[PATCH 3/4] devpts: Make the newinstance option historical
From: Eric W. Biederman
Date: Sat Sep 22 2012 - 23:50:44 EST
- Modify opening /dev/ptmx so that it opens /dev/pts/ptmx
As it appares nearly impossible to get udev to create a symlink
do this with a little sprinkle of in kernel magic.
- Cleanup the devpts mount code and only leave the code for
new instance.
Tested on debian and ubuntu without any problems.
Acked-by: "Serge E. Hallyn" <serge@xxxxxxxxxx>
Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
---
drivers/tty/pty.c | 4 +
fs/devpts/inode.c | 180 +++++++++++++++++----------------------------
include/linux/devpts_fs.h | 5 +
3 files changed, 77 insertions(+), 112 deletions(-)
diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index 6beb7e1..a605074 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -615,6 +615,10 @@ static int ptmx_open(struct inode *inode, struct file *filp)
int retval;
int index;
+ inode = devpts_redirect(filp);
+ if (IS_ERR(inode))
+ return PTR_ERR(inode);
+
nonseekable_open(inode, filp);
retval = tty_alloc_file(filp);
diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index 61b54aa..38136ae 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -25,6 +25,7 @@
#include <linux/parser.h>
#include <linux/fsnotify.h>
#include <linux/seq_file.h>
+#include <linux/file.h>
#define DEVPTS_DEFAULT_MODE 0600
@@ -94,7 +95,6 @@ struct pts_mount_opts {
kgid_t gid;
umode_t mode;
umode_t ptmxmode;
- int newinstance;
int max;
};
@@ -116,7 +116,6 @@ static const match_table_t tokens = {
struct pts_fs_info {
struct ida allocated_ptys;
struct pts_mount_opts mount_opts;
- struct dentry *ptmx_dentry;
};
static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
@@ -157,10 +156,6 @@ static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
opts->max = NR_UNIX98_PTY_MAX;
- /* newinstance makes sense only on initial mount */
- if (op == PARSE_MOUNT)
- opts->newinstance = 0;
-
while ((p = strsep(&data, ",")) != NULL) {
substring_t args[MAX_OPT_ARGS];
int token;
@@ -200,9 +195,7 @@ static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
opts->ptmxmode = option & S_IALLUGO;
break;
case Opt_newinstance:
- /* newinstance makes sense only on initial mount */
- if (op == PARSE_MOUNT)
- opts->newinstance = 1;
+ /* Historical */
break;
case Opt_max:
if (match_int(&args[0], &option) ||
@@ -229,14 +222,6 @@ static int mknod_ptmx(struct super_block *sb)
struct pts_fs_info *fsi = DEVPTS_SB(sb);
struct pts_mount_opts *opts = &fsi->mount_opts;
- mutex_lock(&root->d_inode->i_mutex);
-
- /* If we have already created ptmx node, return */
- if (fsi->ptmx_dentry) {
- rc = 0;
- goto out;
- }
-
dentry = d_alloc_name(root, "ptmx");
if (!dentry) {
printk(KERN_NOTICE "Unable to alloc dentry for ptmx node\n");
@@ -261,39 +246,17 @@ static int mknod_ptmx(struct super_block *sb)
d_add(dentry, inode);
- fsi->ptmx_dentry = dentry;
rc = 0;
out:
- mutex_unlock(&root->d_inode->i_mutex);
return rc;
}
-static void update_ptmx_mode(struct pts_fs_info *fsi)
-{
- struct inode *inode;
- if (fsi->ptmx_dentry) {
- inode = fsi->ptmx_dentry->d_inode;
- inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
- }
-}
-
static int devpts_remount(struct super_block *sb, int *flags, char *data)
{
- int err;
struct pts_fs_info *fsi = DEVPTS_SB(sb);
struct pts_mount_opts *opts = &fsi->mount_opts;
- err = parse_mount_options(data, PARSE_REMOUNT, opts);
-
- /*
- * parse_mount_options() restores options to default values
- * before parsing and may have changed ptmxmode. So, update the
- * mode in the inode too. Bogus options don't fail the remount,
- * so do this even on error return.
