open-style analog of vfs_path_lookup()

new function: file_open_root(dentry, mnt, name, flags) opens the file
vfs_path_lookup would arrive to.

Note that name can be empty; in that case the usual requirement that
dentry should be a directory is lifted.

open-coded equivalents switched to it, may_open() got down exactly
one caller and became static.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/um/drivers/mconsole_kern.c

@@ -124,35 +124,18 @@ void mconsole_log(struct mc_request *req)
 #if 0
 void mconsole_proc(struct mc_request *req)
 {
-	struct nameidata nd;
 	struct vfsmount *mnt = current->nsproxy->pid_ns->proc_mnt;
 	struct file *file;
-	int n, err;
+	int n;
 	char *ptr = req->request.data, *buf;
 	mm_segment_t old_fs = get_fs();
 
 	ptr += strlen("proc");
 	ptr = skip_spaces(ptr);
 
-	err = vfs_path_lookup(mnt->mnt_root, mnt, ptr, LOOKUP_FOLLOW, &nd);
-	if (err) {
-		mconsole_reply(req, "Failed to look up file", 1, 0);
-		goto out;
-	}
-
-	err = may_open(&nd.path, MAY_READ, O_RDONLY);
-	if (result) {
-		mconsole_reply(req, "Failed to open file", 1, 0);
-		path_put(&nd.path);
-		goto out;
-	}
-
-	file = dentry_open(nd.path.dentry, nd.path.mnt, O_RDONLY,
-			   current_cred());
-	err = PTR_ERR(file);
+	file = file_open_root(mnt->mnt_root, mnt, ptr, O_RDONLY);
 	if (IS_ERR(file)) {
 		mconsole_reply(req, "Failed to open file", 1, 0);
-		path_put(&nd.path);
 		goto out;
 	}
 

fs/internal.h

@@ -114,6 +114,8 @@ struct open_flags {
 };
 extern struct file *do_filp_open(int dfd, const char *pathname,
 		const struct open_flags *op, int lookup_flags);
+extern struct file *do_file_open_root(struct dentry *, struct vfsmount *,
+		const char *, const struct open_flags *, int lookup_flags);
 
 /*
  * inode.c

fs/namei.c

@@ -1487,11 +1487,13 @@ static int path_init(int dfd, const char *name, unsigned int flags,
 	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;
+		if (*name) {
+			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) {
@@ -1937,7 +1939,7 @@ int vfs_create(struct inode *dir, struct dentry *dentry, int mode,
 	return error;
 }
 
-int may_open(struct path *path, int acc_mode, int flag)
+static int may_open(struct path *path, int acc_mode, int flag)
 {
 	struct dentry *dentry = path->dentry;
 	struct inode *inode = dentry->d_inode;
@@ -2250,11 +2252,10 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
 }
 
 static struct file *path_openat(int dfd, const char *pathname,
-		const struct open_flags *op, int flags)
+		struct nameidata *nd, const struct open_flags *op, int flags)
 {
 	struct file *base = NULL;
 	struct file *filp;
-	struct nameidata nd;
 	struct path path;
 	int count = 0;
 	int error;
@@ -2264,27 +2265,27 @@ static struct file *path_openat(int dfd, const char *pathname,
 		return ERR_PTR(-ENFILE);
 
 	filp->f_flags = op->open_flag;
-	nd.intent.open.file = filp;
-	nd.intent.open.flags = open_to_namei_flags(op->open_flag);
-	nd.intent.open.create_mode = op->mode;
+	nd->intent.open.file = filp;
+	nd->intent.open.flags = open_to_namei_flags(op->open_flag);
+	nd->intent.open.create_mode = op->mode;
 
-	error = path_init(dfd, pathname, flags | LOOKUP_PARENT, &nd, &base);
+	error = path_init(dfd, pathname, flags | LOOKUP_PARENT, nd, &base);
 	if (unlikely(error))
 		goto out_filp;
 
 	current->total_link_count = 0;
-	error = link_path_walk(pathname, &nd);
+	error = link_path_walk(pathname, nd);
 	if (unlikely(error))
 		goto out_filp;
 
