[PATCH 2.6.24-rc8-mm1 09/15] (RFC) IPC: new kernel API to change an ID

[pierre.peiffer-6ktuUTfB/bM@public.gmane.org]

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From: Pierre Peiffer <pierre.peiffer-6ktuUTfB/bM@public.gmane.org>

This patch provides three new API to change the ID of an existing
System V IPCs.

These APIs are:
	long msg_chid(struct ipc_namespace *ns, int id, int newid);
	long sem_chid(struct ipc_namespace *ns, int id, int newid);
	long shm_chid(struct ipc_namespace *ns, int id, int newid);

They return 0 or an error code in case of failure.

They may be useful for setting a specific ID for an IPC when preparing
a restart operation.

To be successful, the following rules must be respected:
- the IPC exists (of course...)
- the new ID must satisfy the ID computation rule.
- the entry in the idr corresponding to the new ID must be free.

Signed-off-by: Pierre Peiffer <pierre.peiffer-6ktuUTfB/bM@public.gmane.org>
Acked-by: Serge Hallyn <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
---

 include/linux/msg.h |    2 ++
 include/linux/sem.h |    2 ++
 include/linux/shm.h |    3 +++
 ipc/msg.c           |   45 +++++++++++++++++++++++++++++++++++++++++++++
 ipc/sem.c           |   51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 ipc/shm.c           |   45 +++++++++++++++++++++++++++++++++++++++++++++
 ipc/util.c          |   48 ++++++++++++++++++++++++++++++++++++++++++++++++
 ipc/util.h          |    1 +
 8 files changed, 197 insertions(+)

Index: b/include/linux/msg.h
===================================================================
--- a/include/linux/msg.h
+++ b/include/linux/msg.h
@@ -63,6 +63,7 @@ struct msginfo {
 
 #ifdef __KERNEL__
 #include <linux/list.h>
+#include <linux/ipc_namespace.h>
 
 /* one msg_msg structure for each message */
 struct msg_msg {
@@ -96,6 +97,7 @@ extern long do_msgsnd(int msqid, long mt
 			size_t msgsz, int msgflg);
 extern long do_msgrcv(int msqid, long *pmtype, void __user *mtext,
 			size_t msgsz, long msgtyp, int msgflg);
+long msg_chid(struct ipc_namespace *ns, int id, int newid);
 
 #endif /* __KERNEL__ */
 
Index: b/include/linux/sem.h
===================================================================
--- a/include/linux/sem.h
+++ b/include/linux/sem.h
@@ -138,9 +138,11 @@ struct sysv_sem {
 };
 
 #ifdef CONFIG_SYSVIPC
+#include <linux/ipc_namespace.h>
 
 extern int copy_semundo(unsigned long clone_flags, struct task_struct *tsk);
 extern void exit_sem(struct task_struct *tsk);
+long sem_chid(struct ipc_namespace *ns, int id, int newid);
 
 #else
 static inline int copy_semundo(unsigned long clone_flags, struct task_struct *tsk)
Index: b/include/linux/shm.h
===================================================================
--- a/include/linux/shm.h
+++ b/include/linux/shm.h
@@ -104,8 +104,11 @@ struct shmid_kernel /* private to the ke
 #define SHM_NORESERVE   010000  /* don't check for reservations */
 
 #ifdef CONFIG_SYSVIPC
+#include <linux/ipc_namespace.h>
+
 long do_shmat(int shmid, char __user *shmaddr, int shmflg, unsigned long *addr);
 extern int is_file_shm_hugepages(struct file *file);
+long shm_chid(struct ipc_namespace *ns, int id, int newid);
 #else
 static inline long do_shmat(int shmid, char __user *shmaddr,
 				int shmflg, unsigned long *addr)
Index: b/ipc/msg.c
===================================================================
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -291,6 +291,51 @@ asmlinkage long sys_msgget(key_t key, in
 	return ipcget(ns, &msg_ids(ns), &msg_ops, &msg_params);
 }
 
+/* must be called with mutex and msq locks held */
+static long msg_chid_nolock(struct ipc_namespace *ns, struct msg_queue *msq,
+			    int newid)
+{
+	long err;
+
+	err = ipc_chid(&msg_ids(ns), msq->q_perm.id, newid);
+	if (!err)
+		msq->q_ctime = get_seconds();
+
+	return err;
+}
+
+/* API to use for changing an id from kernel space, not from the syscall, as
+   there is no permission check done here */
+long msg_chid(struct ipc_namespace *ns, int id, int newid)
+{
+	long err;
+	struct msg_queue *msq;
+
+retry:
+	err = idr_pre_get(&msg_ids(ns).ipcs_idr, GFP_KERNEL);
+	if (!err)
+		return -ENOMEM;
+
+	down_write(&msg_ids(ns).rw_mutex);
+	msq = msg_lock_check(ns, id);
+
+	if (IS_ERR(msq)) {
+		up_write(&msg_ids(ns).rw_mutex);
+		return PTR_ERR(msq);
+	}
+
+	err = msg_chid_nolock(ns, msq, newid);
+
+	msg_unlock(msq);
+	up_write(&msg_ids(ns).rw_mutex);
+
+	/* ipc_chid may return -EAGAIN in case of memory requirement */
+	if (err == -EAGAIN)
+		goto retry;
+
+	return err;
+}
+
 static inline unsigned long
 copy_msqid_to_user(void __user *buf, struct msqid64_ds *in, int version)
 {
Index: b/ipc/sem.c
===================================================================
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -564,6 +564,57 @@ static void freeary(struct ipc_namespace
 	ipc_rcu_putref(sma);
 }
 