- */
- update_ptmx_mode(fsi);
-
- return err;
+ return parse_mount_options(data, PARSE_REMOUNT, opts);
}
static int devpts_show_options(struct seq_file *seq, struct dentry *root)
@@ -319,7 +282,7 @@ static const struct super_operations devpts_sops = {
.show_options = devpts_show_options,
};
-static void *new_pts_fs_info(void)
+static struct pts_fs_info *new_pts_fs_info(void)
{
struct pts_fs_info *fsi;
@@ -338,6 +301,8 @@ static int
devpts_fill_super(struct super_block *s, void *data, int silent)
{
struct inode *inode;
+ struct pts_fs_info *fsi;
+ int error = -ENOMEM;
s->s_blocksize = 1024;
s->s_blocksize_bits = 10;
@@ -345,13 +310,18 @@ devpts_fill_super(struct super_block *s, void *data, int silent)
s->s_op = &devpts_sops;
s->s_time_gran = 1;
- s->s_fs_info = new_pts_fs_info();
- if (!s->s_fs_info)
+ fsi = new_pts_fs_info();
+ s->s_fs_info = fsi;
+ if (!fsi)
goto fail;
+ error = parse_mount_options(data, PARSE_MOUNT, &fsi->mount_opts);
+ if (error)
+ goto fail_kfree;
+
inode = new_inode(s);
if (!inode)
- goto fail;
+ goto fail_kfree;
inode->i_ino = 1;
inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
@@ -360,87 +330,40 @@ devpts_fill_super(struct super_block *s, void *data, int silent)
set_nlink(inode, 2);
s->s_root = d_make_root(inode);
- if (s->s_root)
- return 0;
+ if (!s->s_root) {
+ printk(KERN_ERR "devpts: get root dentry failed\n");
+ goto fail_iput;
+ }
- printk(KERN_ERR "devpts: get root dentry failed\n");
+ error = mknod_ptmx(s);
+ if (error)
+ goto fail_put_root;
+
+ return 0;
+fail_put_root:
+ dput(s->s_root);
+ s->s_root = NULL;
+fail_iput:
+ iput(inode);
+fail_kfree:
+ kfree(fsi);
fail:
return -ENOMEM;
}
-static int compare_init_pts_sb(struct super_block *s, void *p)
-{
- if (devpts_mnt)
- return devpts_mnt->mnt_sb == s;
- return 0;
-}
/*
* devpts_mount()
*
- * If the '-o newinstance' mount option was specified, mount a new
- * (private) instance of devpts. PTYs created in this instance are
- * independent of the PTYs in other devpts instances.
- *
- * If the '-o newinstance' option was not specified, mount/remount the
- * initial kernel mount of devpts. This type of mount gives the
- * legacy, single-instance semantics.
- *
- * The 'newinstance' option is needed to support multiple namespace
- * semantics in devpts while preserving backward compatibility of the
- * current 'single-namespace' semantics. i.e all mounts of devpts
- * without the 'newinstance' mount option should bind to the initial
- * kernel mount, like mount_single().
- *
- * Mounts with 'newinstance' option create a new, private namespace.
+ * Mount a new (private) instance of devpts. PTYs created in this
+ * instance are independent of the PTYs in other devpts instances.
*
- * NOTE:
- *
- * For single-mount semantics, devpts cannot use mount_single(),
- * because mount_single()/sget() find and use the super-block from
- * the most recent mount of devpts. But that recent mount may be a
- * 'newinstance' mount and mount_single() would pick the newinstance
- * super-block instead of the initial super-block.
