fs: introduce vfs_path_lookup (16f18200) · Commits · 戴 / test

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 <jsipek@cs.sunysb.edu> Cc: Al Viro <viro@zeniv.linux.org.uk> Acked-by:

Christoph Hellwig <hch@lst.de> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Cc: Neil Brown <neilb@suse.de> Cc: Michael Halcrow <mhalcrow@us.ibm.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

fs/namei.c

+32 −0

Original line number	Diff line number	Diff line
		@@ -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);

include/linux/namei.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -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 *);

Admin message