[PATCH] vfs: *at functions: core

Here is a series of patches which introduce in total 13 new system calls
which take a file descriptor/filename pair instead of a single file
name.  These functions, openat etc, have been discussed on numerous
occasions.  They are needed to implement race-free filesystem traversal,
they are necessary to implement a virtual per-thread current working
directory (think multi-threaded backup software), etc.

We have in glibc today implementations of the interfaces which use the
/proc/self/fd magic.  But this code is rather expensive.  Here are some
results (similar to what Jim Meyering posted before).

The test creates a deep directory hierarchy on a tmpfs filesystem.  Then
rm -fr is used to remove all directories.  Without syscall support I get
this:

real    0m31.921s
user    0m0.688s
sys     0m31.234s

With syscall support the results are much better:

real    0m20.699s
user    0m0.536s
sys     0m20.149s

The interfaces are for obvious reasons currently not much used.  But they'll
be used.  coreutils (and Jeff's posixutils) are already using them.
Furthermore, code like ftw/fts in libc (maybe even glob) will also start using
them.  I expect a patch to make follow soon.  Every program which is walking
the filesystem tree will benefit.

Signed-off-by: Ulrich Drepper <drepper@redhat.com>
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@ftp.linux.org.uk>
Acked-by: Ingo Molnar <mingo@elte.hu>
Cc: Michael Kerrisk <mtk-manpages@gmx.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 136 insertions, 36 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 33fb5bd..4acdac0 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -30,6 +30,8 @@
 #include <linux/audit.h>
 #include <linux/capability.h>
 #include <linux/file.h>
+#include <linux/fcntl.h>
+#include <linux/namei.h>
 #include <asm/namei.h>
 #include <asm/uaccess.h>
 
@@ -1063,7 +1065,8 @@ set_it:
 }
 
 /* Returns 0 and nd will be valid on success; Retuns error, otherwise. */
-int fastcall path_lookup(const char *name, unsigned int flags, struct nameidata *nd)
+static int fastcall do_path_lookup(int dfd, const char *name,
+				unsigned int flags, struct nameidata *nd)
 {
 	int retval = 0;
 
@@ -1083,9 +1086,38 @@ int fastcall path_lookup(const char *name, unsigned int flags, struct nameidata
 		}
 		nd->mnt = mntget(current->fs->rootmnt);
 		nd->dentry = dget(current->fs->root);
-	} else {
+	} else if (dfd == AT_FDCWD) {
 		nd->mnt = mntget(current->fs->pwdmnt);
 		nd->dentry = dget(current->fs->pwd);
+	} else {
+		struct file *file;
+		int fput_needed;
+		struct dentry *dentry;
+
+		file = fget_light(dfd, &fput_needed);
+		if (!file) {
+			retval = -EBADF;
+			goto out_fail;
+		}
+
+		dentry = file->f_dentry;
+
+		if (!S_ISDIR(dentry->d_inode->i_mode)) {
+			retval = -ENOTDIR;
+			fput_light(file, fput_needed);
+			goto out_fail;
+		}
+
+		retval = file_permission(file, MAY_EXEC);
+		if (retval) {
+			fput_light(file, fput_needed);
+			goto out_fail;
+		}
+
+		nd->mnt = mntget(file->f_vfsmnt);
+		nd->dentry = dget(dentry);
+
+		fput_light(file, fput_needed);
 	}
 	read_unlock(&current->fs->lock);
 	current->total_link_count = 0;
@@ -1094,11 +1126,19 @@ out:
 	if (unlikely(current->audit_context
 		     && nd && nd->dentry && nd->dentry->d_inode))
 		audit_inode(name, nd->dentry->d_inode, flags);
+out_fail:
 	return retval;
 }
 
-static int __path_lookup_intent_open(const char *name, unsigned int lookup_flags,
-		struct nameidata *nd, int open_flags, int create_mode)
+int fastcall path_lookup(const char *name, unsigned int flags,
+			struct nameidata *nd)
+{
+	return do_path_lookup(AT_FDCWD, name, flags, nd);
+}
+
+static int __path_lookup_intent_open(int dfd, const char *name,
+		unsigned int lookup_flags, struct nameidata *nd,
+		int open_flags, int create_mode)
 {
 	struct file *filp = get_empty_filp();
 	int err;
@@ -1108,7 +1148,7 @@ static int __path_lookup_intent_open(const char *name, unsigned int lookup_flags
 	nd->intent.open.file = filp;
 	nd->intent.open.flags = open_flags;
 	nd->intent.open.create_mode = create_mode;
-	err = path_lookup(name, lookup_flags|LOOKUP_OPEN, nd);
+	err = do_path_lookup(dfd, name, lookup_flags|LOOKUP_OPEN, nd);
 	if (IS_ERR(nd->intent.open.file)) {
 		if (err == 0) {
 			err = PTR_ERR(nd->intent.open.file);
@@ -1126,10 +1166,10 @@ static int __path_lookup_intent_open(const char *name, unsigned int lookup_flags
  * @nd: pointer to nameidata
  * @open_flags: open intent flags
  */
-int path_lookup_open(const char *name, unsigned int lookup_flags,
+int path_lookup_open(int dfd, const char *name, unsigned int lookup_flags,
 		struct nameidata *nd, int open_flags)
 {
-	return __path_lookup_intent_open(name, lookup_flags, nd,
+	return __path_lookup_intent_open(dfd, name, lookup_flags, nd,
 			open_flags, 0);
 }
 