+/* must be called with rw_mutex and sma locks held */
+static long sem_chid_nolock(struct ipc_namespace *ns, struct sem_array *sma,
+			    int newid)
+{
+	long err;
+
+	err = ipc_chid(&sem_ids(ns), sma->sem_perm.id, newid);
+
+	if (!err) {
+		struct sem_undo *un;
+		for (un = sma->undo; un; un = un->id_next)
+			un->semid = newid;
+
+		sma->sem_ctime = get_seconds();
+	}
+
+	return err;
+}
+
+/* API to use for changing an id from kernel space, not from the syscall, as
+   there is no permission check done here */
+long sem_chid(struct ipc_namespace *ns, int id, int newid)
+{
+	long err;
+	struct sem_array *sma;
+
+retry:
+	err = idr_pre_get(&sem_ids(ns).ipcs_idr, GFP_KERNEL);
+	if (!err)
+		return -ENOMEM;
+
+	down_write(&sem_ids(ns).rw_mutex);
+	sma = sem_lock_check(ns, id);
+
+	if (IS_ERR(sma)) {
+		up_write(&sem_ids(ns).rw_mutex);
+		return PTR_ERR(sma);
+	}
+
+	err = sem_chid_nolock(ns, sma, newid);
+
+	sem_unlock(sma);
+	up_write(&sem_ids(ns).rw_mutex);
+
+	/* ipc_chid may return -EAGAIN in case of memory requirement */
+	if (err == -EAGAIN)
+		goto retry;
+
+	return err;
+}
+
 static unsigned long copy_semid_to_user(void __user *buf, struct semid64_ds *in, int version)
 {
 	switch(version) {
Index: b/ipc/shm.c
===================================================================
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -162,7 +162,52 @@ static inline int shm_addid(struct ipc_n
 	return ipc_addid(&shm_ids(ns), &shp->shm_perm, ns->shm_ctlmni);
 }
 
+/* must be called with mutex and shp locks held */
+static long shm_chid_nolock(struct ipc_namespace *ns, struct shmid_kernel *shp,
+			    int newid)
+{
+	long err;
+
+	err = ipc_chid(&shm_ids(ns), shp->shm_perm.id, newid);
+	if (!err) {
+		shp->shm_file->f_dentry->d_inode->i_ino = newid;
+		shp->shm_ctim = get_seconds();
+	}
+
+	return err;
+}
+
+/* API to use for changing an id from kernel space, not from the syscall, as
+   there is no permission check done here */
+long shm_chid(struct ipc_namespace *ns, int id, int newid)
+{
+	long err;
+	struct shmid_kernel *shp;
+
+retry:
+	err = idr_pre_get(&shm_ids(ns).ipcs_idr, GFP_KERNEL);
+	if (!err)
+		return -ENOMEM;
+
+	down_write(&shm_ids(ns).rw_mutex);
+	shp = shm_lock_check(ns, id);
+
+	if (IS_ERR(shp)) {
+		up_write(&shm_ids(ns).rw_mutex);
+		return PTR_ERR(shp);
+	}
+
+	err = shm_chid_nolock(ns, shp, newid);
 
+	shm_unlock(shp);
+	up_write(&shm_ids(ns).rw_mutex);
+
+	/* ipc_chid may return -EAGAIN in case of memory requirement */
+	if (err == -EAGAIN)
+			goto retry;
+
+	return err;
+}
 
 /* This is called by fork, once for every shm attach. */
 static void shm_open(struct vm_area_struct *vma)
Index: b/ipc/util.c
===================================================================
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -363,6 +363,54 @@ retry:
 
 
 /**
+ *	ipc_chid 	-	change an IPC identifier
+ *	@ids: IPC identifier set
+ *	@oldid: ID of the IPC permission set to move
+ *	@newid: new ID of the IPC permission set to move
+ *
+ *	Move an entry in the IPC idr from the 'oldid' place to the
+ *      'newid' place. The seq number of the entry is updated to match the
+ *      'newid' value.
+ *
+ *	Called with the ipc lock and ipc_ids.rw_mutex held.
+ */
+int ipc_chid(struct ipc_ids *ids, int oldid, int newid)
+{
+	struct kern_ipc_perm *p;
+	int old_lid = oldid % SEQ_MULTIPLIER;
+	int new_lid = newid % SEQ_MULTIPLIER;
+
+	if (newid !=  (new_lid + (newid/SEQ_MULTIPLIER)*SEQ_MULTIPLIER))
+		return -EINVAL;
+
+	p = idr_find(&ids->ipcs_idr, old_lid);
+
+	if (!p)
+		return -EINVAL;
+
+	/* The idx in the idr may be the same but not the seq number. */
+	if (new_lid != old_lid) {
+		int id, err;
+
+		err = idr_get_new_above(&ids->ipcs_idr, p, new_lid, &id);
+		if (err)
+			return err;
+
+		/* do we get our wished id ? */
+		if (id == new_lid) {
+			idr_remove(&ids->ipcs_idr, old_lid);
+		} else {
+			idr_remove(&ids->ipcs_idr, id);
+			return -EBUSY;
+		}
+	}
+
+	p->id = newid;
+	p->seq = newid/SEQ_MULTIPLIER;
+	return 0;
+}
+
+/**
  *	ipc_rmid	-	remove an IPC identifier
  *	@ids: IPC identifier set
  *	@ipcp: ipc perm structure containing the identifier to remove
Index: b/ipc/util.h
===================================================================
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -85,6 +85,7 @@ int ipc_get_maxid(struct ipc_ids *);
 void ipc_rmid(struct ipc_ids *, struct kern_ipc_perm *);
 
 /* must be called with ipcp locked */
+int ipc_chid(struct ipc_ids *ids, int oldid, int newid);
 int ipcperms(struct kern_ipc_perm *ipcp, short flg);
 
 /* for rare, potentially huge allocations.

-- 
Pierre Peiffer