Viewing file:  namespace.c (27 KB) -rw-r--r--
Select action/file-type:
 (+) |  (+) |  (+) | Code (+) | Session (+) |  (+) | SDB (+) |  (+) |  (+) |  (+) |  (+) |  (+) |
/*
* linux/fs/namespace.c
*
* (C) Copyright Al Viro 2000, 2001
* Released under GPL v2.
*
* Based on code from fs/super.c, copyright Linus Torvalds and others.
* Heavily rewritten.
*/
#include <linux/config.h>
#include <linux/slab.h>
#include <linux/smp_lock.h>
#include <linux/init.h>
#include <linux/quotaops.h>
#include <linux/acct.h>
#include <linux/module.h>
#include <linux/devfs_fs_kernel.h>
#include <asm/uaccess.h>
#include <linux/seq_file.h>
struct vfsmount *do_kern_mount(char *type, int flags, char *name, void *data);
int do_remount_sb(struct super_block *sb, int flags, void * data);
void kill_super(struct super_block *sb);
static struct list_head *mount_hashtable;
static int hash_mask, hash_bits;
static kmem_cache_t *mnt_cache;
static LIST_HEAD(vfsmntlist);
static DECLARE_MUTEX(mount_sem);
/* Will be static */
struct vfsmount *root_vfsmnt;
static inline unsigned long hash(struct vfsmount *mnt, struct dentry *dentry)
{
unsigned long tmp = ((unsigned long) mnt / L1_CACHE_BYTES);
tmp += ((unsigned long) dentry / L1_CACHE_BYTES);
tmp = tmp + (tmp >> hash_bits);
return tmp & hash_mask;
}
struct vfsmount *alloc_vfsmnt(void)
{
struct vfsmount *mnt = kmem_cache_alloc(mnt_cache, GFP_KERNEL);
if (mnt) {
memset(mnt, 0, sizeof(struct vfsmount));
atomic_set(&mnt->mnt_count,1);
INIT_LIST_HEAD(&mnt->mnt_hash);
INIT_LIST_HEAD(&mnt->mnt_child);
INIT_LIST_HEAD(&mnt->mnt_mounts);
INIT_LIST_HEAD(&mnt->mnt_list);
}
return mnt;
}
void free_vfsmnt(struct vfsmount *mnt)
{
if (mnt->mnt_devname)
kfree(mnt->mnt_devname);
kmem_cache_free(mnt_cache, mnt);
}
void set_devname(struct vfsmount *mnt, const char *name)
{
if (name) {
int size = strlen(name)+1;
char * newname = kmalloc(size, GFP_KERNEL);
if (newname) {
memcpy(newname, name, size);
mnt->mnt_devname = newname;
}
}
}
struct vfsmount *lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)
{
struct list_head * head = mount_hashtable + hash(mnt, dentry);
struct list_head * tmp = head;
struct vfsmount *p;
for (;;) {
tmp = tmp->next;
p = NULL;
if (tmp == head)
break;
p = list_entry(tmp, struct vfsmount, mnt_hash);
if (p->mnt_parent == mnt && p->mnt_mountpoint == dentry)
break;
}
return p;
}
static int check_mnt(struct vfsmount *mnt)
{
spin_lock(&dcache_lock);
while (mnt->mnt_parent != mnt)
mnt = mnt->mnt_parent;
spin_unlock(&dcache_lock);
return mnt == root_vfsmnt;
}
static void detach_mnt(struct vfsmount *mnt, struct nameidata *old_nd)
{
old_nd->dentry = mnt->mnt_mountpoint;
old_nd->mnt = mnt->mnt_parent;
mnt->mnt_parent = mnt;
mnt->mnt_mountpoint = mnt->mnt_root;
list_del_init(&mnt->mnt_child);
list_del_init(&mnt->mnt_hash);
old_nd->dentry->d_mounted--;
}
static void attach_mnt(struct vfsmount *mnt, struct nameidata *nd)
{
mnt->mnt_parent = mntget(nd->mnt);
mnt->mnt_mountpoint = dget(nd->dentry);
list_add(&mnt->mnt_hash, mount_hashtable+hash(nd->mnt, nd->dentry));
list_add(&mnt->mnt_child, &nd->mnt->mnt_mounts);
