From: Sukadev Bhattiprolu <[EMAIL PROTECTED]>
Subject: [RFC][PATCH 3/4]: Enable multiple mounts of /dev/pts
To support multiple PTY namespaces, we should be allow multiple mounts of
/dev/pts, once within each PTY namespace.
This patch removes the get_sb_single() in devpts_get_sb() and uses test and
set sb interfaces to allow remounting /dev/pts. The patch also removes the
globals, 'devpts_root' and uses current_pts_mnt() to access 'devpts_mnt'
Changelog:
- Version 0: Based on earlier versions from Serge Hallyn and
Matt Helsley.
Signed-off-by: Sukadev Bhattiprolu <[EMAIL PROTECTED]>
---
fs/devpts/inode.c | 120 +++++++++++++++++++++++++++++++++++++++++++++---------
1 file changed, 101 insertions(+), 19 deletions(-)
Index: linux-2.6.24/fs/devpts/inode.c
===================================================================
--- linux-2.6.24.orig/fs/devpts/inode.c 2008-02-05 17:30:52.000000000 -0800
+++ linux-2.6.24/fs/devpts/inode.c 2008-02-05 19:16:39.000000000 -0800
@@ -34,7 +34,10 @@ static inline struct idr *current_pts_ns
}
static struct vfsmount *devpts_mnt;
-static struct dentry *devpts_root;
+static inline struct vfsmount *current_pts_ns_mnt(void)
+{
+ return devpts_mnt;
+}
static struct {
int setuid;
@@ -130,7 +133,7 @@ devpts_fill_super(struct super_block *s,
inode->i_fop = &simple_dir_operations;
inode->i_nlink = 2;
- devpts_root = s->s_root = d_alloc_root(inode);
+ s->s_root = d_alloc_root(inode);
if (s->s_root)
return 0;
@@ -140,10 +143,53 @@ fail:
return -ENOMEM;
}
+/*
+ * We use test and set super-block operations to help determine whether we
+ * need a new super-block for this namespace. get_sb() walks the list of
+ * existing devpts supers, comparing them with the @data ptr. Since we
+ * passed 'current's namespace as the @data pointer we can compare the
+ * namespace pointer in the super-block's 's_fs_info'. If the test is
+ * TRUE then get_sb() returns a new active reference to the super block.
+ * Otherwise, it helps us build an active reference to a new one.
+ */
+
+static int devpts_test_sb(struct super_block *sb, void *data)
+{
+ return sb->s_fs_info == data;
+}
+
+static int devpts_set_sb(struct super_block *sb, void *data)
+{
+ sb->s_fs_info = data;
+ return set_anon_super(sb, NULL);
+}
+
static int devpts_get_sb(struct file_system_type *fs_type,
int flags, const char *dev_name, void *data, struct vfsmount *mnt)
{
- return get_sb_single(fs_type, flags, data, devpts_fill_super, mnt);
+ struct super_block *sb;
+ int err;
+
+ /* hereafter we're very simlar to get_sb_nodev */
+ sb = sget(fs_type, devpts_test_sb, devpts_set_sb, data);
+ if (IS_ERR(sb))
+ return PTR_ERR(sb);
+
+ if (sb->s_root)
+ return simple_set_mnt(mnt, sb);
+
+ sb->s_flags = flags;
+ err = devpts_fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
+ if (err) {
+ up_write(&sb->s_umount);
+ deactivate_super(sb);
+ return err;
+ }
+
+ sb->s_flags |= MS_ACTIVE;
+ devpts_mnt = mnt;
+
+ return simple_set_mnt(mnt, sb);
}
static struct file_system_type devpts_fs_type = {
@@ -158,10 +204,9 @@ static struct file_system_type devpts_fs
* to the System V naming convention
*/
