Commit 756daf26 authored by NeilBrown's avatar NeilBrown Committed by Al Viro
Browse files

VFS: replace {, total_}link_count in task_struct with pointer to nameidata 



task_struct currently contains two ad-hoc members for use by the VFS:
link_count and total_link_count.  These are only interesting to fs/namei.c,
so exposing them explicitly is poor layering.  Incidentally, link_count
isn't used anymore, so it can just die.

This patches replaces those with a single pointer to 'struct nameidata'.
This structure represents the current filename lookup of which
there can only be one per process, and is a natural place to
store total_link_count.

This will allow the current "nameidata" argument to all
follow_link operations to be removed as current->nameidata
can be used instead in the _very_ few instances that care about
it at all.

As there are occasional circumstances where pathname lookup can
recurse, such as through kern_path_locked, we always save and old
current->nameidata (if there is one) when setting a new value, and
make sure any active link_counts are preserved.

follow_mount and follow_automount now get a 'struct nameidata *'
rather than 'int flags' so that they can directly access
total_link_count, rather than going through 'current'.

Suggested-by: default avatarAl Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: default avatarNeilBrown <neilb@suse.de>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 44163f30

fs/namei.c

+39 −31
Original line number Diff line number Diff line
@@ -505,6 +505,7 @@ struct nameidata { 
	unsigned	seq, m_seq;

	int		last_type;

	unsigned	depth;

	int		total_link_count;

	struct file	*base;

	struct saved {

		struct path link;
@@ -513,16 +514,25 @@ struct nameidata { 
	} *stack, internal[EMBEDDED_LEVELS];

};



static void set_nameidata(struct nameidata *nd)

static struct nameidata *set_nameidata(struct nameidata *p)

{

	nd->stack = nd->internal;

	struct nameidata *old = current->nameidata;

	p->stack = p->internal;

	p->total_link_count = old ? old->total_link_count : 0;

	current->nameidata = p;

	return old;

}



static void restore_nameidata(struct nameidata *nd)

static void restore_nameidata(struct nameidata *old)

{

	if (nd->stack != nd->internal) {

		kfree(nd->stack);

		nd->stack = nd->internal;

	struct nameidata *now = current->nameidata;



	current->nameidata = old;

	if (old)

		old->total_link_count = now->total_link_count;

	if (now->stack != now->internal) {

		kfree(now->stack);

		now->stack = now->internal;

	}

}
@@ -970,7 +980,7 @@ EXPORT_SYMBOL(follow_up); 
 * - return -EISDIR to tell follow_managed() to stop and return the path we

 *   were called with.

 */

static int follow_automount(struct path *path, unsigned flags,

static int follow_automount(struct path *path, struct nameidata *nd,

			    bool *need_mntput)

{

	struct vfsmount *mnt;
@@ -990,13 +1000,13 @@ static int follow_automount(struct path *path, unsigned flags, 
	 * as being automount points.  These will need the attentions

	 * of the daemon to instantiate them before they can be used.

	 */

	if (!(flags & (LOOKUP_PARENT | LOOKUP_DIRECTORY |

	if (!(nd->flags & (LOOKUP_PARENT | LOOKUP_DIRECTORY |

			   LOOKUP_OPEN | LOOKUP_CREATE | LOOKUP_AUTOMOUNT)) &&

	    path->dentry->d_inode)

		return -EISDIR;



	current->total_link_count++;

	if (current->total_link_count >= 40)

	nd->total_link_count++;

	if (nd->total_link_count >= 40)

		return -ELOOP;



	mnt = path->dentry->d_op->d_automount(path);
@@ -1010,7 +1020,7 @@ static int follow_automount(struct path *path, unsigned flags, 
		 * the path being looked up; if it wasn't then the remainder of

		 * the path is inaccessible and we should say so.

		 */

		if (PTR_ERR(mnt) == -EISDIR && (flags & LOOKUP_PARENT))

		if (PTR_ERR(mnt) == -EISDIR && (nd->flags & LOOKUP_PARENT))

			return -EREMOTE;

		return PTR_ERR(mnt);

	}
@@ -1050,7 +1060,7 @@ static int follow_automount(struct path *path, unsigned flags, 
 *

 * Serialization is taken care of in namespace.c

 */

static int follow_managed(struct path *path, unsigned flags)

static int follow_managed(struct path *path, struct nameidata *nd)

{

	struct vfsmount *mnt = path->mnt; /* held by caller, must be left alone */

	unsigned managed;
@@ -1094,7 +1104,7 @@ static int follow_managed(struct path *path, unsigned flags) 


		/* Handle an automount point */

		if (managed & DCACHE_NEED_AUTOMOUNT) {

			ret = follow_automount(path, flags, &need_mntput);

			ret = follow_automount(path, nd, &need_mntput);

			if (ret < 0)

				break;

			continue;
@@ -1483,7 +1493,7 @@ unlazy: 
	}

	path->mnt = mnt;

	path->dentry = dentry;

	err = follow_managed(path, nd->flags);

	err = follow_managed(path, nd);

	if (unlikely(err < 0)) {

		path_put_conditional(path, nd);

		return err;
@@ -1513,7 +1523,7 @@ static int lookup_slow(struct nameidata *nd, struct path *path) 
		return PTR_ERR(dentry);

	path->mnt = nd->path.mnt;

	path->dentry = dentry;

	err = follow_managed(path, nd->flags);

	err = follow_managed(path, nd);

	if (unlikely(err < 0)) {

		path_put_conditional(path, nd);

		return err;
@@ -1563,7 +1573,7 @@ static void terminate_walk(struct nameidata *nd) 
static int pick_link(struct nameidata *nd, struct path *link)