nd->dentry->d_mounted++;
}
static struct vfsmount *next_mnt(struct vfsmount *p, struct vfsmount *root)
{
struct list_head *next = p->mnt_mounts.next;
if (next == &p->mnt_mounts) {
while (1) {
if (p == root)
return NULL;
next = p->mnt_child.next;
if (next != &p->mnt_parent->mnt_mounts)
break;
p = p->mnt_parent;
}
}
return list_entry(next, struct vfsmount, mnt_child);
}
static struct vfsmount *
clone_mnt(struct vfsmount *old, struct dentry *root)
{
struct super_block *sb = old->mnt_sb;
struct vfsmount *mnt = alloc_vfsmnt();
if (mnt) {
mnt->mnt_flags = old->mnt_flags;
set_devname(mnt, old->mnt_devname);
atomic_inc(&sb->s_active);
mnt->mnt_sb = sb;
mnt->mnt_root = dget(root);
mnt->mnt_mountpoint = mnt->mnt_root;
mnt->mnt_parent = mnt;
}
return mnt;
}
void __mntput(struct vfsmount *mnt)
{
struct super_block *sb = mnt->mnt_sb;
dput(mnt->mnt_root);
free_vfsmnt(mnt);
kill_super(sb);
}
/* iterator */
static void *m_start(struct seq_file *m, loff_t *pos)
{
struct list_head *p;
loff_t n = *pos;
down(&mount_sem);
list_for_each(p, &vfsmntlist)
if (!n--)
return list_entry(p, struct vfsmount, mnt_list);
return NULL;
}
static void *m_next(struct seq_file *m, void *v, loff_t *pos)
{
struct list_head *p = ((struct vfsmount *)v)->mnt_list.next;
(*pos)++;
return p==&vfsmntlist ? NULL : list_entry(p, struct vfsmount, mnt_list);
}
static void m_stop(struct seq_file *m, void *v)
{
up(&mount_sem);
}
static inline void mangle(struct seq_file *m, const char *s)
{
seq_escape(m, s, " \t\n\\");
}
static int show_vfsmnt(struct seq_file *m, void *v)
{
struct vfsmount *mnt = v;
int err = 0;
static struct proc_fs_info {
int flag;
char *str;
} fs_info[] = {
{ MS_SYNCHRONOUS, ",sync" },
{ MS_MANDLOCK, ",mand" },
{ MS_NOATIME, ",noatime" },
{ MS_NODIRATIME, ",nodiratime" },
{ 0, NULL }
};
static struct proc_fs_info mnt_info[] = {
{ MNT_NOSUID, ",nosuid" },
{ MNT_NODEV, ",nodev" },
{ MNT_NOEXEC, ",noexec" },
{ 0, NULL }
};
struct proc_fs_info *fs_infop;
char *path_buf, *path;
path_buf = (char *) __get_free_page(GFP_KERNEL);
if (!path_buf)
return -ENOMEM;
path = d_path(mnt->mnt_root, mnt, path_buf, PAGE_SIZE);
mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
seq_putc(m, ' ');
mangle(m, path);
free_page((unsigned long) path_buf);
seq_putc(m, ' ');
mangle(m, mnt->mnt_sb->s_type->name);
seq_puts(m, mnt->mnt_sb->s_flags & MS_RDONLY ? " ro" : " rw");
for (fs_infop = fs_info; fs_infop->flag; fs_infop++) {
if (mnt->mnt_sb->s_flags & fs_infop->flag)
seq_puts(m, fs_infop->str);
}
for (fs_infop = mnt_info; fs_infop->flag; fs_infop++) {
if (mnt->mnt_flags & fs_infop->flag)
seq_puts(m, fs_infop->str);
}
if (mnt->mnt_sb->s_op->show_options)
err = mnt->mnt_sb->s_op->show_options(m, mnt);
seq_puts(m, " 0 0\n");
return err;
}
struct seq_operations mounts_op = {
start: m_start,
next: m_next,
stop: m_stop,
show: show_vfsmnt
};
/*
* Doesn't take quota and stuff into account. IOW, in some cases it will
* give false negatives. The main reason why it's here is that we need
* a non-destructive way to look for easily umountable filesystems.
