X-Git-Url: http://git.onelab.eu/?a=blobdiff_plain;f=include%2Flinux%2Fpid.h;h=9777d96ee80748a725424eb9cf426da196de625f;hb=refs%2Fheads%2Fvserver;hp=5e46c1d4e1b479419ba3dfe15aa8b1e9688dbb62;hpb=76828883507a47dae78837ab5dec5a5b4513c667;p=linux-2.6.git

diff --git a/include/linux/pid.h b/include/linux/pid.h
index 5e46c1d4e..9777d96ee 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -1,56 +1,135 @@
 #ifndef _LINUX_PID_H
 #define _LINUX_PID_H
 
+#include <linux/rcupdate.h>
+
 enum pid_type
 {
 	PIDTYPE_PID,
-	PIDTYPE_TGID,
 	PIDTYPE_PGID,
 	PIDTYPE_SID,
 	PIDTYPE_MAX,
 	PIDTYPE_REALPID
 };
 
+/*
+ * What is struct pid?
+ *
+ * A struct pid is the kernel's internal notion of a process identifier.
+ * It refers to individual tasks, process groups, and sessions.  While
+ * there are processes attached to it the struct pid lives in a hash
+ * table, so it and then the processes that it refers to can be found
+ * quickly from the numeric pid value.  The attached processes may be
+ * quickly accessed by following pointers from struct pid.
+ *
+ * Storing pid_t values in the kernel and refering to them later has a
+ * problem.  The process originally with that pid may have exited and the
+ * pid allocator wrapped, and another process could have come along
+ * and been assigned that pid.
+ *
+ * Referring to user space processes by holding a reference to struct
+ * task_struct has a problem.  When the user space process exits
+ * the now useless task_struct is still kept.  A task_struct plus a
+ * stack consumes around 10K of low kernel memory.  More precisely
+ * this is THREAD_SIZE + sizeof(struct task_struct).  By comparison
+ * a struct pid is about 64 bytes.
+ *
+ * Holding a reference to struct pid solves both of these problems.
+ * It is small so holding a reference does not consume a lot of
+ * resources, and since a new struct pid is allocated when the numeric pid
+ * value is reused (when pids wrap around) we don't mistakenly refer to new
+ * processes.
+ */
+
 struct pid
 {
+	atomic_t count;
 	/* Try to keep pid_chain in the same cacheline as nr for find_pid */
 	int nr;
 	struct hlist_node pid_chain;
-	/* list of pids with the same nr, only one of them is in the hash */
-	struct list_head pid_list;
+	/* lists of tasks that use this pid */
+	struct hlist_head tasks[PIDTYPE_MAX];
+	struct rcu_head rcu;
+};
+
+struct pid_link
+{
+	struct hlist_node node;
+	struct pid *pid;
 };
 
-#define pid_task(elem, type) \
-	list_entry(elem, struct task_struct, pids[type].pid_list)
+static inline struct pid *get_pid(struct pid *pid)
+{
+	if (pid)
+		atomic_inc(&pid->count);
+	return pid;
+}
+
+extern void FASTCALL(put_pid(struct pid *pid));
+extern struct task_struct *FASTCALL(pid_task(struct pid *pid, enum pid_type));
+extern struct task_struct *FASTCALL(get_pid_task(struct pid *pid,
+						enum pid_type));
+
+extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
 
 /*
  * attach_pid() and detach_pid() must be called with the tasklist_lock
  * write-held.
  */
-extern int FASTCALL(attach_pid(struct task_struct *task, enum pid_type type, int nr));
+extern int FASTCALL(attach_pid(struct task_struct *task,
+				enum pid_type type, int nr));
 
 extern void FASTCALL(detach_pid(struct task_struct *task, enum pid_type));
+extern void FASTCALL(transfer_pid(struct task_struct *old,
+				  struct task_struct *new, enum pid_type));
 
 /*
  * look up a PID in the hash table. Must be called with the tasklist_lock
- * held.
+ * or rcu_read_lock() held.
  */
-extern struct pid *FASTCALL(find_pid(enum pid_type, int));
+extern struct pid *FASTCALL(find_pid(int nr));
+
+/*
+ * Lookup a PID in the hash table, and return with it's count elevated.
+ */
+extern struct pid *find_get_pid(int nr);
+extern struct pid *find_ge_pid(int nr);
+
+extern struct pid *alloc_pid(void);
+extern void FASTCALL(free_pid(struct pid *pid));
+
+static inline pid_t pid_nr(struct pid *pid)
+{
+	pid_t nr = 0;
+	if (pid)
+		nr = pid->nr;
+	return nr;
+}
 
-extern int alloc_pidmap(void);
-extern void FASTCALL(free_pidmap(int));
-extern void switch_exec_pids(struct task_struct *leader, struct task_struct *thread);
 
 #define do_each_task_pid(who, type, task)				\
-	if ((task = find_task_by_pid_type(type, who))) {		\
-		prefetch((task)->pids[type].pid_list.next);		\
-		do {
+	do {								\
+		struct hlist_node *pos___;				\
+		struct pid *pid___ = find_pid(who);			\
+		if (pid___ != NULL)					\
+			hlist_for_each_entry_rcu((task), pos___,	\
+				&pid___->tasks[type], pids[type].node) {
 
 #define while_each_task_pid(who, type, task)				\
-		} while (task = pid_task((task)->pids[type].pid_list.next,\
-						type),			\
-			prefetch((task)->pids[type].pid_list.next),	\
-			hlist_unhashed(&(task)->pids[type].pid_chain));	\
-	}								\
+			}						\
+	} while (0)
+
+
+#define do_each_pid_task(pid, type, task)				\
+	do {								\
+		struct hlist_node *pos___;				\
+		if (pid != NULL)					\
+			hlist_for_each_entry_rcu((task), pos___,	\
+				&pid->tasks[type], pids[type].node)	\
+			if (vx_check((task)->xid, VS_ADMIN_P|VS_IDENT)) {
+
+#define while_each_pid_task(pid, type, task)				\
+			}						\
+	} while (0)
 
 #endif /* _LINUX_PID_H */