-	filp = do_last(&nd, &path, op, pathname);
+	filp = do_last(nd, &path, op, pathname);
 	while (unlikely(!filp)) { /* trailing symlink */
 		struct path link = path;
 		struct inode *linki = link.dentry->d_inode;
 		void *cookie;
-		if (!(nd.flags & LOOKUP_FOLLOW) || count++ == 32) {
-			path_put_conditional(&path, &nd);
-			path_put(&nd.path);
+		if (!(nd->flags & LOOKUP_FOLLOW) || count++ == 32) {
+			path_put_conditional(&path, nd);
+			path_put(&nd->path);
 			filp = ERR_PTR(-ELOOP);
 			break;
 		}
@@ -2299,23 +2300,23 @@ static struct file *path_openat(int dfd, const char *pathname,
 		 * have to putname() it when we are done. Procfs-like symlinks
 		 * just set LAST_BIND.
 		 */
-		nd.flags |= LOOKUP_PARENT;
-		nd.flags &= ~(LOOKUP_OPEN|LOOKUP_CREATE|LOOKUP_EXCL);
-		error = __do_follow_link(&link, &nd, &cookie);
+		nd->flags |= LOOKUP_PARENT;
+		nd->flags &= ~(LOOKUP_OPEN|LOOKUP_CREATE|LOOKUP_EXCL);
+		error = __do_follow_link(&link, nd, &cookie);
 		if (unlikely(error))
 			filp = ERR_PTR(error);
 		else
-			filp = do_last(&nd, &path, op, pathname);
+			filp = do_last(nd, &path, op, pathname);
 		if (!IS_ERR(cookie) && linki->i_op->put_link)
-			linki->i_op->put_link(link.dentry, &nd, cookie);
+			linki->i_op->put_link(link.dentry, nd, cookie);
 		path_put(&link);
 	}
 out:
-	if (nd.root.mnt && !(nd.flags & LOOKUP_ROOT))
-		path_put(&nd.root);
+	if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT))
+		path_put(&nd->root);
 	if (base)
 		fput(base);
-	release_open_intent(&nd);
+	release_open_intent(nd);
 	return filp;
 
 out_filp:
@@ -2326,16 +2327,39 @@ static struct file *path_openat(int dfd, const char *pathname,
 struct file *do_filp_open(int dfd, const char *pathname,
 		const struct open_flags *op, int flags)
 {
+	struct nameidata nd;
 	struct file *filp;
 
-	filp = path_openat(dfd, pathname, op, flags | LOOKUP_RCU);
+	filp = path_openat(dfd, pathname, &nd, op, flags | LOOKUP_RCU);
 	if (unlikely(filp == ERR_PTR(-ECHILD)))
-		filp = path_openat(dfd, pathname, op, flags);
+		filp = path_openat(dfd, pathname, &nd, op, flags);
 	if (unlikely(filp == ERR_PTR(-ESTALE)))
-		filp = path_openat(dfd, pathname, op, flags | LOOKUP_REVAL);
+		filp = path_openat(dfd, pathname, &nd, op, flags | LOOKUP_REVAL);
 	return filp;
 }
 
+struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt,
+		const char *name, const struct open_flags *op, int flags)
+{
+	struct nameidata nd;
+	struct file *file;
+
+	nd.root.mnt = mnt;
+	nd.root.dentry = dentry;
+
+	flags |= LOOKUP_ROOT;
+
+	if (dentry->d_inode->i_op->follow_link)
+		return ERR_PTR(-ELOOP);
+
+	file = path_openat(-1, name, &nd, op, flags | LOOKUP_RCU);
+	if (unlikely(file == ERR_PTR(-ECHILD)))
+		file = path_openat(-1, name, &nd, op, flags);
+	if (unlikely(file == ERR_PTR(-ESTALE)))
+		file = path_openat(-1, name, &nd, op, flags | LOOKUP_REVAL);
+	return file;
+}
+
 /**
  * lookup_create - lookup a dentry, creating it if it doesn't exist
  * @nd: nameidata info

fs/nfsctl.c

@@ -22,30 +22,17 @@
 
 static struct file *do_open(char *name, int flags)
 {
-	struct nameidata nd;
 	struct vfsmount *mnt;
-	int error;
+	struct file *file;
 
 	mnt = do_kern_mount("nfsd", 0, "nfsd", NULL);
 	if (IS_ERR(mnt))
 		return (struct file *)mnt;
 
-	error = vfs_path_lookup(mnt->mnt_root, mnt, name, 0, &nd);
-	mntput(mnt);	/* drop do_kern_mount reference */
-	if (error)
-		return ERR_PTR(error);
-
-	if (flags == O_RDWR)
-		error = may_open(&nd.path, MAY_READ|MAY_WRITE, flags);
-	else
-		error = may_open(&nd.path, MAY_WRITE, flags);
+	file = file_open_root(mnt->mnt_root, mnt, name, flags);
 