*/
int may_umount(struct vfsmount *mnt)
{
if (atomic_read(&mnt->mnt_count) > 2)
return -EBUSY;
return 0;
}
void umount_tree(struct vfsmount *mnt)
{
struct vfsmount *p;
LIST_HEAD(kill);
for (p = mnt; p; p = next_mnt(p, mnt)) {
list_del(&p->mnt_list);
list_add(&p->mnt_list, &kill);
}
while (!list_empty(&kill)) {
mnt = list_entry(kill.next, struct vfsmount, mnt_list);
list_del_init(&mnt->mnt_list);
if (mnt->mnt_parent == mnt) {
spin_unlock(&dcache_lock);
} else {
struct nameidata old_nd;
detach_mnt(mnt, &old_nd);
spin_unlock(&dcache_lock);
path_release(&old_nd);
}
mntput(mnt);
spin_lock(&dcache_lock);
}
}
static int do_umount(struct vfsmount *mnt, int flags)
{
struct super_block * sb = mnt->mnt_sb;
int retval = 0;
/*
* If we may have to abort operations to get out of this
* mount, and they will themselves hold resources we must
* allow the fs to do things. In the Unix tradition of
* 'Gee thats tricky lets do it in userspace' the umount_begin
* might fail to complete on the first run through as other tasks
* must return, and the like. Thats for the mount program to worry
* about for the moment.
*/
lock_kernel();
if( (flags&MNT_FORCE) && sb->s_op->umount_begin)
sb->s_op->umount_begin(sb);
unlock_kernel();
/*
* No sense to grab the lock for this test, but test itself looks
* somewhat bogus. Suggestions for better replacement?
* Ho-hum... In principle, we might treat that as umount + switch
* to rootfs. GC would eventually take care of the old vfsmount.
* Actually it makes sense, especially if rootfs would contain a
* /reboot - static binary that would close all descriptors and
* call reboot(9). Then init(8) could umount root and exec /reboot.
*/
if (mnt == current->fs->rootmnt && !(flags & MNT_DETACH)) {
/*
* Special case for "unmounting" root ...
* we just try to remount it readonly.
*/
down_write(&sb->s_umount);
if (!(sb->s_flags & MS_RDONLY)) {
lock_kernel();
retval = do_remount_sb(sb, MS_RDONLY, 0);
unlock_kernel();
}
up_write(&sb->s_umount);
return retval;
}
down(&mount_sem);
spin_lock(&dcache_lock);
if (atomic_read(&sb->s_active) == 1) {
/* last instance - try to be smart */
spin_unlock(&dcache_lock);
lock_kernel();
DQUOT_OFF(sb);
acct_auto_close(sb->s_dev);
unlock_kernel();
spin_lock(&dcache_lock);
}
retval = -EBUSY;
if (atomic_read(&mnt->mnt_count) == 2 || flags & MNT_DETACH) {
if (!list_empty(&mnt->mnt_list))
umount_tree(mnt);
retval = 0;
}
spin_unlock(&dcache_lock);
up(&mount_sem);
return retval;
}
/*
* Now umount can handle mount points as well as block devices.
* This is important for filesystems which use unnamed block devices.
*
* We now support a flag for forced unmount like the other 'big iron'
* unixes. Our API is identical to OSF/1 to avoid making a mess of AMD
*/
asmlinkage long sys_umount(char * name, int flags)
{
struct nameidata nd;
char *kname;
int retval;
kname = getname(name);
retval = PTR_ERR(kname);
if (IS_ERR(kname))
goto out;
retval = 0;
if (path_init(kname, LOOKUP_POSITIVE|LOOKUP_FOLLOW, &nd))
retval = path_walk(kname, &nd);
putname(kname);
if (retval)
goto out;
retval = -EINVAL;
if (nd.dentry != nd.mnt->mnt_root)
goto dput_and_out;
if (!check_mnt(nd.mnt))
goto dput_and_out;
retval = -EPERM;
if (!capable(CAP_SYS_ADMIN))
goto dput_and_out;
retval = do_umount(nd.mnt, flags);
dput_and_out:
path_release(&nd);
out:
return retval;
}
/*
* The 2.0 compatible umount. No flags.
