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>

1 files changed, 42 insertions, 1 deletions

diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index f120e120787..285b64a8b06 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;