Commit 5b6ca027 authored by Al Viro's avatar Al Viro
Browse files

reduce vfs_path_lookup() to do_path_lookup() 



New lookup flag: LOOKUP_ROOT.  nd->root is set (and held) by caller,
path_init() starts walking from that place and all pathname resolution
machinery never drops nd->root if that flag is set.  That turns
vfs_path_lookup() into a special case of do_path_lookup() *and*
gets us down to 3 callers of link_path_walk(), making it finally
feasible to rip the handling of trailing symlink out of link_path_walk().
That will not only simply the living hell out of it, but make life
much simpler for unionfs merge.  Trailing symlink handling will
become iterative, which is a good thing for stack footprint in
a lot of situations as well.

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 5a18fff2

fs/namei.c

+43 −52
Original line number Diff line number Diff line
@@ -401,9 +401,11 @@ static int nameidata_drop_rcu(struct nameidata *nd) 
{

	struct fs_struct *fs = current->fs;

	struct dentry *dentry = nd->path.dentry;

	int want_root = 0;



	BUG_ON(!(nd->flags & LOOKUP_RCU));

	if (nd->root.mnt) {

	if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {

		want_root = 1;

		spin_lock(&fs->lock);

		if (nd->root.mnt != fs->root.mnt ||

				nd->root.dentry != fs->root.dentry)
@@ -414,7 +416,7 @@ static int nameidata_drop_rcu(struct nameidata *nd) 
		goto err;

	BUG_ON(nd->inode != dentry->d_inode);

	spin_unlock(&dentry->d_lock);

	if (nd->root.mnt) {

	if (want_root) {

		path_get(&nd->root);

		spin_unlock(&fs->lock);

	}
@@ -427,7 +429,7 @@ static int nameidata_drop_rcu(struct nameidata *nd) 
err:

	spin_unlock(&dentry->d_lock);

err_root:

	if (nd->root.mnt)

	if (want_root)

		spin_unlock(&fs->lock);

	return -ECHILD;

}
@@ -454,9 +456,11 @@ static int nameidata_dentry_drop_rcu(struct nameidata *nd, struct dentry *dentry 
{

	struct fs_struct *fs = current->fs;

	struct dentry *parent = nd->path.dentry;

	int want_root = 0;



	BUG_ON(!(nd->flags & LOOKUP_RCU));

	if (nd->root.mnt) {

	if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {

		want_root = 1;

		spin_lock(&fs->lock);

		if (nd->root.mnt != fs->root.mnt ||

				nd->root.dentry != fs->root.dentry)
@@ -476,7 +480,7 @@ static int nameidata_dentry_drop_rcu(struct nameidata *nd, struct dentry *dentry 
	parent->d_count++;

	spin_unlock(&dentry->d_lock);

	spin_unlock(&parent->d_lock);

	if (nd->root.mnt) {

	if (want_root) {

		path_get(&nd->root);

		spin_unlock(&fs->lock);

	}
@@ -490,7 +494,7 @@ err: 
	spin_unlock(&dentry->d_lock);

	spin_unlock(&parent->d_lock);

err_root:

	if (nd->root.mnt)

	if (want_root)

		spin_unlock(&fs->lock);

	return -ECHILD;

}
@@ -501,6 +505,7 @@ static inline int nameidata_dentry_drop_rcu_maybe(struct nameidata *nd, struct d 
	if (nd->flags & LOOKUP_RCU) {

		if (unlikely(nameidata_dentry_drop_rcu(nd, dentry))) {

			nd->flags &= ~LOOKUP_RCU;

			if (!(nd->flags & LOOKUP_ROOT))

				nd->root.mnt = NULL;

			rcu_read_unlock();

			br_read_unlock(vfsmount_lock);
@@ -525,6 +530,7 @@ static int nameidata_drop_rcu_last(struct nameidata *nd) 