*/
asmlinkage long sys_oldumount(char * name)
{
return sys_umount(name,0);
}
static int mount_is_safe(struct nameidata *nd)
{
if (capable(CAP_SYS_ADMIN))
return 0;
return -EPERM;
#ifdef notyet
if (S_ISLNK(nd->dentry->d_inode->i_mode))
return -EPERM;
if (nd->dentry->d_inode->i_mode & S_ISVTX) {
if (current->uid != nd->dentry->d_inode->i_uid)
return -EPERM;
}
if (permission(nd->dentry->d_inode, MAY_WRITE))
return -EPERM;
return 0;
#endif
}
static struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry)
{
struct vfsmount *p, *next, *q, *res;
struct nameidata nd;
p = mnt;
res = nd.mnt = q = clone_mnt(p, dentry);
if (!q)
goto Enomem;
q->mnt_parent = q;
q->mnt_mountpoint = p->mnt_mountpoint;
while ( (next = next_mnt(p, mnt)) != NULL) {
while (p != next->mnt_parent) {
p = p->mnt_parent;
q = q->mnt_parent;
}
p = next;
nd.mnt = q;
nd.dentry = p->mnt_mountpoint;
q = clone_mnt(p, p->mnt_root);
if (!q)
goto Enomem;
spin_lock(&dcache_lock);
list_add_tail(&q->mnt_list, &res->mnt_list);
attach_mnt(q, &nd);
spin_unlock(&dcache_lock);
}
return res;
Enomem:
if (res) {
spin_lock(&dcache_lock);
umount_tree(res);
spin_unlock(&dcache_lock);
}
return NULL;
}
/* Will become static */
int graft_tree(struct vfsmount *mnt, struct nameidata *nd)
{
int err;
if (mnt->mnt_sb->s_flags & MS_NOUSER)
return -EINVAL;
if (S_ISDIR(nd->dentry->d_inode->i_mode) !=
S_ISDIR(mnt->mnt_root->d_inode->i_mode))
return -ENOTDIR;
err = -ENOENT;
down(&nd->dentry->d_inode->i_zombie);
if (IS_DEADDIR(nd->dentry->d_inode))
goto out_unlock;
spin_lock(&dcache_lock);
if (IS_ROOT(nd->dentry) || !d_unhashed(nd->dentry)) {
struct list_head head;
attach_mnt(mnt, nd);
list_add_tail(&head, &mnt->mnt_list);
list_splice(&head, vfsmntlist.prev);
mntget(mnt);
err = 0;
}
spin_unlock(&dcache_lock);
out_unlock:
up(&nd->dentry->d_inode->i_zombie);
return err;
}
/*
* do loopback mount.
*/
static int do_loopback(struct nameidata *nd, char *old_name, int recurse)
{
struct nameidata old_nd;
struct vfsmount *mnt = NULL;
int err = mount_is_safe(nd);
if (err)
return err;
if (!old_name || !*old_name)
return -EINVAL;
if (path_init(old_name, LOOKUP_POSITIVE|LOOKUP_FOLLOW, &old_nd))
err = path_walk(old_name, &old_nd);
if (err)
return err;
down(&mount_sem);
err = -EINVAL;
if (check_mnt(nd->mnt) && (!recurse || check_mnt(old_nd.mnt))) {
err = -ENOMEM;
if (recurse)
mnt = copy_tree(old_nd.mnt, old_nd.dentry);
else
mnt = clone_mnt(old_nd.mnt, old_nd.dentry);
}
if (mnt) {
err = graft_tree(mnt, nd);
if (err) {
spin_lock(&dcache_lock);
umount_tree(mnt);
spin_unlock(&dcache_lock);
} else
mntput(mnt);
}
up(&mount_sem);
path_release(&old_nd);
return err;
}
/*
* change filesystem flags. dir should be a physical root of filesystem.
* If you've mounted a non-root directory somewhere and want to do remount
* on it - tough luck.