@@ -1141,12 +1181,12 @@ int path_lookup_open(const char *name, unsigned int lookup_flags,
  * @open_flags: open intent flags
  * @create_mode: create intent flags
  */
-static int path_lookup_create(const char *name, unsigned int lookup_flags,
-			      struct nameidata *nd, int open_flags,
-			      int create_mode)
+static int path_lookup_create(int dfd, const char *name,
+			      unsigned int lookup_flags, struct nameidata *nd,
+			      int open_flags, int create_mode)
 {
-	return __path_lookup_intent_open(name, lookup_flags|LOOKUP_CREATE, nd,
-			open_flags, create_mode);
+	return __path_lookup_intent_open(dfd, name, lookup_flags|LOOKUP_CREATE,
+			nd, open_flags, create_mode);
 }
 
 int __user_path_lookup_open(const char __user *name, unsigned int lookup_flags,
@@ -1156,7 +1196,7 @@ int __user_path_lookup_open(const char __user *name, unsigned int lookup_flags,
 	int err = PTR_ERR(tmp);
 
 	if (!IS_ERR(tmp)) {
-		err = __path_lookup_intent_open(tmp, lookup_flags, nd, open_flags, 0);
+		err = __path_lookup_intent_open(AT_FDCWD, tmp, lookup_flags, nd, open_flags, 0);
 		putname(tmp);
 	}
 	return err;
@@ -1248,18 +1288,24 @@ access:
  * that namei follows links, while lnamei does not.
  * SMP-safe
  */
-int fastcall __user_walk(const char __user *name, unsigned flags, struct nameidata *nd)
+int fastcall __user_walk_fd(int dfd, const char __user *name, unsigned flags,
+			    struct nameidata *nd)
 {
 	char *tmp = getname(name);
 	int err = PTR_ERR(tmp);
 
 	if (!IS_ERR(tmp)) {
-		err = path_lookup(tmp, flags, nd);
+		err = do_path_lookup(dfd, tmp, flags, nd);
 		putname(tmp);
 	}
 	return err;
 }
 
+int fastcall __user_walk(const char __user *name, unsigned flags, struct nameidata *nd)
+{
+	return __user_walk_fd(AT_FDCWD, name, flags, nd);
+}
+
 /*
  * It's inline, so penalty for filesystems that don't use sticky bit is
  * minimal.
@@ -1518,7 +1564,8 @@ int may_open(struct nameidata *nd, int acc_mode, int flag)
  * for symlinks (where the permissions are checked later).
  * SMP-safe
  */
-int open_namei(const char * pathname, int flag, int mode, struct nameidata *nd)
+int open_namei(int dfd, const char *pathname, int flag,
+		int mode, struct nameidata *nd)
 {
 	int acc_mode, error;
 	struct path path;
@@ -1540,7 +1587,8 @@ int open_namei(const char * pathname, int flag, int mode, struct nameidata *nd)
 	 * The simplest case - just a plain lookup.
 	 */
 	if (!(flag & O_CREAT)) {
-		error = path_lookup_open(pathname, lookup_flags(flag), nd, flag);
+		error = path_lookup_open(dfd, pathname, lookup_flags(flag),
+					 nd, flag);
 		if (error)
 			return error;
 		goto ok;
@@ -1549,7 +1597,7 @@ int open_namei(const char * pathname, int flag, int mode, struct nameidata *nd)
 	/*
 	 * Create - we need to know the parent.
 	 */
-	error = path_lookup_create(pathname, LOOKUP_PARENT, nd, flag, mode);
+	error = path_lookup_create(dfd,pathname,LOOKUP_PARENT,nd,flag,mode);
 	if (error)
 		return error;
 
@@ -1744,7 +1792,8 @@ int vfs_mknod(struct inode *dir, struct dentry *dentry, int mode, dev_t dev)
 	return error;
 }
 
-asmlinkage long sys_mknod(const char __user * filename, int mode, unsigned dev)
+asmlinkage long sys_mknodat(int dfd, const char __user *filename, int mode,
+				unsigned dev)
 {
 	int error = 0;
 	char * tmp;
@@ -1757,7 +1806,7 @@ asmlinkage long sys_mknod(const char __user * filename, int mode, unsigned dev)
 	if (IS_ERR(tmp))
 		return PTR_ERR(tmp);
 
