From: Sukadev Bhattiprolu <[EMAIL PROTECTED]>
Subject: [RFC][PATCH 4/6]: Allow mknod of ptmx in devpts
/dev/ptmx is closely tied to the devpts filesystem. An open of /dev/ptmx,
allocates the next pty index and the associated device shows up in the
devpts fs as /dev/pts/n.
Wih multiple mounts of devpts filesystem, an open of /dev/ptmx would be
unable to determine which instance of the devpts is being accessed.
One solution for this would be to create make /dev/ptmx a symlink to
/dev/pts/ptmx and create the device node, ptmx, in each instance of
devpts. When /dev/ptmx is opened, we can use the inode of /dev/pts/ptmx
to identify the specific devpts instance.
(This solution has an impact on the 'startup scripts', and that is
being discussed separately).
This patch merely enables creating the [c, 5:2] (ptmx) device in devpts
filesystem.
TODO:
- Ability to unlink the /dev/pts/ptmx
- Remove traces of '/dev/pts/tty' node
Changelog:
- Earlier version of this patch enabled creating /dev/pts/tty
as well. As pointed out by Al Viro and H. Peter Anvin, that
is not really necessary.
---
fs/devpts/inode.c | 56 +++++++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 53 insertions(+), 3 deletions(-)
Index: linux-2.6.26-rc8-mm1/fs/devpts/inode.c
===================================================================
--- linux-2.6.26-rc8-mm1.orig/fs/devpts/inode.c 2008-08-04 02:08:50.000000000
-0700
+++ linux-2.6.26-rc8-mm1/fs/devpts/inode.c 2008-08-04 17:26:26.000000000
-0700
@@ -141,6 +141,56 @@ static void *new_pts_fs_info(void)
}
+
+static int devpts_mknod(struct inode *dir, struct dentry *dentry,
+ int mode, dev_t rdev)
+{
+ int inum;
+ struct inode *inode;
+ struct super_block *sb = dir->i_sb;
+
+ if (dentry->d_inode)
+ return -EEXIST;
+
+ if (!S_ISCHR(mode))
+ return -EPERM;
+
+ if (rdev == MKDEV(TTYAUX_MAJOR, 2))
+ inum = 2;
+#if 0
+ else if (rdev == MKDEV(TTYAUX_MAJOR, 0))
+ inum = 3;
+#endif
+ else
+ return -EPERM;
+
+ inode = new_inode(sb);
+ if (!inode)
+ return -ENOMEM;
+
+ inode->i_ino = inum;
+ inode->i_uid = inode->i_gid = 0;
+ inode->i_blocks = 0;
+ inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
+
+ init_special_inode(inode, mode, rdev);
+
+ d_instantiate(dentry, inode);
+ /*
+ * Get a reference to the dentry so the device-nodes persist
+ * even when there are no active references to them. We use
+ * kill_litter_super() to remove this entry when unmounting
+ * devpts.
+ */
+ dget(dentry);
+ return 0;
+}
+
+const struct inode_operations devpts_dir_inode_operations = {
+ .lookup = simple_lookup,
+ .mknod = devpts_mknod,
+};
+
static int
devpts_fill_super(struct super_block *s, void *data, int silent)
{
@@ -164,7 +214,7 @@ devpts_fill_super(struct super_block *s,
inode->i_blocks = 0;
inode->i_uid = inode->i_gid = 0;
inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
- inode->i_op = &simple_dir_inode_operations;
+ inode->i_op = &devpts_dir_inode_operations;
inode->i_fop = &simple_dir_operations;
inode->i_nlink = 2;
@@ -195,7 +245,7 @@ static void devpts_kill_sb(struct super_
//idr_destroy(&fsi->allocated_ptys);
kfree(fsi);
- kill_anon_super(sb);
+ kill_litter_super(sb);
}
static struct file_system_type devpts_fs_type = {
@@ -274,7 +324,7 @@ int devpts_pty_new(struct inode *ptmx_in
if (!inode)
return -ENOMEM;
- inode->i_ino = number+2;
+ inode->i_ino = number+4;
inode->i_uid = config.setuid ? config.uid : current->fsuid;
inode->i_gid = config.setgid ? config.gid : current->fsgid;
inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
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