*/
static int do_remount(struct nameidata *nd,int flags,int mnt_flags,void *data)
{
int err;
struct super_block * sb = nd->mnt->mnt_sb;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
if (!check_mnt(nd->mnt))
return -EINVAL;
if (nd->dentry != nd->mnt->mnt_root)
return -EINVAL;
down_write(&sb->s_umount);
err = do_remount_sb(sb, flags, data);
if (!err)
nd->mnt->mnt_flags=mnt_flags;
up_write(&sb->s_umount);
return err;
}
static int do_move_mount(struct nameidata *nd, char *old_name)
{
struct nameidata old_nd, parent_nd;
struct vfsmount *p;
int err = 0;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
if (!old_name || !*old_name)
return -EINVAL;
if (path_init(old_name, LOOKUP_POSITIVE|LOOKUP_FOLLOW, &old_nd))
err = path_walk(old_name, &old_nd);
if (err)
return err;
down(&mount_sem);
while(d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry))
;
err = -EINVAL;
if (!check_mnt(nd->mnt) || !check_mnt(old_nd.mnt))
goto out;
err = -ENOENT;
down(&nd->dentry->d_inode->i_zombie);
if (IS_DEADDIR(nd->dentry->d_inode))
goto out1;
spin_lock(&dcache_lock);
if (!IS_ROOT(nd->dentry) && d_unhashed(nd->dentry))
goto out2;
err = -EINVAL;
if (old_nd.dentry != old_nd.mnt->mnt_root)
goto out2;
if (old_nd.mnt == old_nd.mnt->mnt_parent)
goto out2;
if (S_ISDIR(nd->dentry->d_inode->i_mode) !=
S_ISDIR(old_nd.dentry->d_inode->i_mode))
goto out2;
err = -ELOOP;
for (p = nd->mnt; p->mnt_parent!=p; p = p->mnt_parent)
if (p == old_nd.mnt)
goto out2;
err = 0;
detach_mnt(old_nd.mnt, &parent_nd);
attach_mnt(old_nd.mnt, nd);
out2:
spin_unlock(&dcache_lock);
out1:
up(&nd->dentry->d_inode->i_zombie);
out:
up(&mount_sem);
if (!err)
path_release(&parent_nd);
path_release(&old_nd);
return err;
}
static int do_add_mount(struct nameidata *nd, char *type, int flags,
int mnt_flags, char *name, void *data)
{
struct vfsmount *mnt = do_kern_mount(type, flags, name, data);
int err = PTR_ERR(mnt);
if (IS_ERR(mnt))
goto out;
down(&mount_sem);
/* Something was mounted here while we slept */
while(d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry))
;
err = -EINVAL;
if (!check_mnt(nd->mnt))
goto unlock;
/* Refuse the same filesystem on the same mount point */
err = -EBUSY;
if (nd->mnt->mnt_sb == mnt->mnt_sb && nd->mnt->mnt_root == nd->dentry)
goto unlock;
if (mnt->mnt_sb->s_op && mnt->mnt_sb->s_op->dmapi_mount_event) {
char *mntpt;
char *buf;
err = 0;
buf = (char *)__get_free_pages(GFP_KERNEL, 0);
if ( buf == NULL ){
printk("Failing mount of %s -- unable to allocate space for DMAPI mount event.\n", name );
err = -ENOMEM;
}
else {
mntpt = d_path(nd->dentry, nd->mnt, buf, PAGE_SIZE);
err = mnt->mnt_sb->s_op->dmapi_mount_event(mnt->mnt_sb, mntpt);
free_pages( (unsigned long)buf, 0 );
}
if (err)
goto unlock;
}
mnt->mnt_flags = mnt_flags;
err = graft_tree(mnt, nd);
unlock:
up(&mount_sem);
mntput(mnt);
out:
return err;
}
static int copy_mount_options (const void *data, unsigned long *where)
{
int i;
unsigned long page;
unsigned long size;
*where = 0;
if (!data)
return 0;
if (!(page = __get_free_page(GFP_KERNEL)))
return -ENOMEM;
/* We only care that *some* data at the address the user
* gave us is valid. Just in case, we'll zero
* the remainder of the page.
*/
/* copy_from_user cannot cross TASK_SIZE ! */
size = TASK_SIZE - (unsigned long)data;
if (size > PAGE_SIZE)
size = PAGE_SIZE;
i = size - copy_from_user((void *)page, data, size);
if (!i) {
free_page(page);
return -EFAULT;
}
if (i != PAGE_SIZE)
memset((char *)page + i, 0, PAGE_SIZE - i);
*where = page;
return 0;
}
/*
* Flags is a 32-bit value that allows up to 31 non-fs dependent flags to
* be given to the mount() call (ie: read-only, no-dev, no-suid etc).
*
* data is a (void *) that can point to any structure up to
* PAGE_SIZE-1 bytes, which can contain arbitrary fs-dependent
* information (or be NULL).
*
* Pre-0.97 versions of mount() didn't have a flags word.
* When the flags word was introduced its top half was required
* to have the magic value 0xC0ED, and this remained so until 2.4.0-test9.
* Therefore, if this magic number is present, it carries no information
* and must be discarded.