-static struct dentry *get_node(int num)
+static struct dentry *get_node(struct dentry *root, int num)
{
char s[12];
- struct dentry *root = devpts_root;
mutex_lock(&root->d_inode->i_mutex);
return lookup_one_len(s, root, sprintf(s, "%d", num));
}
@@ -207,12 +252,28 @@ int devpts_pty_new(struct tty_struct *tt
struct tty_driver *driver = tty->driver;
dev_t device = MKDEV(driver->major, driver->minor_start+number);
struct dentry *dentry;
- struct inode *inode = new_inode(devpts_mnt->mnt_sb);
+ struct dentry *root;
+ struct vfsmount *mnt;
+ struct inode *inode;
+
/* We're supposed to be given the slave end of a pty */
BUG_ON(driver->type != TTY_DRIVER_TYPE_PTY);
BUG_ON(driver->subtype != PTY_TYPE_SLAVE);
+ mnt = current_pts_ns_mnt();
+ if (!mnt)
+ return -ENOSYS;
+ root = mnt->mnt_root;
+
+ mutex_lock(&root->d_inode->i_mutex);
+ inode = idr_find(current_pts_ns_allocated_ptys(), number);
+ mutex_unlock(&root->d_inode->i_mutex);
+
+ if (inode && !IS_ERR(inode))
+ return -EEXIST;
+
+ inode = new_inode(mnt->mnt_sb);
if (!inode)
return -ENOMEM;
@@ -222,23 +283,31 @@ int devpts_pty_new(struct tty_struct *tt
inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
init_special_inode(inode, S_IFCHR|config.mode, device);
inode->i_private = tty;
+ idr_replace(current_pts_ns_allocated_ptys(), inode, number);
- dentry = get_node(number);
+ dentry = get_node(root, number);
if (!IS_ERR(dentry) && !dentry->d_inode) {
d_instantiate(dentry, inode);
- fsnotify_create(devpts_root->d_inode, dentry);
+ fsnotify_create(root->d_inode, dentry);
}
- mutex_unlock(&devpts_root->d_inode->i_mutex);
+ mutex_unlock(&root->d_inode->i_mutex);
return 0;
}
struct tty_struct *devpts_get_tty(int number)
{
- struct dentry *dentry = get_node(number);
+ struct vfsmount *mnt;
+ struct dentry *dentry;
struct tty_struct *tty;
+ mnt = current_pts_ns_mnt();
+ if (!mnt)
+ return NULL;
+
+ dentry = get_node(mnt->mnt_root, number);
+
tty = NULL;
if (!IS_ERR(dentry)) {
if (dentry->d_inode)
@@ -246,14 +315,21 @@ struct tty_struct *devpts_get_tty(int nu
dput(dentry);
}
- mutex_unlock(&devpts_root->d_inode->i_mutex);
+ mutex_unlock(&mnt->mnt_root->d_inode->i_mutex);
return tty;
}
void devpts_pty_kill(int number)
{
- struct dentry *dentry = get_node(number);
+ struct dentry *dentry;
+ struct dentry *root;
+ struct vfsmount *mnt;
+
+ mnt = current_pts_ns_mnt();
+ root = mnt->mnt_root;
+
+ dentry = get_node(root, number);
if (!IS_ERR(dentry)) {
struct inode *inode = dentry->d_inode;
@@ -264,17 +340,23 @@ void devpts_pty_kill(int number)
}
dput(dentry);
}
- mutex_unlock(&devpts_root->d_inode->i_mutex);
+ mutex_unlock(&root->d_inode->i_mutex);
}
static int __init init_devpts_fs(void)
{
- int err = register_filesystem(&devpts_fs_type);
- if (!err) {
- devpts_mnt = kern_mount(&devpts_fs_type);
- if (IS_ERR(devpts_mnt))
- err = PTR_ERR(devpts_mnt);
- }
+ struct vfsmount *mnt;
+ int err;
+
+ err = register_filesystem(&devpts_fs_type);
+ if (err)
+ return err;
+
+ mnt = kern_mount_data(&devpts_fs_type, NULL);
+ if (IS_ERR(mnt))
+ err = PTR_ERR(mnt);
+ else
+ devpts_mnt = mnt;
return err;
}
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