patch-2.4.11-dontuse linux/fs/namespace.c

Next file: linux/fs/ncpfs/inode.c
Previous file: linux/fs/namei.c
Back to the patch index
Back to the overall index

diff -u --recursive --new-file v2.4.10/linux/fs/namespace.c linux/fs/namespace.c
@@ -0,0 +1,1124 @@
+/*
+ *  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/nfs_fs.h>
+#include <linux/nfs_fs_sb.h>
+#include <linux/nfs_mount.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);
+	}
+	return mnt;
+}
+
+void __mntput(struct vfsmount *mnt)
+{
+	struct super_block *sb = mnt->mnt_sb;
+	dput(mnt->mnt_root);
+	free_vfsmnt(mnt);
+	kill_super(sb);
+}
+
+/* Use octal escapes, like mount does, for embedded spaces etc. */
+static unsigned char need_escaping[] = { ' ', '\t', '\n', '\\' };
+
+static int
+mangle(const unsigned char *s, char *buf, int len) {
+        char *sp;
+        int n;
+
+        sp = buf;
+        while(*s && sp-buf < len-3) {
+                for (n = 0; n < sizeof(need_escaping); n++) {
+                        if (*s == need_escaping[n]) {
+                                *sp++ = '\\';
+                                *sp++ = '0' + ((*s & 0300) >> 6);
+                                *sp++ = '0' + ((*s & 070) >> 3);
+                                *sp++ = '0' + (*s & 07);
+                                goto next;
+                        }
+                }
+                *sp++ = *s;
+        next:
+                s++;
+        }
+        return sp - buf;	/* no trailing NUL */
+}
+
+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 }
+};
+
+static struct proc_nfs_info {
+	int flag;
+	char *str;
+	char *nostr;
+} nfs_info[] = {
+	{ NFS_MOUNT_SOFT, ",soft", ",hard" },
+	{ NFS_MOUNT_INTR, ",intr", "" },
+	{ NFS_MOUNT_POSIX, ",posix", "" },
+	{ NFS_MOUNT_TCP, ",tcp", ",udp" },
+	{ NFS_MOUNT_NOCTO, ",nocto", "" },
+	{ NFS_MOUNT_NOAC, ",noac", "" },
+	{ NFS_MOUNT_NONLM, ",nolock", ",lock" },
+	{ NFS_MOUNT_BROKEN_SUID, ",broken_suid", "" },
+	{ 0, NULL, NULL }
+};
+
+int get_filesystem_info( char *buf )
+{
+	struct list_head *p;
+	struct proc_fs_info *fs_infop;
+	struct proc_nfs_info *nfs_infop;
+	struct nfs_server *nfss;
+	int len, prevlen;
+	char *path, *buffer = (char *) __get_free_page(GFP_KERNEL);
+
+	if (!buffer) return 0;
+	len = prevlen = 0;
+
+#define FREEROOM	((int)PAGE_SIZE-200-len)
+#define MANGLE(s)	len += mangle((s), buf+len, FREEROOM);
+
+	for (p = vfsmntlist.next; p != &vfsmntlist; p = p->next) {
+		struct vfsmount *tmp = list_entry(p, struct vfsmount, mnt_list);
+		path = d_path(tmp->mnt_root, tmp, buffer, PAGE_SIZE);
+		if (!path)
+			continue;
+		MANGLE(tmp->mnt_devname ? tmp->mnt_devname : "none");
+		buf[len++] = ' ';
+		MANGLE(path);
+		buf[len++] = ' ';
+		MANGLE(tmp->mnt_sb->s_type->name);
+		len += sprintf(buf+len, " %s",
+			       tmp->mnt_sb->s_flags & MS_RDONLY ? "ro" : "rw");
+		for (fs_infop = fs_info; fs_infop->flag; fs_infop++) {
+			if (tmp->mnt_sb->s_flags & fs_infop->flag)
+				MANGLE(fs_infop->str);
+		}
+		for (fs_infop = mnt_info; fs_infop->flag; fs_infop++) {
+			if (tmp->mnt_flags & fs_infop->flag)
+				MANGLE(fs_infop->str);
+		}
+		if (!strcmp("nfs", tmp->mnt_sb->s_type->name)) {
+			nfss = &tmp->mnt_sb->u.nfs_sb.s_server;
+			len += sprintf(buf+len, ",v%d", nfss->rpc_ops->version);
+
+			len += sprintf(buf+len, ",rsize=%d", nfss->rsize);
+
+			len += sprintf(buf+len, ",wsize=%d", nfss->wsize);
+#if 0
+			if (nfss->timeo != 7*HZ/10) {
+				len += sprintf(buf+len, ",timeo=%d",
+					       nfss->timeo*10/HZ);
+			}
+			if (nfss->retrans != 3) {
+				len += sprintf(buf+len, ",retrans=%d",
+					       nfss->retrans);
+			}
+#endif
+			if (nfss->acregmin != 3*HZ) {
+				len += sprintf(buf+len, ",acregmin=%d",
+					       nfss->acregmin/HZ);
+			}
+			if (nfss->acregmax != 60*HZ) {
+				len += sprintf(buf+len, ",acregmax=%d",
+					       nfss->acregmax/HZ);
+			}
+			if (nfss->acdirmin != 30*HZ) {
+				len += sprintf(buf+len, ",acdirmin=%d",
+					       nfss->acdirmin/HZ);
+			}
+			if (nfss->acdirmax != 60*HZ) {
+				len += sprintf(buf+len, ",acdirmax=%d",
+					       nfss->acdirmax/HZ);
+			}
+			for (nfs_infop = nfs_info; nfs_infop->flag; nfs_infop++) {
+				char *str;
+				if (nfss->flags & nfs_infop->flag)
+					str = nfs_infop->str;
+				else
+					str = nfs_infop->nostr;
+				MANGLE(str);
+			}
+			len += sprintf(buf+len, ",addr=");
+			MANGLE(nfss->hostname);
+		}
+		len += sprintf(buf + len, " 0 0\n");
+		if (FREEROOM <= 3) {
+			len = prevlen;
+			len += sprintf(buf+len, "# truncated\n");
+			break;
+		}
+		prevlen = len;
+	}
+
+	free_page((unsigned long) buffer);
+	return len;
+#undef MANGLE
+#undef FREEROOM
+}
+
+/*
+ * 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);
+
+	if (list_empty(&mnt->mnt_list))
+		return;
+
+	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) {
+		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 && recurse)
+			umount_tree(mnt);
+		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_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;
+
+	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
+		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(&current->fs->lock);
+	user_nd.mnt = mntget(current->fs->rootmnt);
+	user_nd.dentry = dget(current->fs->root);
+	read_unlock(&current->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(&current->fs->lock);
+	old_rootmnt = mntget(current->fs->rootmnt);
+	read_unlock(&current->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(&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
FUNET's LINUX-ADM group, linux-adm@nic.funet.fi
TCL-scripts by Sam Shen (who was at: slshen@lbl.gov)