give readdir(2)/getdents(2)/etc. uniform exclusion with lseek()

same as read() on regular files has, and for the same reason.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/readdir.c

@@ -112,7 +112,7 @@ SYSCALL_DEFINE3(old_readdir, unsigned int, fd,
 		struct old_linux_dirent __user *, dirent, unsigned int, count)
 {
 	int error;
-	struct fd f = fdget(fd);
+	struct fd f = fdget_pos(fd);
 	struct readdir_callback buf = {
 		.ctx.actor = fillonedir,
 		.dirent = dirent
@@ -125,7 +125,7 @@ SYSCALL_DEFINE3(old_readdir, unsigned int, fd,
 	if (buf.result)
 		error = buf.result;
 
-	fdput(f);
+	fdput_pos(f);
 	return error;
 }
 
@@ -209,7 +209,7 @@ SYSCALL_DEFINE3(getdents, unsigned int, fd,
 	if (!access_ok(VERIFY_WRITE, dirent, count))
 		return -EFAULT;
 
-	f = fdget(fd);
+	f = fdget_pos(fd);
 	if (!f.file)
 		return -EBADF;
 
@@ -223,7 +223,7 @@ SYSCALL_DEFINE3(getdents, unsigned int, fd,
 		else
 			error = count - buf.count;
 	}
-	fdput(f);
+	fdput_pos(f);
 	return error;
 }
 
@@ -290,7 +290,7 @@ SYSCALL_DEFINE3(getdents64, unsigned int, fd,
 	if (!access_ok(VERIFY_WRITE, dirent, count))
 		return -EFAULT;
 
-	f = fdget(fd);
+	f = fdget_pos(fd);
 	if (!f.file)
 		return -EBADF;
 
@@ -305,6 +305,6 @@ SYSCALL_DEFINE3(getdents64, unsigned int, fd,
 		else
 			error = count - buf.count;
 	}
-	fdput(f);
+	fdput_pos(f);
 	return error;
 }