linux/fs/devpts/inode.c
David Howells 454e2398be [PATCH] VFS: Permit filesystem to override root dentry on mount
Extend the get_sb() filesystem operation to take an extra argument that
permits the VFS to pass in the target vfsmount that defines the mountpoint.

The filesystem is then required to manually set the superblock and root dentry
pointers.  For most filesystems, this should be done with simple_set_mnt()
which will set the superblock pointer and then set the root dentry to the
superblock's s_root (as per the old default behaviour).

The get_sb() op now returns an integer as there's now no need to return the
superblock pointer.

This patch permits a superblock to be implicitly shared amongst several mount
points, such as can be done with NFS to avoid potential inode aliasing.  In
such a case, simple_set_mnt() would not be called, and instead the mnt_root
and mnt_sb would be set directly.

The patch also makes the following changes:

 (*) the get_sb_*() convenience functions in the core kernel now take a vfsmount
     pointer argument and return an integer, so most filesystems have to change
     very little.

 (*) If one of the convenience function is not used, then get_sb() should
     normally call simple_set_mnt() to instantiate the vfsmount. This will
     always return 0, and so can be tail-called from get_sb().

 (*) generic_shutdown_super() now calls shrink_dcache_sb() to clean up the
     dcache upon superblock destruction rather than shrink_dcache_anon().

     This is required because the superblock may now have multiple trees that
     aren't actually bound to s_root, but that still need to be cleaned up. The
     currently called functions assume that the whole tree is rooted at s_root,
     and that anonymous dentries are not the roots of trees which results in
     dentries being left unculled.

     However, with the way NFS superblock sharing are currently set to be
     implemented, these assumptions are violated: the root of the filesystem is
     simply a dummy dentry and inode (the real inode for '/' may well be
     inaccessible), and all the vfsmounts are rooted on anonymous[*] dentries
     with child trees.

     [*] Anonymous until discovered from another tree.

 (*) The documentation has been adjusted, including the additional bit of
     changing ext2_* into foo_* in the documentation.

[akpm@osdl.org: convert ipath_fs, do other stuff]
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: Nathan Scott <nathans@sgi.com>
Cc: Roland Dreier <rolandd@cisco.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-23 07:42:45 -07:00

243 lines
5.3 KiB
C

/* -*- linux-c -*- --------------------------------------------------------- *
*
* linux/fs/devpts/inode.c
*
* Copyright 1998-2004 H. Peter Anvin -- All Rights Reserved
*
* This file is part of the Linux kernel and is made available under
* the terms of the GNU General Public License, version 2, or at your
* option, any later version, incorporated herein by reference.
*
* ------------------------------------------------------------------------- */
#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/namei.h>
#include <linux/mount.h>
#include <linux/tty.h>
#include <linux/devpts_fs.h>
#include <linux/parser.h>
#define DEVPTS_SUPER_MAGIC 0x1cd1
static struct vfsmount *devpts_mnt;
static struct dentry *devpts_root;
static struct {
int setuid;
int setgid;
uid_t uid;
gid_t gid;
umode_t mode;
} config = {.mode = 0600};
enum {
Opt_uid, Opt_gid, Opt_mode,
Opt_err
};
static match_table_t tokens = {
{Opt_uid, "uid=%u"},
{Opt_gid, "gid=%u"},
{Opt_mode, "mode=%o"},
{Opt_err, NULL}
};
static int devpts_remount(struct super_block *sb, int *flags, char *data)
{
char *p;
config.setuid = 0;
config.setgid = 0;
config.uid = 0;
config.gid = 0;
config.mode = 0600;
while ((p = strsep(&data, ",")) != NULL) {
substring_t args[MAX_OPT_ARGS];
int token;
int option;
if (!*p)
continue;
token = match_token(p, tokens, args);
switch (token) {
case Opt_uid:
if (match_int(&args[0], &option))
return -EINVAL;
config.uid = option;
config.setuid = 1;
break;
case Opt_gid:
if (match_int(&args[0], &option))
return -EINVAL;
config.gid = option;
config.setgid = 1;
break;
case Opt_mode:
if (match_octal(&args[0], &option))
return -EINVAL;
config.mode = option & ~S_IFMT;
break;
default:
printk(KERN_ERR "devpts: called with bogus options\n");
return -EINVAL;
}
}
return 0;
}
static struct super_operations devpts_sops = {
.statfs = simple_statfs,
.remount_fs = devpts_remount,
};
static int
devpts_fill_super(struct super_block *s, void *data, int silent)
{
struct inode * inode;
s->s_blocksize = 1024;
s->s_blocksize_bits = 10;
s->s_magic = DEVPTS_SUPER_MAGIC;
s->s_op = &devpts_sops;
s->s_time_gran = 1;
inode = new_inode(s);
if (!inode)
goto fail;
inode->i_ino = 1;
inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
inode->i_blocks = 0;
inode->i_blksize = 1024;
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_fop = &simple_dir_operations;
inode->i_nlink = 2;
devpts_root = s->s_root = d_alloc_root(inode);
if (s->s_root)
return 0;
printk("devpts: get root dentry failed\n");
iput(inode);
fail:
return -ENOMEM;
}
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);
}
static struct file_system_type devpts_fs_type = {
.owner = THIS_MODULE,
.name = "devpts",
.get_sb = devpts_get_sb,
.kill_sb = kill_anon_super,
};
/*
* The normal naming convention is simply /dev/pts/<number>; this conforms
* to the System V naming convention
*/
static struct dentry *get_node(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));
}
int devpts_pty_new(struct tty_struct *tty)
{
int number = tty->index;
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);
/* 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);
if (!inode)
return -ENOMEM;
inode->i_ino = number+2;
inode->i_blksize = 1024;
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;
init_special_inode(inode, S_IFCHR|config.mode, device);
inode->u.generic_ip = tty;
dentry = get_node(number);
if (!IS_ERR(dentry) && !dentry->d_inode)
d_instantiate(dentry, inode);
mutex_unlock(&devpts_root->d_inode->i_mutex);
return 0;
}
struct tty_struct *devpts_get_tty(int number)
{
struct dentry *dentry = get_node(number);
struct tty_struct *tty;
tty = NULL;
if (!IS_ERR(dentry)) {
if (dentry->d_inode)
tty = dentry->d_inode->u.generic_ip;
dput(dentry);
}
mutex_unlock(&devpts_root->d_inode->i_mutex);
return tty;
}
void devpts_pty_kill(int number)
{
struct dentry *dentry = get_node(number);
if (!IS_ERR(dentry)) {
struct inode *inode = dentry->d_inode;
if (inode) {
inode->i_nlink--;
d_delete(dentry);
dput(dentry);
}
dput(dentry);
}
mutex_unlock(&devpts_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);
}
return err;
}
static void __exit exit_devpts_fs(void)
{
unregister_filesystem(&devpts_fs_type);
mntput(devpts_mnt);
}
module_init(init_devpts_fs)
module_exit(exit_devpts_fs)
MODULE_LICENSE("GPL");