*/
long do_mount(char * dev_name, char * dir_name, char *type_page,
unsigned long flags, void *data_page)
{
struct nameidata nd;
int retval = 0;
int mnt_flags = 0;
/* Discard magic */
if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
flags &= ~MS_MGC_MSK;
/* Basic sanity checks */
if (!dir_name || !*dir_name || !memchr(dir_name, 0, PAGE_SIZE))
return -EINVAL;
if (dev_name && !memchr(dev_name, 0, PAGE_SIZE))
return -EINVAL;
/* Separate the per-mountpoint flags */
if (flags & MS_NOSUID)
mnt_flags |= MNT_NOSUID;
if (flags & MS_NODEV)
mnt_flags |= MNT_NODEV;
if (flags & MS_NOEXEC)
mnt_flags |= MNT_NOEXEC;
flags &= ~(MS_NOSUID|MS_NOEXEC|MS_NODEV);
/* ... and get the mountpoint */
if (path_init(dir_name, LOOKUP_FOLLOW|LOOKUP_POSITIVE, &nd))
retval = path_walk(dir_name, &nd);
if (retval)
return retval;
if (flags & MS_REMOUNT)
retval = do_remount(&nd, flags & ~MS_REMOUNT, mnt_flags,
data_page);
else if (flags & MS_BIND)
retval = do_loopback(&nd, dev_name, flags & MS_REC);
else if (flags & MS_MOVE)
retval = do_move_mount(&nd, dev_name);
else
retval = do_add_mount(&nd, type_page, flags, mnt_flags,
dev_name, data_page);
path_release(&nd);
return retval;
}
asmlinkage long sys_mount(char * dev_name, char * dir_name, char * type,
unsigned long flags, void * data)
{
int retval;
unsigned long data_page;
unsigned long type_page;
unsigned long dev_page;
char *dir_page;
retval = copy_mount_options (type, &type_page);
if (retval < 0)
return retval;
dir_page = getname(dir_name);
retval = PTR_ERR(dir_page);
if (IS_ERR(dir_page))
goto out1;
retval = copy_mount_options (dev_name, &dev_page);
if (retval < 0)
goto out2;
retval = copy_mount_options (data, &data_page);
if (retval < 0)
goto out3;
lock_kernel();
retval = do_mount((char*)dev_page, dir_page, (char*)type_page,
flags, (void*)data_page);
unlock_kernel();
free_page(data_page);
out3:
free_page(dev_page);
out2:
putname(dir_page);
out1:
free_page(type_page);
return retval;
}
static void chroot_fs_refs(struct nameidata *old_nd, struct nameidata *new_nd)
{
struct task_struct *p;
struct fs_struct *fs;
read_lock(&tasklist_lock);
for_each_task(p) {
task_lock(p);
fs = p->fs;
if (fs) {
atomic_inc(&fs->count);
task_unlock(p);
if (fs->root==old_nd->dentry&&fs->rootmnt==old_nd->mnt)
set_fs_root(fs, new_nd->mnt, new_nd->dentry);
if (fs->pwd==old_nd->dentry&&fs->pwdmnt==old_nd->mnt)
set_fs_pwd(fs, new_nd->mnt, new_nd->dentry);
put_fs_struct(fs);
} else
task_unlock(p);
}
read_unlock(&tasklist_lock);
}
/*
* Moves the current root to put_root, and sets root/cwd of all processes
* which had them on the old root to new_root.
*
* Note:
* - we don't move root/cwd if they are not at the root (reason: if something
* cared enough to change them, it's probably wrong to force them elsewhere)
* - it's okay to pick a root that isn't the root of a file system, e.g.
* /nfs/my_root where /nfs is the mount point. It must be a mountpoint,
* though, so you may need to say mount --bind /nfs/my_root /nfs/my_root
* first.
