Messages in this thread Patch in this message |  | | Date | Tue, 8 Apr 2008 14:59:09 -0700 | From | sukadev@us ... | Subject | [RFC][PATCH 3/7]: Enable multiple mounts of /dev/pts |
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From: Sukadev Bhattiprolu <sukadev@us.ibm.com> Subject:[RFC][PATCH 3/7]: 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_mnt', 'devpts_root' and uses a skeletal 'init_pts_ns' to store the vfsmount.
Changelog [v3]: - Removed some unnecessary comments from devpts_set_sb()
Changelog [v2]:
- (Pavel Emelianov/Serge Hallyn) Remove reference to pts_ns from sb->s_fs_info to fix the circular reference (/dev/pts is not unmounted unless the pts_ns is destroyed, so we don't need a reference to the pts_ns).
Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com> Signed-off-by: Serge Hallyn <serue@us.ibm.com> Signed-off-by: Matt Helsley <matthltc@us.ibm.com> --- fs/devpts/inode.c | 151 +++++++++++++++++++++++++++++++++++++--------- include/linux/devpts_fs.h | 11 +++ 2 files changed, 134 insertions(+), 28 deletions(-)
Index: 2.6.25-rc5-mm1/include/linux/devpts_fs.h =================================================================== --- 2.6.25-rc5-mm1.orig/include/linux/devpts_fs.h 2008-03-24 20:04:26.000000000 -0700 +++ 2.6.25-rc5-mm1/include/linux/devpts_fs.h 2008-04-01 18:08:42.000000000 -0700 @@ -14,6 +14,17 @@ #define _LINUX_DEVPTS_FS_H #include <linux/errno.h> +#include <linux/nsproxy.h> +#include <linux/kref.h> +#include <linux/idr.h> + +struct pts_namespace { + struct kref kref; + struct idr allocated_ptys; + struct vfsmount *mnt; +}; + +extern struct pts_namespace init_pts_ns; #ifdef CONFIG_UNIX98_PTYS Index: 2.6.25-rc5-mm1/fs/devpts/inode.c =================================================================== --- 2.6.25-rc5-mm1.orig/fs/devpts/inode.c 2008-03-24 20:04:26.000000000 -0700 +++ 2.6.25-rc5-mm1/fs/devpts/inode.c 2008-04-01 18:08:41.000000000 -0700 @@ -28,12 +28,8 @@ #define DEVPTS_DEFAULT_MODE 0600 extern int pty_limit; /* Config limit on Unix98 ptys */ -static DEFINE_IDR(allocated_ptys); static DECLARE_MUTEX(allocated_ptys_lock); -static struct vfsmount *devpts_mnt; -static struct dentry *devpts_root; - static struct { int setuid; int setgid; @@ -54,6 +50,15 @@ static match_table_t tokens = { {Opt_err, NULL} }; +struct pts_namespace init_pts_ns = { + .kref = { + .refcount = ATOMIC_INIT(2), + }, + .allocated_ptys = IDR_INIT(init_pts_ns.allocated_ptys), + .mnt = NULL, +}; + + static int devpts_remount(struct super_block *sb, int *flags, char *data) { char *p; @@ -140,7 +145,7 @@ 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; @@ -150,17 +155,73 @@ 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; + struct pts_namespace *ns; + int err; + + /* hereafter we're very similar to proc_get_sb */ + if (flags & MS_KERNMOUNT) + ns = data; + else + ns = &init_pts_ns; + + /* hereafter we're very simlar to get_sb_nodev */ + sb = sget(fs_type, devpts_test_sb, devpts_set_sb, ns); + 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; + ns->mnt = mnt; + + return simple_set_mnt(mnt, sb); +} + +static void devpts_kill_sb(struct super_block *sb) +{ + sb->s_fs_info = NULL; + 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, }; /* @@ -168,10 +229,9 @@ 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)); } @@ -180,14 +240,15 @@ int devpts_new_index(void) { int index; int idr_ret; + struct pts_namespace *pts_ns = &init_pts_ns; retry: - if (!idr_pre_get(&allocated_ptys, GFP_KERNEL)) { + if (!idr_pre_get(&pts_ns->allocated_ptys, GFP_KERNEL)) { return -ENOMEM; } down(&allocated_ptys_lock); - idr_ret = idr_get_new(&allocated_ptys, NULL, &index); + idr_ret = idr_get_new(&pts_ns->allocated_ptys, NULL, &index); if (idr_ret < 0) { up(&allocated_ptys_lock); if (idr_ret == -EAGAIN) @@ -196,7 +257,7 @@ retry: } if (index >= pty_limit) { - idr_remove(&allocated_ptys, index); + idr_remove(&pts_ns->allocated_ptys, index); up(&allocated_ptys_lock); return -EIO; } @@ -206,8 +267,10 @@ retry: void devpts_kill_index(int idx) { + struct pts_namespace *pts_ns = &init_pts_ns; + down(&allocated_ptys_lock); - idr_remove(&allocated_ptys, idx); + idr_remove(&pts_ns->allocated_ptys, idx); up(&allocated_ptys_lock); } @@ -217,12 +280,26 @@ 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; + struct pts_namespace *pts_ns = &init_pts_ns; /* 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 = pts_ns->mnt; + root = mnt->mnt_root; + + mutex_lock(&root->d_inode->i_mutex); + inode = idr_find(&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; @@ -232,23 +309,29 @@ 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(&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 = init_pts_ns.mnt; + + dentry = get_node(mnt->mnt_root, number); + tty = NULL; if (!IS_ERR(dentry)) { if (dentry->d_inode) @@ -256,14 +339,19 @@ 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; + + root = init_pts_ns.mnt->mnt_root; + + dentry = get_node(root, number); if (!IS_ERR(dentry)) { struct inode *inode = dentry->d_inode; @@ -274,24 +362,31 @@ 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, &init_pts_ns); + if (IS_ERR(mnt)) + err = PTR_ERR(mnt); + else + init_pts_ns.mnt = mnt; return err; } static void __exit exit_devpts_fs(void) { unregister_filesystem(&devpts_fs_type); - mntput(devpts_mnt); + mntput(init_pts_ns.mnt); + init_pts_ns.mnt = NULL; } module_init(init_devpts_fs)
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