks */
+	if (task_ptrace(t)) {
+		__ckpt_write_err(ctx, "task %d (%s) is ptraced",
+				 task_pid_vnr(t), t->comm);
+		return -EBUSY;
+	}
+
+	return 0;
+}
+
+static int get_container(struct ckpt_ctx *ctx, pid_t pid)
+{
+	struct task_struct *task = NULL;
+	struct nsproxy *nsproxy = NULL;
+	int ret;
+
+	ctx->root_pid = pid;
+
+	read_lock(&tasklist_lock);
+	task = find_task_by_vpid(pid);
+	if (task)
+		get_task_struct(task);
+	read_unlock(&tasklist_lock);
+
+	if (!task)
+		return -ESRCH;
+
+	ret = may_checkpoint_task(ctx, task);
+	if (ret) {
+		ckpt_write_err(ctx, NULL);
+		put_task_struct(task);
+		return ret;
+	}
+
+	rcu_read_lock();
+	nsproxy = task_nsproxy(task);
+	get_nsproxy(nsproxy);

Will oops if init is multi-threaded and thread group leader exited
(nsproxy = NULL). I need to think what to do, too.

+	rcu_read_unlock();
+
+	ctx->root_task = task;
+	ctx->root_nsproxy = nsproxy;
+
+	return 0;
+}

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