vfs: Deduplicate code shared by xattr system calls operating on paths

The following pairs of system calls dealing with extended attributes only
differ in their behavior on whether the symbolic link is followed (when
the named file is a symbolic link):

- setxattr() and lsetxattr()
- getxattr() and lgetxattr()
- listxattr() and llistxattr()
- removexattr() and lremovexattr()

Despite this, the implementations all had duplicated code, so this commit
redirects each of the above pairs of system calls to a corresponding
function to which different lookup flags (LOOKUP_FOLLOW or 0) are passed.

For me this reduced the stripped size of xattr.o from 8824 to 8248 bytes.
Signed-off-by: Eric Biggers <ebiggers3@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/xattr.c

@@ -364,13 +364,12 @@ setxattr(struct dentry *d, const char __user *name, const void __user *value,
 	return error;
 }
 
-SYSCALL_DEFINE5(setxattr, const char __user *, pathname,
-		const char __user *, name, const void __user *, value,
-		size_t, size, int, flags)
+static int path_setxattr(const char __user *pathname,
+			 const char __user *name, const void __user *value,
+			 size_t size, int flags, unsigned int lookup_flags)
 {
 	struct path path;
 	int error;
-	unsigned int lookup_flags = LOOKUP_FOLLOW;
 retry:
 	error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
 	if (error)
@@ -388,28 +387,18 @@ SYSCALL_DEFINE5(setxattr, const char __user *, pathname,
 	return error;
 }
 
+SYSCALL_DEFINE5(setxattr, const char __user *, pathname,
+		const char __user *, name, const void __user *, value,
+		size_t, size, int, flags)
+{
+	return path_setxattr(pathname, name, value, size, flags, LOOKUP_FOLLOW);
+}
+
 SYSCALL_DEFINE5(lsetxattr, const char __user *, pathname,
 		const char __user *, name, const void __user *, value,
 		size_t, size, int, flags)
 {
-	struct path path;
-	int error;
-	unsigned int lookup_flags = 0;
-retry:
-	error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
-	if (error)
-		return error;
-	error = mnt_want_write(path.mnt);
-	if (!error) {
-		error = setxattr(path.dentry, name, value, size, flags);
-		mnt_drop_write(path.mnt);
-	}
-	path_put(&path);
-	if (retry_estale(error, lookup_flags)) {
-		lookup_flags |= LOOKUP_REVAL;
-		goto retry;
-	}
-	return error;
+	return path_setxattr(pathname, name, value, size, flags, 0);
 }
 
 SYSCALL_DEFINE5(fsetxattr, int, fd, const char __user *, name,
@@ -481,12 +470,12 @@ getxattr(struct dentry *d, const char __user *name, void __user *value,
 	return error;
 }
 
-SYSCALL_DEFINE4(getxattr, const char __user *, pathname,
-		const char __user *, name, void __user *, value, size_t, size)
+static ssize_t path_getxattr(const char __user *pathname,
+			     const char __user *name, void __user *value,
+			     size_t size, unsigned int lookup_flags)
 {
 	struct path path;
 	ssize_t error;
-	unsigned int lookup_flags = LOOKUP_FOLLOW;
 retry:
 	error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
 	if (error)
@@ -500,23 +489,16 @@ SYSCALL_DEFINE4(getxattr, const char __user *, pathname,
 	return error;
 }
 
+SYSCALL_DEFINE4(getxattr, const char __user *, pathname,
+		const char __user *, name, void __user *, value, size_t, size)
+{
+	return path_getxattr(pathname, name, value, size, LOOKUP_FOLLOW);
+}
+
 SYSCALL_DEFINE4(lgetxattr, const char __user *, pathname,
 		const char __user *, name, void __user *, value, size_t, size)
 {
-	struct path path;
-	ssize_t error;
-	unsigned int lookup_flags = 0;
-retry:
-	error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
-	if (error)
-		return error;
-	error = getxattr(path.dentry, name, value, size);
-	path_put(&path);
-	if (retry_estale(error, lookup_flags)) {
-		lookup_flags |= LOOKUP_REVAL;
-		goto retry;
-	}
-	return error;
+	return path_getxattr(pathname, name, value, size, 0);
 }
 
 SYSCALL_DEFINE4(fgetxattr, int, fd, const char __user *, name,
@@ -571,12 +553,11 @@ listxattr(struct dentry *d, char __user *list, size_t size)
 	return error;
 }
 
-SYSCALL_DEFINE3(listxattr, const char __user *, pathname, char __user *, list,
-		size_t, size)
+static ssize_t path_listxattr(const char __user *pathname, char __user *list,
+			      size_t size, unsigned int lookup_flags)
 {
 	struct path path;
 	ssize_t error;
-	unsigned int lookup_flags = LOOKUP_FOLLOW;
 retry:
 	error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
 	if (error)
@@ -590,23 +571,16 @@ SYSCALL_DEFINE3(listxattr, const char __user *, pathname, char __user *, list,
 	return error;
 }
 
+SYSCALL_DEFINE3(listxattr, const char __user *, pathname, char __user *, list,
+		size_t, size)
+{
+	return path_listxattr(pathname, list, size, LOOKUP_FOLLOW);
+}
+
 SYSCALL_DEFINE3(llistxattr, const char __user *, pathname, char __user *, list,
 		size_t, size)
 {
-	struct path path;
-	ssize_t error;
-	unsigned int lookup_flags = 0;
-retry:
-	error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
-	if (error)
-		return error;
-	error = listxattr(path.dentry, list, size);
-	path_put(&path);
-	if (retry_estale(error, lookup_flags)) {
-		lookup_flags |= LOOKUP_REVAL;
-		goto retry;
-	}
-	return error;
+	return path_listxattr(pathname, list, size, 0);
 }
 
 SYSCALL_DEFINE3(flistxattr, int, fd, char __user *, list, size_t, size)
@@ -640,12 +614,11 @@ removexattr(struct dentry *d, const char __user *name)
 	return vfs_removexattr(d, kname);
 }
 
-SYSCALL_DEFINE2(removexattr, const char __user *, pathname,
-		const char __user *, name)
+static int path_removexattr(const char __user *pathname,
+			    const char __user *name, unsigned int lookup_flags)
 {
 	struct path path;
 	int error;
-	unsigned int lookup_flags = LOOKUP_FOLLOW;
 retry:
 	error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
 	if (error)
@@ -663,27 +636,16 @@ SYSCALL_DEFINE2(removexattr, const char __user *, pathname,
 	return error;
 }
 
+SYSCALL_DEFINE2(removexattr, const char __user *, pathname,
+		const char __user *, name)
+{
+	return path_removexattr(pathname, name, LOOKUP_FOLLOW);
+}
+
 SYSCALL_DEFINE2(lremovexattr, const char __user *, pathname,
 		const char __user *, name)
 {
-	struct path path;
-	int error;
-	unsigned int lookup_flags = 0;
-retry:
-	error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
-	if (error)
-		return error;
-	error = mnt_want_write(path.mnt);
-	if (!error) {
-		error = removexattr(path.dentry, name);
-		mnt_drop_write(path.mnt);
-	}
-	path_put(&path);
-	if (retry_estale(error, lookup_flags)) {
-		lookup_flags |= LOOKUP_REVAL;
-		goto retry;
-	}
-	return error;
+	return path_removexattr(pathname, name, 0);
 }
 
 SYSCALL_DEFINE2(fremovexattr, int, fd, const char __user *, name)