-	if (!error)
-		return dentry_open(nd.path.dentry, nd.path.mnt, flags,
-				   current_cred());
-
-	path_put(&nd.path);
-	return ERR_PTR(error);
+	mntput(mnt);	/* drop do_kern_mount reference */
+	return file;
 }
 
 static struct {

fs/open.c

@@ -959,6 +959,20 @@ struct file *filp_open(const char *filename, int flags, int mode)
 }
 EXPORT_SYMBOL(filp_open);
 
+struct file *file_open_root(struct dentry *dentry, struct vfsmount *mnt,
+			    const char *filename, int flags)
+{
+	struct open_flags op;
+	int lookup = build_open_flags(flags, 0, &op);
+	if (flags & O_CREAT)
+		return ERR_PTR(-EINVAL);
+	if (!filename && (flags & O_DIRECTORY))
+		if (!dentry->d_inode->i_op->lookup)
+			return ERR_PTR(-ENOTDIR);
+	return do_file_open_root(dentry, mnt, filename, &op, lookup);
+}
+EXPORT_SYMBOL(file_open_root);
+
 long do_sys_open(int dfd, const char __user *filename, int flags, int mode)
 {
 	struct open_flags op;

include/linux/fs.h

@@ -1990,6 +1990,8 @@ extern int do_fallocate(struct file *file, int mode, loff_t offset,
 extern long do_sys_open(int dfd, const char __user *filename, int flags,
 			int mode);
 extern struct file *filp_open(const char *, int, int);
+extern struct file *file_open_root(struct dentry *, struct vfsmount *,
+				   const char *, int);
 extern struct file * dentry_open(struct dentry *, struct vfsmount *, int,
 				 const struct cred *);
 extern int filp_close(struct file *, fl_owner_t id);
@@ -2205,8 +2207,6 @@ extern struct file *create_read_pipe(struct file *f, int flags);
 extern struct file *create_write_pipe(int flags);
 extern void free_write_pipe(struct file *);
 
-extern int may_open(struct path *, int, int);
-
 extern int kernel_read(struct file *, loff_t, char *, unsigned long);
 extern struct file * open_exec(const char *);
  

kernel/sysctl_binary.c

@@ -1321,13 +1321,11 @@ static ssize_t binary_sysctl(const int *name, int nlen,
 	void __user *oldval, size_t oldlen, void __user *newval, size_t newlen)
 {
 	const struct bin_table *table = NULL;
-	struct nameidata nd;
 	struct vfsmount *mnt;
 	struct file *file;
 	ssize_t result;
 	char *pathname;
 	int flags;
-	int acc_mode;
 
 	pathname = sysctl_getname(name, nlen, &table);
 	result = PTR_ERR(pathname);
@@ -1337,28 +1335,17 @@ static ssize_t binary_sysctl(const int *name, int nlen,
 	/* How should the sysctl be accessed? */
 	if (oldval && oldlen && newval && newlen) {
 		flags = O_RDWR;
-		acc_mode = MAY_READ | MAY_WRITE;
 	} else if (newval && newlen) {
 		flags = O_WRONLY;
-		acc_mode = MAY_WRITE;
 	} else if (oldval && oldlen) {
 		flags = O_RDONLY;
-		acc_mode = MAY_READ;
 	} else {
 		result = 0;
 		goto out_putname;
 	}
 
 	mnt = current->nsproxy->pid_ns->proc_mnt;
-	result = vfs_path_lookup(mnt->mnt_root, mnt, pathname, 0, &nd);
-	if (result)
-		goto out_putname;
-
-	result = may_open(&nd.path, acc_mode, flags);
-	if (result)
-		goto out_putpath;
-
-	file = dentry_open(nd.path.dentry, nd.path.mnt, flags, current_cred());
+	file = file_open_root(mnt->mnt_root, mnt, pathname, flags);
 	result = PTR_ERR(file);
 	if (IS_ERR(file))
 		goto out_putname;
@@ -1370,10 +1357,6 @@ static ssize_t binary_sysctl(const int *name, int nlen,
 	putname(pathname);
 out:
 	return result;
-
-out_putpath:
-	path_put(&nd.path);
-	goto out_putname;
 }