[RFC][PATCH 4/8]: Per-mount allocated_ptys

[sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org]

From: Sukadev Bhattiprolu <sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
Subject: [RFC][PATCH 4/8]: Per-mount allocated_ptys

To enable multiple mounts of devpts, 'allocated_ptys' must be a per-mount
variable rather than a global variable.  Move 'allocated_ptys' into the
super_block's s_fs_info.

Changelog[v2]:
	Define and use DEVPTS_SB() wrapper.

---
 fs/devpts/inode.c |   58 +++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 51 insertions(+), 7 deletions(-)

Index: linux-2.6.26-rc8-mm1/fs/devpts/inode.c
===================================================================
--- linux-2.6.26-rc8-mm1.orig/fs/devpts/inode.c	2008-08-20 13:16:47.000000000 -0700
+++ linux-2.6.26-rc8-mm1/fs/devpts/inode.c	2008-08-20 13:19:17.000000000 -0700
@@ -29,7 +29,6 @@
 #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;
@@ -54,6 +53,15 @@ static match_table_t tokens = {
 	{Opt_err, NULL}
 };
 
+struct pts_fs_info {
+	struct idr allocated_ptys;
+};
+
+static inline struct pts_fs_info * DEVPTS_SB(struct super_block *sb)
+{
+	return sb->s_fs_info;
+}
+
 static inline struct super_block *pts_sb_from_inode(struct inode *inode)
 {
 	if (inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
@@ -125,6 +133,19 @@ static const struct super_operations dev
 	.show_options	= devpts_show_options,
 };
 
+static void *new_pts_fs_info(void)
+{
+	struct pts_fs_info *fsi;
+
+	fsi = kmalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
+	if (fsi) {
+		idr_init(&fsi->allocated_ptys);
+	}
+	printk(KERN_ERR "new_pts_fs_info(): Returning fsi %p\n", fsi);
+	return fsi;
+}
+
+
 static int
 devpts_fill_super(struct super_block *s, void *data, int silent)
 {
@@ -136,9 +157,13 @@ devpts_fill_super(struct super_block *s,
 	s->s_op = &devpts_sops;
 	s->s_time_gran = 1;
 
+	s->s_fs_info = new_pts_fs_info();
+	if (!s->s_fs_info)
+		goto fail;
+
 	inode = new_inode(s);
 	if (!inode)
-		goto fail;
+		goto free_fsi;
 	inode->i_ino = 1;
 	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 	inode->i_blocks = 0;
@@ -154,6 +179,9 @@ devpts_fill_super(struct super_block *s,
 	
 	printk("devpts: get root dentry failed\n");
 	iput(inode);
+
+free_fsi:
+	kfree(s->s_fs_info);
 fail:
 	return -ENOMEM;
 }
@@ -164,11 +192,22 @@ static int devpts_get_sb(struct file_sys
 	return get_sb_single(fs_type, flags, data, devpts_fill_super, mnt);
 }
 
+
+static void devpts_kill_sb(struct super_block *sb)
+{
+	struct pts_fs_info *fsi = DEVPTS_SB(sb);	// rcu ?
+
+	//idr_destroy(&fsi->allocated_ptys);
+	kfree(fsi);
+
+	kill_anon_super(sb);
+}
+
 static struct file_system_type devpts_fs_type = {
 	.owner		= THIS_MODULE,
 	.name		= "devpts",
 	.get_sb		= devpts_get_sb,
-	.kill_sb	= kill_anon_super,
+	.kill_sb	= devpts_kill_sb,
 };
 
 /*
@@ -187,14 +226,16 @@ int devpts_new_index(struct inode *inode
 {
 	int index;
 	int idr_ret;
+	struct super_block *sb = pts_sb_from_inode(inode);
+	struct pts_fs_info *fsi = DEVPTS_SB(sb); 	// need rcu ?
 
 retry:
-	if (!idr_pre_get(&allocated_ptys, GFP_KERNEL)) {
+	if (!idr_pre_get(&fsi->allocated_ptys, GFP_KERNEL)) {
 		return -ENOMEM;
 	}
 
 	mutex_lock(&allocated_ptys_lock);
-	idr_ret = idr_get_new(&allocated_ptys, NULL, &index);
+	idr_ret = idr_get_new(&fsi->allocated_ptys, NULL, &index);
 	if (idr_ret < 0) {
 		mutex_unlock(&allocated_ptys_lock);
 		if (idr_ret == -EAGAIN)
@@ -203,7 +244,7 @@ retry:
 	}
 
 	if (index >= pty_limit) {
-		idr_remove(&allocated_ptys, index);
+		idr_remove(&fsi->allocated_ptys, index);
 		mutex_unlock(&allocated_ptys_lock);
 		return -EIO;
 	}
@@ -213,8 +254,11 @@ retry:
 
 void devpts_kill_index(struct inode *inode, int idx)
 {
+	struct super_block *sb = pts_sb_from_inode(inode);
+	struct pts_fs_info *fsi = DEVPTS_SB(sb); 	// need rcu ?
+
 	mutex_lock(&allocated_ptys_lock);
-	idr_remove(&allocated_ptys, idx);
+	idr_remove(&fsi->allocated_ptys, idx);
 	mutex_unlock(&allocated_ptys_lock);
 }