	BUG_ON(!(nd->flags & LOOKUP_RCU));

	nd->flags &= ~LOOKUP_RCU;

	if (!(nd->flags & LOOKUP_ROOT))

		nd->root.mnt = NULL;

	spin_lock(&dentry->d_lock);

	if (!__d_rcu_to_refcount(dentry, nd->seq))
@@ -1053,6 +1059,7 @@ static int follow_dotdot_rcu(struct nameidata *nd) 


failed:

	nd->flags &= ~LOOKUP_RCU;

	if (!(nd->flags & LOOKUP_ROOT))

		nd->root.mnt = NULL;

	rcu_read_unlock();

	br_read_unlock(vfsmount_lock);
@@ -1310,6 +1317,7 @@ static void terminate_walk(struct nameidata *nd) 
		path_put(&nd->path);

	} else {

		nd->flags &= ~LOOKUP_RCU;

		if (!(nd->flags & LOOKUP_ROOT))

			nd->root.mnt = NULL;

		rcu_read_unlock();

		br_read_unlock(vfsmount_lock);
@@ -1477,6 +1485,25 @@ static int path_init(int dfd, const char *name, unsigned int flags, 
	nd->last_type = LAST_ROOT; /* if there are only slashes... */

	nd->flags = flags | LOOKUP_JUMPED;

	nd->depth = 0;

	if (flags & LOOKUP_ROOT) {

		struct inode *inode = nd->root.dentry->d_inode;

		if (!inode->i_op->lookup)

			return -ENOTDIR;

		retval = inode_permission(inode, MAY_EXEC);

		if (retval)

			return retval;

		nd->path = nd->root;

		nd->inode = inode;

		if (flags & LOOKUP_RCU) {

			br_read_lock(vfsmount_lock);

			rcu_read_lock();

			nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);

		} else {

			path_get(&nd->path);

		}

		return 0;

	}



	nd->root.mnt = NULL;



	if (*name=='/') {
@@ -1587,7 +1614,7 @@ static int path_lookupat(int dfd, const char *name, 
	if (base)

		fput(base);



	if (nd->root.mnt) {

	if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {

		path_put(&nd->root);

		nd->root.mnt = NULL;

	}
@@ -1638,46 +1665,10 @@ int vfs_path_lookup(struct dentry *dentry, struct vfsmount *mnt, 
		    const char *name, unsigned int flags,

		    struct nameidata *nd)

{

	int result;



	/* same as do_path_lookup */

	nd->last_type = LAST_ROOT;

	nd->flags = flags | LOOKUP_JUMPED;

	nd->depth = 0;



	nd->path.dentry = dentry;

	nd->path.mnt = mnt;

	path_get(&nd->path);

	nd->root = nd->path;

	path_get(&nd->root);

	nd->inode = nd->path.dentry->d_inode;



	current->total_link_count = 0;



	result = link_path_walk(name, nd);

	if (!result)

		result = handle_reval_path(nd);

	if (result == -ESTALE) {

		/* nd->path had been dropped */

		current->total_link_count = 0;

		nd->path.dentry = dentry;

		nd->path.mnt = mnt;

		nd->inode = dentry->d_inode;

		path_get(&nd->path);

		nd->flags = flags | LOOKUP_JUMPED | LOOKUP_REVAL;



		result = link_path_walk(name, nd);

		if (!result)

			result = handle_reval_path(nd);

	}

	if (unlikely(!result && !audit_dummy_context() && nd->path.dentry &&

				nd->inode))

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



	path_put(&nd->root);

	nd->root.mnt = NULL;



	return result;

	nd->root.dentry = dentry;

	nd->root.mnt = mnt;

	/* the first argument of do_path_lookup() is ignored with LOOKUP_ROOT */

	return do_path_lookup(AT_FDCWD, name, flags | LOOKUP_ROOT, nd);

}



static struct dentry *__lookup_hash(struct qstr *name,
@@ -2320,7 +2311,7 @@ static struct file *path_openat(int dfd, const char *pathname, 
		path_put(&link);

	}

out:

	if (nd.root.mnt)

	if (nd.root.mnt && !(nd.flags & LOOKUP_ROOT))

		path_put(&nd.root);

	if (base)

		fput(base);

include/linux/namei.h

+1 −0
Original line number Diff line number Diff line
@@ -63,6 +63,7 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND}; 
#define LOOKUP_RENAME_TARGET	0x0800



#define LOOKUP_JUMPED		0x1000

#define LOOKUP_ROOT		0x2000



extern int user_path_at(int, const char __user *, unsigned, struct path *);

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