From 16f1820028d660d9da9c03b2ae7e98253c11795b Mon Sep 17 00:00:00 2001 From: Josef 'Jeff' Sipek Date: Thu, 19 Jul 2007 01:48:18 -0700 Subject: [PATCH] fs: introduce vfs_path_lookup Stackable file systems, among others, frequently need to lookup paths or path components starting from an arbitrary point in the namespace (identified by a dentry and a vfsmount). Currently, such file systems use lookup_one_len, which is frowned upon [1] as it does not pass the lookup intent along; not passing a lookup intent, for example, can trigger BUG_ON's when stacking on top of NFSv4. The first patch introduces a new lookup function to allow lookup starting from an arbitrary point in the namespace. This approach has been suggested by Christoph Hellwig [2]. The second patch changes sunrpc to use vfs_path_lookup. The third patch changes nfsctl.c to use vfs_path_lookup. The fourth patch marks link_path_walk static. The fifth, and last patch, unexports path_walk because it is no longer unnecessary to call it directly, and using the new vfs_path_lookup is cleaner. For example, the following snippet of code, looks up "some/path/component" in a directory pointed to by parent_{dentry,vfsmnt}: err = vfs_path_lookup(parent_dentry, parent_vfsmnt, "some/path/component", 0, &nd); if (!err) { /* exits */ ... /* once done, release the references */ path_release(&nd); } else if (err == -ENOENT) { /* doesn't exist */ } else { /* other error */ } VFS functions such as lookup_create can be used on the nameidata structure to pass the create intent to the file system. Signed-off-by: Josef 'Jeff' Sipek Cc: Al Viro Acked-by: Christoph Hellwig Cc: Trond Myklebust Cc: Neil Brown Cc: Michael Halcrow Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/namei.c | 32 ++++++++++++++++++++++++++++++++ include/linux/namei.h | 2 ++ 2 files changed, 34 insertions(+) diff --git a/fs/namei.c b/fs/namei.c index defaa47c11d4..3bdb29615a9d 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -1172,6 +1172,37 @@ int fastcall path_lookup(const char *name, unsigned int flags, return do_path_lookup(AT_FDCWD, name, flags, nd); } +/** + * vfs_path_lookup - lookup a file path relative to a dentry-vfsmount pair + * @dentry: pointer to dentry of the base directory + * @mnt: pointer to vfs mount of the base directory + * @name: pointer to file name + * @flags: lookup flags + * @nd: pointer to nameidata + */ +int vfs_path_lookup(struct dentry *dentry, struct vfsmount *mnt, + const char *name, unsigned int flags, + struct nameidata *nd) +{ + int retval; + + /* same as do_path_lookup */ + nd->last_type = LAST_ROOT; + nd->flags = flags; + nd->depth = 0; + + nd->mnt = mntget(mnt); + nd->dentry = dget(dentry); + + retval = path_walk(name, nd); + if (unlikely(!retval && !audit_dummy_context() && nd->dentry && + nd->dentry->d_inode)) + audit_inode(name, nd->dentry->d_inode); + + return retval; + +} + static int __path_lookup_intent_open(int dfd, const char *name, unsigned int lookup_flags, struct nameidata *nd, int open_flags, int create_mode) @@ -2774,6 +2805,7 @@ EXPORT_SYMBOL(__page_symlink); EXPORT_SYMBOL(page_symlink); EXPORT_SYMBOL(page_symlink_inode_operations); EXPORT_SYMBOL(path_lookup); +EXPORT_SYMBOL(vfs_path_lookup); EXPORT_SYMBOL(path_release); EXPORT_SYMBOL(path_walk); EXPORT_SYMBOL(permission); diff --git a/include/linux/namei.h b/include/linux/namei.h index b7dd24917f0d..2e21af0989d9 100644 --- a/include/linux/namei.h +++ b/include/linux/namei.h @@ -69,6 +69,8 @@ extern int FASTCALL(__user_walk_fd(int dfd, const char __user *, unsigned, struc #define user_path_walk_link(name,nd) \ __user_walk_fd(AT_FDCWD, name, 0, nd) extern int FASTCALL(path_lookup(const char *, unsigned, struct nameidata *)); +extern int vfs_path_lookup(struct dentry *, struct vfsmount *, + const char *, unsigned int, struct nameidata *); extern int FASTCALL(path_walk(const char *, struct nameidata *)); extern int FASTCALL(link_path_walk(const char *, struct nameidata *)); extern void path_release(struct nameidata *); -- 2.20.1