*/
static struct dentry *devpts_mount(struct file_system_type *fs_type,
int flags, const char *dev_name, void *data)
{
- int error;
- struct pts_mount_opts opts;
- struct super_block *s;
-
- error = parse_mount_options(data, PARSE_MOUNT, &opts);
- if (error)
- return ERR_PTR(error);
-
- if (opts.newinstance)
- s = sget(fs_type, NULL, set_anon_super, flags, NULL);
- else
- s = sget(fs_type, compare_init_pts_sb, set_anon_super, flags,
- NULL);
-
- if (IS_ERR(s))
- return ERR_CAST(s);
-
- if (!s->s_root) {
- error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
- if (error)
- goto out_undo_sget;
- s->s_flags |= MS_ACTIVE;
- }
-
- memcpy(&(DEVPTS_SB(s))->mount_opts, &opts, sizeof(opts));
-
- error = mknod_ptmx(s);
- if (error)
- goto out_undo_sget;
-
- return dget(s->s_root);
-
-out_undo_sget:
- deactivate_locked_super(s);
- return ERR_PTR(error);
+ return mount_nodev(fs_type, flags, data, devpts_fill_super);
}
static void devpts_kill_sb(struct super_block *sb)
@@ -457,6 +380,40 @@ static struct file_system_type devpts_fs_type = {
.kill_sb = devpts_kill_sb,
};
+struct inode *devpts_redirect(struct file *filp)
+{
+ struct inode *inode;
+ struct file *filp2;
+
+ /* Is the inode already a devpts inode? */
+ inode = filp->f_dentry->d_inode;
+ if (filp->f_dentry->d_sb->s_magic == DEVPTS_SUPER_MAGIC)
+ goto out;
+
+ /* Is f_dentry->d_parent usable? */
+ inode = ERR_PTR(-ENODEV);
+ if (filp->f_vfsmnt->mnt_root == filp->f_dentry)
+ goto out;
+
+ /* Is there a devpts inode we can use instead? */
+
+ filp2 = file_open_root(filp->f_dentry->d_parent, filp->f_vfsmnt,
+ "pts/ptmx", O_PATH);
+ if (!IS_ERR(filp2)) {
+ if (filp2->f_dentry->d_sb->s_magic == DEVPTS_SUPER_MAGIC) {
+ struct path old;
+ old = filp->f_path;
+ filp->f_path = filp2->f_path;
+ inode = filp->f_dentry->d_inode;
+ path_get(&filp->f_path);
+ path_put(&old);
+ }
+ fput(filp2);
+ }
+out:
+ return inode;
+}
+
/*
* The normal naming convention is simply /dev/pts/<number>; this conforms
* to the System V naming convention
@@ -474,8 +431,7 @@ retry:
return -ENOMEM;
mutex_lock(&allocated_ptys_lock);
- if (pty_count >= pty_limit -
- (fsi->mount_opts.newinstance ? pty_reserve : 0)) {
+ if (pty_count >= pty_limit - pty_reserve) {
mutex_unlock(&allocated_ptys_lock);
return -ENOSPC;
}
diff --git a/include/linux/devpts_fs.h b/include/linux/devpts_fs.h
index 2d539ae..fe2b41f 100644
--- a/include/linux/devpts_fs.h
+++ b/include/linux/devpts_fs.h
@@ -20,6 +20,7 @@
#ifdef CONFIG_UNIX98_PTYS
+struct inode *devpts_redirect(struct file *filp);
int devpts_new_index(struct inode *ptmx_inode);
void devpts_kill_index(struct inode *ptmx_inode, int idx);
/* mknod in devpts */
@@ -32,6 +33,10 @@ void devpts_pty_kill(struct tty_struct *tty);
#else
/* Dummy stubs in the no-pty case */
+static inline struct inode *devpts_redirect(struct file *filp)
+{
+ return ERR_PTR(-ENODEV);
+}
static inline int devpts_new_index(struct inode *ptmx_inode) { return -EINVAL; }
static inline void devpts_kill_index(struct inode *ptmx_inode, int idx) { }
static inline int devpts_pty_new(struct inode *ptmx_inode,
--
1.7.5.4
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