Cache root in nameidata

New field: nd->root.  When pathname resolution wants to know the root,
check if nd->root.mnt is non-NULL; use nd->root if it is, otherwise
copy current->fs->root there.  After path_walk() is finished, we check
if we'd got a cached value in nd->root and drop it.  Before calling
path_walk() we should either set nd->root.mnt to NULL *or* copy (and
pin down) some path to nd->root.  In the latter case we won't be
looking at current->fs->root at all.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/namei.c b/fs/namei.c
index 895733e..88baaf2 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -552,6 +552,17 @@ static __always_inline int link_path_walk(const char *name, struct nameidata *nd
        return result;
 }
 
+static __always_inline void set_root(struct nameidata *nd)
+{
+       if (!nd->root.mnt) {
+               struct fs_struct *fs = current->fs;
+               read_lock(&fs->lock);
+               nd->root = fs->root;
+               path_get(&nd->root);
+               read_unlock(&fs->lock);
+       }
+}
+
 static __always_inline int __vfs_follow_link(struct nameidata *nd, const char *link)
 {
        int res = 0;
@@ -560,14 +571,10 @@ static __always_inline int __vfs_follow_link(struct nameidata *nd, const char *l
                goto fail;
 
        if (*link == '/') {
-               struct fs_struct *fs = current->fs;
-
+               set_root(nd);
                path_put(&nd->path);
-
-               read_lock(&fs->lock);
-               nd->path = fs->root;
-               path_get(&fs->root);
-               read_unlock(&fs->lock);
+               nd->path = nd->root;
+               path_get(&nd->root);
        }
 
        res = link_path_walk(link, nd);
@@ -741,19 +748,16 @@ int follow_down(struct vfsmount **mnt, struct dentry **dentry)
 
 static __always_inline void follow_dotdot(struct nameidata *nd)
 {
-       struct fs_struct *fs = current->fs;
+       set_root(nd);
 
        while(1) {
                struct vfsmount *parent;
                struct dentry *old = nd->path.dentry;
 
-                read_lock(&fs->lock);
-               if (nd->path.dentry == fs->root.dentry &&
-                   nd->path.mnt == fs->root.mnt) {
-                        read_unlock(&fs->lock);
+               if (nd->path.dentry == nd->root.dentry &&
+                   nd->path.mnt == nd->root.mnt) {
                        break;
                }
-                read_unlock(&fs->lock);
                spin_lock(&dcache_lock);
                if (nd->path.dentry != nd->path.mnt->mnt_root) {
                        nd->path.dentry = dget(nd->path.dentry->d_parent);
@@ -1022,18 +1026,18 @@ static int path_init(int dfd, const char *name, unsigned int flags, struct namei
        int retval = 0;
        int fput_needed;
        struct file *file;
-       struct fs_struct *fs = current->fs;
 
        nd->last_type = LAST_ROOT; /* if there are only slashes... */
        nd->flags = flags;
        nd->depth = 0;
+       nd->root.mnt = NULL;
 
        if (*name=='/') {
-               read_lock(&fs->lock);
-               nd->path = fs->root;
-               path_get(&fs->root);
-               read_unlock(&fs->lock);
+               set_root(nd);
+               nd->path = nd->root;
+               path_get(&nd->root);
        } else if (dfd == AT_FDCWD) {
+               struct fs_struct *fs = current->fs;
                read_lock(&fs->lock);
                nd->path = fs->pwd;
                path_get(&fs->pwd);
@@ -1079,6 +1083,10 @@ static int do_path_lookup(int dfd, const char *name,
        if (unlikely(!retval && !audit_dummy_context() && nd->path.dentry &&
                                nd->path.dentry->d_inode))
                audit_inode(name, nd->path.dentry);
+       if (nd->root.mnt) {
+               path_put(&nd->root);
+               nd->root.mnt = NULL;
+       }
        return retval;
 }
 
@@ -1115,6 +1123,7 @@ int vfs_path_lookup(struct dentry *dentry, struct vfsmount *mnt,
        nd->last_type = LAST_ROOT;
        nd->flags = flags;
        nd->depth = 0;
+       nd->root.mnt = NULL;
 
        nd->path.dentry = dentry;
        nd->path.mnt = mnt;
@@ -1125,8 +1134,12 @@ int vfs_path_lookup(struct dentry *dentry, struct vfsmount *mnt,
                                nd->path.dentry->d_inode))
                audit_inode(name, nd->path.dentry);
 
-       return retval;
+       if (nd->root.mnt) {
+               path_put(&nd->root);
+               nd->root.mnt = NULL;
+       }
 
+       return retval;
 }
 
 /**
@@ -1817,6 +1830,8 @@ exit:
        if (!IS_ERR(nd.intent.open.file))
                release_open_intent(&nd);
 exit_parent:
+       if (nd.root.mnt)
+               path_put(&nd.root);
        path_put(&nd.path);
        return ERR_PTR(error);
 

diff --git a/include/linux/namei.h b/include/linux/namei.h
index 518098f..325dd3a 100644 (file)
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -18,6 +18,7 @@ enum { MAX_NESTED_LINKS = 8 };
 struct nameidata {
        struct path     path;
        struct qstr     last;
+       struct path     root;
        unsigned int    flags;
        int             last_type;
        unsigned        depth;