-	error = path_lookup(tmp, LOOKUP_PARENT, &nd);
+	error = do_path_lookup(dfd, tmp, LOOKUP_PARENT, &nd);
 	if (error)
 		goto out;
 	dentry = lookup_create(&nd, 0);
@@ -1793,6 +1842,11 @@ out:
 	return error;
 }
 
+asmlinkage long sys_mknod(const char __user *filename, int mode, unsigned dev)
+{
+	return sys_mknodat(AT_FDCWD, filename, mode, dev);
+}
+
 int vfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
 {
 	int error = may_create(dir, dentry, NULL);
@@ -1815,7 +1869,7 @@ int vfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
 	return error;
 }
 
-asmlinkage long sys_mkdir(const char __user * pathname, int mode)
+asmlinkage long sys_mkdirat(int dfd, const char __user *pathname, int mode)
 {
 	int error = 0;
 	char * tmp;
@@ -1826,7 +1880,7 @@ asmlinkage long sys_mkdir(const char __user * pathname, int mode)
 		struct dentry *dentry;
 		struct nameidata nd;
 
-		error = path_lookup(tmp, LOOKUP_PARENT, &nd);
+		error = do_path_lookup(dfd, tmp, LOOKUP_PARENT, &nd);
 		if (error)
 			goto out;
 		dentry = lookup_create(&nd, 1);
@@ -1846,6 +1900,11 @@ out:
 	return error;
 }
 
+asmlinkage long sys_mkdir(const char __user *pathname, int mode)
+{
+	return sys_mkdirat(AT_FDCWD, pathname, mode);
+}
+
 /*
  * We try to drop the dentry early: we should have
  * a usage count of 2 if we're the only user of this
@@ -1907,7 +1966,7 @@ int vfs_rmdir(struct inode *dir, struct dentry *dentry)
 	return error;
 }
 
-asmlinkage long sys_rmdir(const char __user * pathname)
+static long do_rmdir(int dfd, const char __user *pathname)
 {
 	int error = 0;
 	char * name;
@@ -1918,7 +1977,7 @@ asmlinkage long sys_rmdir(const char __user * pathname)
 	if(IS_ERR(name))
 		return PTR_ERR(name);
 
-	error = path_lookup(name, LOOKUP_PARENT, &nd);
+	error = do_path_lookup(dfd, name, LOOKUP_PARENT, &nd);
 	if (error)
 		goto exit;
 
@@ -1948,6 +2007,11 @@ exit:
 	return error;
 }
 
+asmlinkage long sys_rmdir(const char __user *pathname)
+{
+	return do_rmdir(AT_FDCWD, pathname);
+}
+
 int vfs_unlink(struct inode *dir, struct dentry *dentry)
 {
 	int error = may_delete(dir, dentry, 0);
@@ -1984,7 +2048,7 @@ int vfs_unlink(struct inode *dir, struct dentry *dentry)
  * writeout happening, and we don't want to prevent access to the directory
  * while waiting on the I/O.
  */
-asmlinkage long sys_unlink(const char __user * pathname)
+static long do_unlinkat(int dfd, const char __user *pathname)
 {
 	int error = 0;
 	char * name;
@@ -1996,7 +2060,7 @@ asmlinkage long sys_unlink(const char __user * pathname)
 	if(IS_ERR(name))
 		return PTR_ERR(name);
 
-	error = path_lookup(name, LOOKUP_PARENT, &nd);
+	error = do_path_lookup(dfd, name, LOOKUP_PARENT, &nd);
 	if (error)
 		goto exit;
 	error = -EISDIR;
@@ -2031,6 +2095,22 @@ slashes:
 	goto exit2;
 }
 
+asmlinkage long sys_unlinkat(int dfd, const char __user *pathname, int flag)
+{
+	if ((flag & ~AT_REMOVEDIR) != 0)
+		return -EINVAL;
+
+	if (flag & AT_REMOVEDIR)
+		return do_rmdir(dfd, pathname);
+
+	return do_unlinkat(dfd, pathname);
+}
+
+asmlinkage long sys_unlink(const char __user *pathname)
+{
+	return do_unlinkat(AT_FDCWD, pathname);
+}
+
 int vfs_symlink(struct inode *dir, struct dentry *dentry, const char *oldname, int mode)
 {
 	int error = may_create(dir, dentry, NULL);
@@ -2052,7 +2132,8 @@ int vfs_symlink(struct inode *dir, struct dentry *dentry, const char *oldname, i
 	return error;
 }
 
