[Devel] [RFC PATCH 2/5] use next syscall data to predefine ipc objects ids

[Nadia.Derbey at bull.net]

[PATCH 02/05]

This patch uses the value written into the next_syscall_data proc file
as a target id for the next IPC object to be created.
The following syscalls have a new behavior if next_syscall_data is set:
. mssget()
. semget()
. shmget()

Signed-off-by: Nadia Derbey <Nadia.Derbey at bull.net>

---
 include/linux/next_syscall_data.h |   17 ++++++++++++++--
 ipc/util.c                        |   39 ++++++++++++++++++++++++++++++--------
 2 files changed, 46 insertions(+), 10 deletions(-)

Index: linux-2.6.26-rc8-mm1/include/linux/next_syscall_data.h
===================================================================
--- linux-2.6.26-rc8-mm1.orig/include/linux/next_syscall_data.h	2008-07-08 09:24:38.000000000 +0200
+++ linux-2.6.26-rc8-mm1/include/linux/next_syscall_data.h	2008-07-08 12:12:39.000000000 +0200
@@ -1,7 +1,10 @@
 /*
  * include/linux/next_syscall_data.h
  *
- * Definitions to support fixed data for next syscall to be called.
+ * Definitions to support fixed data for next syscall to be called. The
+ * following is supported today:
+ *    . object creation with a predefined id
+ *         . for a sysv ipc object
  */
 
 #ifndef _LINUX_NEXT_SYSCALL_DATA_H
@@ -13,13 +16,23 @@
  * If this structure is pointed to by a task_struct, next syscall to be called
  * by the task will have a non-default behavior.
  * For example, it can be used to pre-set the id of the object to be created
- * by next syscall.
+ * by next syscall. The following syscalls support this feature:
+ *    . msgget(), semget(), shmget()
  */
 struct next_syscall_data {
 	int ndata;
 	long data[NDATA];
 };
 
+/*
+ * Returns true if tsk has some data set in its next_syscall_data, 0 else
+ */
+#define next_data_set(tsk)	((tsk)->nsd				\
+					? ((tsk)->nsd->ndata ? 1 : 0)	\
+					: 0)
+
+#define get_next_data(tsk)	((tsk)->nsd->data[0])
+
 extern ssize_t get_next_syscall_data(struct task_struct *, char *, size_t);
 extern int set_next_syscall_data(struct task_struct *, char *);
 extern void reset_next_syscall_data(struct task_struct *);
Index: linux-2.6.26-rc8-mm1/ipc/util.c
===================================================================
--- linux-2.6.26-rc8-mm1.orig/ipc/util.c	2008-07-08 09:05:09.000000000 +0200
+++ linux-2.6.26-rc8-mm1/ipc/util.c	2008-07-08 12:13:40.000000000 +0200
@@ -266,20 +266,43 @@ int ipc_addid(struct ipc_ids* ids, struc
 	if (ids->in_use >= size)
 		return -ENOSPC;
 
-	err = idr_get_new(&ids->ipcs_idr, new, &id);
-	if (err)
-		return err;
+	if (unlikely(next_data_set(current))) {
+		/* There is a target id specified, try to use it */
+		int next_id = get_next_data(current);
+		int new_lid = next_id % SEQ_MULTIPLIER;
+		unsigned long new_seq = next_id / SEQ_MULTIPLIER;
+
+		reset_next_syscall_data(current);
+
+		if (next_id != (new_lid + (new_seq * SEQ_MULTIPLIER)))
+			return -EINVAL;
+
+		err = idr_get_new_above(&ids->ipcs_idr, new, new_lid, &id);
+		if (err)
+			return err;
+		if (id != new_lid) {
+			idr_remove(&ids->ipcs_idr, id);
+			return -EBUSY;
+		}
+
+		new->id = next_id;
+		new->seq = new_seq;
+	} else {
+		err = idr_get_new(&ids->ipcs_idr, new, &id);
+		if (err)
+			return err;
+
+		new->seq = ids->seq++;
+		if (ids->seq > ids->seq_max)
+			ids->seq = 0;
+		new->id = ipc_buildid(id, new->seq);
+	}
 
 	ids->in_use++;
 
 	new->cuid = new->uid = current->euid;
 	new->gid = new->cgid = current->egid;
 
-	new->seq = ids->seq++;
-	if(ids->seq > ids->seq_max)
-		ids->seq = 0;
-
-	new->id = ipc_buildid(id, new->seq);
 	spin_lock_init(&new->lock);
 	new->deleted = 0;
 	rcu_read_lock();

--
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