{

	int error;

	if (unlikely(current->total_link_count++ >= MAXSYMLINKS)) {

	if (unlikely(nd->total_link_count++ >= MAXSYMLINKS)) {

		path_to_nameidata(link, nd);

		return -ELOOP;

	}
@@ -1981,7 +1991,7 @@ static int path_init(int dfd, const struct filename *name, unsigned int flags, 
	rcu_read_unlock();

	return -ECHILD;

done:

	current->total_link_count = 0;

	nd->total_link_count = 0;

	return link_path_walk(s, nd);

}
@@ -2087,10 +2097,9 @@ static int filename_lookup(int dfd, struct filename *name, 
				unsigned int flags, struct nameidata *nd)

{

	int retval;

	struct nameidata *saved_nd = set_nameidata(nd);



	set_nameidata(nd);

	retval = path_lookupat(dfd, name, flags | LOOKUP_RCU, nd);



	if (unlikely(retval == -ECHILD))

		retval = path_lookupat(dfd, name, flags, nd);

	if (unlikely(retval == -ESTALE))
@@ -2098,7 +2107,7 @@ static int filename_lookup(int dfd, struct filename *name, 


	if (likely(!retval))

		audit_inode(name, nd->path.dentry, flags & LOOKUP_PARENT);

	restore_nameidata(nd);

	restore_nameidata(saved_nd);

	return retval;

}
@@ -2426,11 +2435,11 @@ static int 
filename_mountpoint(int dfd, struct filename *name, struct path *path,

			unsigned int flags)

{

	struct nameidata nd;

	struct nameidata nd, *saved;

	int error;

	if (IS_ERR(name))

		return PTR_ERR(name);

	set_nameidata(&nd);

	saved = set_nameidata(&nd);

	error = path_mountpoint(dfd, name, path, &nd, flags | LOOKUP_RCU);

	if (unlikely(error == -ECHILD))

		error = path_mountpoint(dfd, name, path, &nd, flags);
@@ -2438,7 +2447,7 @@ filename_mountpoint(int dfd, struct filename *name, struct path *path, 
		error = path_mountpoint(dfd, name, path, &nd, flags | LOOKUP_REVAL);

	if (likely(!error))

		audit_inode(name, path->dentry, 0);

	restore_nameidata(&nd);

	restore_nameidata(saved);

	putname(name);

	return error;

}
@@ -3087,7 +3096,7 @@ retry_lookup: 
	if ((open_flag & (O_EXCL | O_CREAT)) == (O_EXCL | O_CREAT))

		goto exit_dput;



	error = follow_managed(&path, nd->flags);

	error = follow_managed(&path, nd);

	if (error < 0)

		goto exit_dput;
@@ -3323,31 +3332,29 @@ out2: 
struct file *do_filp_open(int dfd, struct filename *pathname,

		const struct open_flags *op)

{

	struct nameidata nd;

	struct nameidata nd, *saved_nd = set_nameidata(&nd);

	int flags = op->lookup_flags;

	struct file *filp;



	set_nameidata(&nd);

	filp = path_openat(dfd, pathname, &nd, op, flags | LOOKUP_RCU);

	if (unlikely(filp == ERR_PTR(-ECHILD)))

		filp = path_openat(dfd, pathname, &nd, op, flags);

	if (unlikely(filp == ERR_PTR(-ESTALE)))

		filp = path_openat(dfd, pathname, &nd, op, flags | LOOKUP_REVAL);

	restore_nameidata(&nd);

	restore_nameidata(saved_nd);

	return filp;

}



struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt,

		const char *name, const struct open_flags *op)

{

	struct nameidata nd;

	struct nameidata nd, *saved_nd;

	struct file *file;

	struct filename *filename;

	int flags = op->lookup_flags | LOOKUP_ROOT;



	nd.root.mnt = mnt;

	nd.root.dentry = dentry;

	set_nameidata(&nd);



	if (d_is_symlink(dentry) && op->intent & LOOKUP_OPEN)

		return ERR_PTR(-ELOOP);
@@ -3356,12 +3363,13 @@ struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt, 
	if (unlikely(IS_ERR(filename)))

		return ERR_CAST(filename);



	saved_nd = set_nameidata(&nd);

	file = path_openat(-1, filename, &nd, op, flags | LOOKUP_RCU);

	if (unlikely(file == ERR_PTR(-ECHILD)))

		file = path_openat(-1, filename, &nd, op, flags);

	if (unlikely(file == ERR_PTR(-ESTALE)))

		file = path_openat(-1, filename, &nd, op, flags | LOOKUP_REVAL);

	restore_nameidata(&nd);

	restore_nameidata(saved_nd);

	putname(filename);

	return file;

}

include/linux/sched.h

+1 −1
Original line number Diff line number Diff line
@@ -1461,7 +1461,7 @@ struct task_struct { 
				       it with task_lock())

				     - initialized normally by setup_new_exec */

/* file system info */

	int link_count, total_link_count;

	struct nameidata *nameidata;

#ifdef CONFIG_SYSVIPC

/* ipc stuff */

	struct sysv_sem sysvsem;

CRA Git | Maintained and supported by SUSTech CRA and CCSE