*/
asmlinkage long sys_pivot_root(const char *new_root, const char *put_old)
{
struct vfsmount *tmp;
struct nameidata new_nd, old_nd, parent_nd, root_parent, user_nd;
char *name;
int error;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
lock_kernel();
name = getname(new_root);
error = PTR_ERR(name);
if (IS_ERR(name))
goto out0;
error = 0;
if (path_init(name, LOOKUP_POSITIVE|LOOKUP_FOLLOW|LOOKUP_DIRECTORY, &new_nd))
error = path_walk(name, &new_nd);
putname(name);
if (error)
goto out0;
error = -EINVAL;
if (!check_mnt(new_nd.mnt))
goto out1;
name = getname(put_old);
error = PTR_ERR(name);
if (IS_ERR(name))
goto out1;
error = 0;
if (path_init(name, LOOKUP_POSITIVE|LOOKUP_FOLLOW|LOOKUP_DIRECTORY, &old_nd))
error = path_walk(name, &old_nd);
putname(name);
if (error)
goto out1;
read_lock(¤t->fs->lock);
user_nd.mnt = mntget(current->fs->rootmnt);
user_nd.dentry = dget(current->fs->root);
read_unlock(¤t->fs->lock);
down(&mount_sem);
down(&old_nd.dentry->d_inode->i_zombie);
error = -EINVAL;
if (!check_mnt(user_nd.mnt))
goto out2;
error = -ENOENT;
if (IS_DEADDIR(new_nd.dentry->d_inode))
goto out2;
if (d_unhashed(new_nd.dentry) && !IS_ROOT(new_nd.dentry))
goto out2;
if (d_unhashed(old_nd.dentry) && !IS_ROOT(old_nd.dentry))
goto out2;
error = -EBUSY;
if (new_nd.mnt == user_nd.mnt || old_nd.mnt == user_nd.mnt)
goto out2; /* loop */
error = -EINVAL;
if (user_nd.mnt->mnt_root != user_nd.dentry)
goto out2;
if (new_nd.mnt->mnt_root != new_nd.dentry)
goto out2; /* not a mountpoint */
tmp = old_nd.mnt; /* make sure we can reach put_old from new_root */
spin_lock(&dcache_lock);
if (tmp != new_nd.mnt) {
for (;;) {
if (tmp->mnt_parent == tmp)
goto out3;
if (tmp->mnt_parent == new_nd.mnt)
break;
tmp = tmp->mnt_parent;
}
if (!is_subdir(tmp->mnt_mountpoint, new_nd.dentry))
goto out3;
} else if (!is_subdir(old_nd.dentry, new_nd.dentry))
goto out3;
detach_mnt(new_nd.mnt, &parent_nd);
detach_mnt(user_nd.mnt, &root_parent);
attach_mnt(user_nd.mnt, &old_nd);
attach_mnt(new_nd.mnt, &root_parent);
spin_unlock(&dcache_lock);
chroot_fs_refs(&user_nd, &new_nd);
error = 0;
path_release(&root_parent);
path_release(&parent_nd);
out2:
up(&old_nd.dentry->d_inode->i_zombie);
up(&mount_sem);
path_release(&user_nd);
path_release(&old_nd);
out1:
path_release(&new_nd);
out0:
unlock_kernel();
return error;
out3:
spin_unlock(&dcache_lock);
goto out2;
}
/*
* Absolutely minimal fake fs - only empty root directory and nothing else.
* In 2.5 we'll use ramfs or tmpfs, but for now it's all we need - just
* something to go with root vfsmount.
*/
static struct dentry *rootfs_lookup(struct inode *dir, struct dentry *dentry)
{
d_add(dentry, NULL);
return NULL;
}
static struct file_operations rootfs_dir_operations = {
read: generic_read_dir,
readdir: dcache_readdir,
};
static struct inode_operations rootfs_dir_inode_operations = {
lookup: rootfs_lookup,
};
static struct super_block *rootfs_read_super(struct super_block * sb, void * data, int silent)
{
struct inode * inode;
struct dentry * root;
static struct super_operations s_ops = {};
sb->s_op = &s_ops;
inode = new_inode(sb);
if (!inode)
return NULL;
inode->i_mode = S_IFDIR|0555;
inode->i_uid = inode->i_gid = 0;
inode->i_op = &rootfs_dir_inode_operations;
inode->i_fop = &rootfs_dir_operations;
root = d_alloc_root(inode);
if (!root) {
iput(inode);
return NULL;
}
sb->s_root = root;
return sb;
}
static DECLARE_FSTYPE(root_fs_type, "rootfs", rootfs_read_super, FS_NOMOUNT);
static void __init init_mount_tree(void)
{
register_filesystem(&root_fs_type);
root_vfsmnt = do_kern_mount("rootfs", 0, "rootfs", NULL);
if (IS_ERR(root_vfsmnt))
panic("can't allocate root vfsmount");
}
void __init mnt_init(unsigned long mempages)
{
struct list_head *d;
unsigned long order;
unsigned int nr_hash;
int i;
mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct vfsmount),
0, SLAB_HWCACHE_ALIGN, NULL, NULL);
if (!mnt_cache)
panic("Cannot create vfsmount cache");
mempages >>= (16 - PAGE_SHIFT);
mempages *= sizeof(struct list_head);
for (order = 0; ((1UL << order) << PAGE_SHIFT) < mempages; order++)
;
do {
mount_hashtable = (struct list_head *)
__get_free_pages(GFP_ATOMIC, order);
} while (mount_hashtable == NULL && --order >= 0);
if (!mount_hashtable)
panic("Failed to allocate mount hash table\n");
/*
* Find the power-of-two list-heads that can fit into the allocation..
