devpts: factor out PTY index allocation

Factor out the code used to allocate/free a pts index into new interfaces,
devpts_new_index() and devpts_kill_index().  This localizes the external data
structures used in managing the pts indices.

[akpm@linux-foundation.org: undo accidental mutex2sem conversion]
Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Signed-off-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Matt Helsley <matthltc@us.ibm.com>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 52 insertions, 35 deletions

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index edcb7e471f02..1d298c2cf930 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -91,7 +91,6 @@
 #include <linux/module.h>
 #include <linux/smp_lock.h>
 #include <linux/device.h>
-#include <linux/idr.h>
 #include <linux/wait.h>
 #include <linux/bitops.h>
 #include <linux/delay.h>
@@ -137,9 +136,6 @@ EXPORT_SYMBOL(tty_mutex);
 
 #ifdef CONFIG_UNIX98_PTYS
 extern struct tty_driver *ptm_driver;   /* Unix98 pty masters; for /dev/ptmx */
-extern int pty_limit;                   /* Config limit on Unix98 ptys */
-static DEFINE_IDR(allocated_ptys);
-static DEFINE_MUTEX(allocated_ptys_lock);
 static int ptmx_open(struct inode *, struct file *);
 #endif
 
@@ -2639,15 +2635,9 @@ static void release_dev(struct file *filp)
          */
         release_tty(tty, idx);
 
-#ifdef CONFIG_UNIX98_PTYS
         /* Make this pty number available for reallocation */
-        if (devpts) {
-                mutex_lock(&allocated_ptys_lock);
-                idr_remove(&allocated_ptys, idx);
-                mutex_unlock(&allocated_ptys_lock);
-        }
-#endif
-
+        if (devpts)
+                devpts_kill_index(idx);
 }
 
 /**
@@ -2803,29 +2793,13 @@ static int ptmx_open(struct inode *inode, struct file *filp)
         struct tty_struct *tty;
         int retval;
         int index;
-        int idr_ret;
 
         nonseekable_open(inode, filp);
 
         /* find a device that is not in use. */
-        mutex_lock(&allocated_ptys_lock);
-        if (!idr_pre_get(&allocated_ptys, GFP_KERNEL)) {
-                mutex_unlock(&allocated_ptys_lock);
-                return -ENOMEM;
-        }
-        idr_ret = idr_get_new(&allocated_ptys, NULL, &index);
-        if (idr_ret < 0) {
-                mutex_unlock(&allocated_ptys_lock);
-                if (idr_ret == -EAGAIN)
-                        return -ENOMEM;
-                return -EIO;
-        }
-        if (index >= pty_limit) {
-                idr_remove(&allocated_ptys, index);
-                mutex_unlock(&allocated_ptys_lock);
-                return -EIO;
-        }
-        mutex_unlock(&allocated_ptys_lock);
+        index = devpts_new_index();
+        if (index < 0)
+                return index;
 
         mutex_lock(&tty_mutex);
         retval = init_dev(ptm_driver, index, &tty);
@@ -2850,9 +2824,7 @@ out1:
         release_dev(filp);
         return retval;
 out:
-        mutex_lock(&allocated_ptys_lock);
-        idr_remove(&allocated_ptys, index);
-        mutex_unlock(&allocated_ptys_lock);
+        devpts_kill_index(index);
         return retval;
 }
 #endif
diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index f120e1207874..285b64a8b06e 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -17,6 +17,8 @@
 #include <linux/namei.h>
 #include <linux/mount.h>
 #include <linux/tty.h>
+#include <linux/mutex.h>
+#include <linux/idr.h>
 #include <linux/devpts_fs.h>
 #include <linux/parser.h>
 #include <linux/fsnotify.h>
@@ -26,6 +28,10 @@
 
 #define DEVPTS_DEFAULT_MODE 0600
 
+extern int pty_limit;                   /* Config limit on Unix98 ptys */
+static DEFINE_IDR(allocated_ptys);
+static DEFINE_MUTEX(allocated_ptys_lock);
+
 static struct vfsmount *devpts_mnt;
 static struct dentry *devpts_root;
 
@@ -171,9 +177,44 @@ static struct dentry *get_node(int num)
         return lookup_one_len(s, root, sprintf(s, "%d", num));
 }
 
+int devpts_new_index(void)
+{
+        int index;
+        int idr_ret;
+
+retry:
+        if (!idr_pre_get(&allocated_ptys, GFP_KERNEL)) {
+                return -ENOMEM;
+        }
+
+        mutex_lock(&allocated_ptys_lock);
+        idr_ret = idr_get_new(&allocated_ptys, NULL, &index);
+        if (idr_ret < 0) {
+                mutex_unlock(&allocated_ptys_lock);
+                if (idr_ret == -EAGAIN)
+                        goto retry;
+                return -EIO;
+        }
+
+        if (index >= pty_limit) {
+                idr_remove(&allocated_ptys, index);
+                mutex_unlock(&allocated_ptys_lock);
+                return -EIO;
+        }
+        mutex_unlock(&allocated_ptys_lock);
+        return index;
+}
+
+void devpts_kill_index(int idx)
+{
+        mutex_lock(&allocated_ptys_lock);
+        idr_remove(&allocated_ptys, idx);
+        mutex_unlock(&allocated_ptys_lock);
+}
+
 int devpts_pty_new(struct tty_struct *tty)
 {
-        int number = tty->index;
+        int number = tty->index; /* tty layer puts index from devpts_new_index() in here */
         struct tty_driver *driver = tty->driver;
         dev_t device = MKDEV(driver->major, driver->minor_start+number);
         struct dentry *dentry;
diff --git a/include/linux/devpts_fs.h b/include/linux/devpts_fs.h
index b672ddc00735..154769cad3f3 100644
--- a/include/linux/devpts_fs.h
+++ b/include/linux/devpts_fs.h
@@ -17,6 +17,8 @@
 
 #ifdef CONFIG_UNIX98_PTYS
 
+int devpts_new_index(void);
+void devpts_kill_index(int idx);
 int devpts_pty_new(struct tty_struct *tty);      /* mknod in devpts */
 struct tty_struct *devpts_get_tty(int number);   /* get tty structure */
 void devpts_pty_kill(int number);                /* unlink */
@@ -24,6 +26,8 @@ void devpts_pty_kill(int number);		 /* unlink */
 #else
 
 /* Dummy stubs in the no-pty case */
+static inline int devpts_new_index(void) { return -EINVAL; }
+static inline void devpts_kill_index(int idx) { }
 static inline int devpts_pty_new(struct tty_struct *tty) { return -EINVAL; }
 static inline struct tty_struct *devpts_get_tty(int number) { return NULL; }
 static inline void devpts_pty_kill(int number) { }