fs: split off vfs_getdents function of getdents64 syscall

This splits off the vfs_getdents function from the getdents64 system
call. This allows io_uring to call the function.

Signed-off-by: Stefan Roesch <shr@fb.com>

fs/internal.h

@@ -194,3 +194,11 @@ long splice_file_to_pipe(struct file *in,
 			 struct pipe_inode_info *opipe,
 			 loff_t *offset,
 			 size_t len, unsigned int flags);
+
+/*
+ * fs/readdir.c
+ */
+struct linux_dirent64;
+
+int vfs_getdents(struct file *file, struct linux_dirent64 __user *dirent,
+		 unsigned int count, s64 pos);

fs/readdir.c

@@ -368,22 +368,26 @@ static int filldir64(struct dir_context *ctx, const char *name, int namlen,
 	return -EFAULT;
 }
 
-SYSCALL_DEFINE3(getdents64, unsigned int, fd,
-		struct linux_dirent64 __user *, dirent, unsigned int, count)
+/**
+ * vfs_getdents - getdents without fdget
+ * @file    : pointer to file struct of directory
+ * @dirent  : pointer to user directory structure
+ * @count   : size of buffer
+ * @ctx_pos : if file pos is used, pass -1,
+ *            if ctx pos is used, pass ctx pos
+ */
+int vfs_getdents(struct file *file, struct linux_dirent64 __user *dirent,
+		 unsigned int count, s64 ctx_pos)
 {
-	struct fd f;
 	struct getdents_callback64 buf = {
 		.ctx.actor = filldir64,
+		.ctx.pos = ctx_pos,
 		.count = count,
 		.current_dir = dirent
 	};
 	int error;
 
-	f = fdget_pos(fd);
-	if (!f.file)
-		return -EBADF;
-
-	error = iterate_dir(f.file, &buf.ctx);
+	error = do_iterate_dir(file, &buf.ctx, ctx_pos < 0);
 	if (error >= 0)
 		error = buf.error;
 	if (buf.prev_reclen) {
@@ -396,6 +400,22 @@ SYSCALL_DEFINE3(getdents64, unsigned int, fd,
 		else
 			error = count - buf.count;
 	}
+
+	return error;
+}
+
+SYSCALL_DEFINE3(getdents64, unsigned int, fd,
+		struct linux_dirent64 __user *, dirent, unsigned int, count)
+{
+	struct fd f;
+	int error;
+
+	f = fdget_pos(fd);
+	if (!f.file)
+		return -EBADF;
+
+	error = vfs_getdents(f.file, dirent, count, -1);
+
 	fdput_pos(f);
 	return error;
 }