-asmlinkage long sys_symlink(const char __user * oldname, const char __user * newname)
+asmlinkage long sys_symlinkat(const char __user *oldname,
+			      int newdfd, const char __user *newname)
 {
 	int error = 0;
 	char * from;
@@ -2067,7 +2148,7 @@ asmlinkage long sys_symlink(const char __user * oldname, const char __user * new
 		struct dentry *dentry;
 		struct nameidata nd;
 
-		error = path_lookup(to, LOOKUP_PARENT, &nd);
+		error = do_path_lookup(newdfd, to, LOOKUP_PARENT, &nd);
 		if (error)
 			goto out;
 		dentry = lookup_create(&nd, 0);
@@ -2085,6 +2166,11 @@ out:
 	return error;
 }
 
+asmlinkage long sys_symlink(const char __user *oldname, const char __user *newname)
+{
+	return sys_symlinkat(oldname, AT_FDCWD, newname);
+}
+
 int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_dentry)
 {
 	struct inode *inode = old_dentry->d_inode;
@@ -2132,7 +2218,8 @@ int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_de
  * with linux 2.0, and to avoid hard-linking to directories
  * and other special files.  --ADM
  */
-asmlinkage long sys_link(const char __user * oldname, const char __user * newname)
+asmlinkage long sys_linkat(int olddfd, const char __user *oldname,
+			   int newdfd, const char __user *newname)
 {
 	struct dentry *new_dentry;
 	struct nameidata nd, old_nd;
@@ -2143,10 +2230,10 @@ asmlinkage long sys_link(const char __user * oldname, const char __user * newnam
 	if (IS_ERR(to))
 		return PTR_ERR(to);
 
-	error = __user_walk(oldname, 0, &old_nd);
+	error = __user_walk_fd(olddfd, oldname, 0, &old_nd);
 	if (error)
 		goto exit;
-	error = path_lookup(to, LOOKUP_PARENT, &nd);
+	error = do_path_lookup(newdfd, to, LOOKUP_PARENT, &nd);
 	if (error)
 		goto out;
 	error = -EXDEV;
@@ -2169,6 +2256,11 @@ exit:
 	return error;
 }
 
+asmlinkage long sys_link(const char __user *oldname, const char __user *newname)
+{
+	return sys_linkat(AT_FDCWD, oldname, AT_FDCWD, newname);
+}
+
 /*
  * The worst of all namespace operations - renaming directory. "Perverted"
  * doesn't even start to describe it. Somebody in UCB had a heck of a trip...
@@ -2315,7 +2407,8 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 	return error;
 }
 
-static int do_rename(const char * oldname, const char * newname)
+static int do_rename(int olddfd, const char *oldname,
+			int newdfd, const char *newname)
 {
 	int error = 0;
 	struct dentry * old_dir, * new_dir;
@@ -2323,11 +2416,11 @@ static int do_rename(const char * oldname, const char * newname)
 	struct dentry * trap;
 	struct nameidata oldnd, newnd;
 
-	error = path_lookup(oldname, LOOKUP_PARENT, &oldnd);
+	error = do_path_lookup(olddfd, oldname, LOOKUP_PARENT, &oldnd);
 	if (error)
 		goto exit;
 
-	error = path_lookup(newname, LOOKUP_PARENT, &newnd);
+	error = do_path_lookup(newdfd, newname, LOOKUP_PARENT, &newnd);
 	if (error)
 		goto exit1;
 
@@ -2391,7 +2484,8 @@ exit:
 	return error;
 }
 
-asmlinkage long sys_rename(const char __user * oldname, const char __user * newname)
+asmlinkage long sys_renameat(int olddfd, const char __user *oldname,
+			     int newdfd, const char __user *newname)
 {
 	int error;
 	char * from;
@@ -2403,13 +2497,18 @@ asmlinkage long sys_rename(const char __user * oldname, const char __user * newn
 	to = getname(newname);
 	error = PTR_ERR(to);
 	if (!IS_ERR(to)) {
-		error = do_rename(from,to);
+		error = do_rename(olddfd, from, newdfd, to);
 		putname(to);
 	}
 	putname(from);
 	return error;
 }
 
+asmlinkage long sys_rename(const char __user *oldname, const char __user *newname)
+{
+	return sys_renameat(AT_FDCWD, oldname, AT_FDCWD, newname);
+}
+
 int vfs_readlink(struct dentry *dentry, char __user *buffer, int buflen, const char *link)
 {
 	int len;
@@ -2553,6 +2652,7 @@ struct inode_operations page_symlink_inode_operations = {
 };
 
 EXPORT_SYMBOL(__user_walk);
+EXPORT_SYMBOL(__user_walk_fd);
 EXPORT_SYMBOL(follow_down);
 EXPORT_SYMBOL(follow_up);
 EXPORT_SYMBOL(get_write_access); /* binfmt_aout */