* We don't guarantee that "sizeof(struct list_head)" is necessarily
* a power-of-two.
*/
nr_hash = (1UL << order) * PAGE_SIZE / sizeof(struct list_head);
hash_bits = 0;
do {
hash_bits++;
} while ((nr_hash >> hash_bits) != 0);
hash_bits--;
/*
* Re-calculate the actual number of entries and the mask
* from the number of bits we can fit.
*/
nr_hash = 1UL << hash_bits;
hash_mask = nr_hash-1;
printk("Mount-cache hash table entries: %d (order: %ld, %ld bytes)\n",
nr_hash, order, (PAGE_SIZE << order));
/* And initialize the newly allocated array */
d = mount_hashtable;
i = nr_hash;
do {
INIT_LIST_HEAD(d);
d++;
i--;
} while (i);
init_mount_tree();
}
#ifdef CONFIG_BLK_DEV_INITRD
int __init change_root(kdev_t new_root_dev,const char *put_old)
{
struct vfsmount *old_rootmnt;
struct nameidata devfs_nd, nd;
struct nameidata parent_nd;
char *new_devname = kmalloc(strlen("/dev/root.old")+1, GFP_KERNEL);
int error = 0;
if (new_devname)
strcpy(new_devname, "/dev/root.old");
read_lock(¤t->fs->lock);
old_rootmnt = mntget(current->fs->rootmnt);
read_unlock(¤t->fs->lock);
/* First unmount devfs if mounted */
if (path_init("/dev", LOOKUP_FOLLOW|LOOKUP_POSITIVE, &devfs_nd))
error = path_walk("/dev", &devfs_nd);
if (!error) {
if (devfs_nd.mnt->mnt_sb->s_magic == DEVFS_SUPER_MAGIC &&
devfs_nd.dentry == devfs_nd.mnt->mnt_root) {
do_umount(devfs_nd.mnt, 0);
}
path_release(&devfs_nd);
}
spin_lock(&dcache_lock);
detach_mnt(old_rootmnt, &parent_nd);
spin_unlock(&dcache_lock);
ROOT_DEV = new_root_dev;
mount_root();
#if 1
shrink_dcache();
printk("change_root: old root has d_count=%d\n",
atomic_read(&old_rootmnt->mnt_root->d_count));
#endif
mount_devfs_fs ();
/*
* Get the new mount directory
*/
error = 0;
if (path_init(put_old, LOOKUP_FOLLOW|LOOKUP_POSITIVE|LOOKUP_DIRECTORY, &nd))
error = path_walk(put_old, &nd);
if (error) {
int blivet;
struct block_device *ramdisk = old_rootmnt->mnt_sb->s_bdev;
atomic_inc(&ramdisk->bd_count);
blivet = blkdev_get(ramdisk, FMODE_READ, 0, BDEV_FS);
printk(KERN_NOTICE "Trying to unmount old root ... ");
if (!blivet) {
spin_lock(&dcache_lock);
list_del_init(&old_rootmnt->mnt_list);
spin_unlock(&dcache_lock);
mntput(old_rootmnt);
mntput(old_rootmnt);
blivet = ioctl_by_bdev(ramdisk, BLKFLSBUF, 0);
path_release(&parent_nd);
blkdev_put(ramdisk, BDEV_FS);
}
if (blivet) {
printk(KERN_ERR "error %d\n", blivet);
} else {
printk("okay\n");
error = 0;
}
kfree(new_devname);
return error;
}
spin_lock(&dcache_lock);
attach_mnt(old_rootmnt, &nd);
if (new_devname) {
if (old_rootmnt->mnt_devname)
kfree(old_rootmnt->mnt_devname);
old_rootmnt->mnt_devname = new_devname;
}
spin_unlock(&dcache_lock);
/* put the old stuff */
path_release(&parent_nd);
mntput(old_rootmnt);
path_release(&nd);
return 0;
}
#endif
|