# root is not show "." and ".\."
source code repo - [simplefs](https://github.com/sysprog21/simplefs)

## root directory do not show "." and ".\."

As we know the "." is a symbol link to currnet directory, and ".\." point to it's parent

When the file system is root for kernel system, the 'ls' do not show the =='.' / ".\."==, but if the file system is mounted to other file system, this file system's root should has '.' and ".\."

## test simplefs

test environmet:
1. ubuntu 5.15 run on ubuntu 22.04 with multipass emulator
2. UML 6.2 kernel using bz box

## test result
* ubuntu 5.15

ubuntu@primary:~/simplefs/test15$ ls -la
total 0

* UML 6.2 kernel

root@(none):/tmp/simplefs# ls -a
.    ..  (others hidden...)

## Root cause
By testing, it seems the glibc and bz box have different way to proecc the readdir, so let's read the source code:

* glibc readdir
[src here](https://elixir.bootlin.com/glibc/glibc-2.35.9000/source/sysdeps/unix/sysv/linux/readdir64.c#L31), glibc readdir seems skip the ino 0
* bz box readdir
[src here](https://github.com/mirror/busybox/blob/2d4a3d9e6c1493a9520b907e07a41aca90cdfd94/coreutils/ls.c#L924), bz box will read '.' and ".." for show

so by different lib, this has different way to show, but [ext2/ ext3/ ext4 file system don't use 0 for root inode](https://stackoverflow.com/questions/2099121/why-do-inode-numbers-start-from-1-and-not-0), and linux kernel doc. also suggest that the inode should not be 0 - ["There is no inode 0"](https://www.kernel.org/doc/html/latest/filesystems/ext4/inodes.html?highlight=inode)

vfs also avoid the inode number 0 in [RFC](https://patchwork.kernel.org/project/linux-fsdevel/patch/[e-mail]/)

so solution is very easy

     }

     /* Create root inode */
-    root_inode = simplefs_iget(sb, 0);
+    root_inode = simplefs_iget(sb, 1);
     if (IS_ERR(root_inode)) {
         ret = PTR_ERR(root_inode);
         goto free_bfree;

## commit log:
following is commit log

Fix fs not showing current and parent directories

### Description
-----------
In previous linux kernel version (e.g 5.8), ls -la will not show . and .. in root directory

### Root cause
----------
In Linux system, there are different way to implement "ls" command. Like Ubuntu system, using glibc. Embedded system using busybox, [glibc](https://elixir.bootlin.com/glibc/glibc-2.35.9000/source/sysdeps/unix/sysv/linux/readdir64.c#L31)/ [busybox](https://github.com/mirror/busybox/blob/2d4a3d9e6c1493a9520b907e07a41aca90cdfd94/coreutils/ls.c#L924)

And you can see that the ext2/ ext3/ ext4/ system all [skip inode number 0](https://stackoverflow.com/questions/2099121/why-do-inode-numbers-start-from-1-and-not-0)

In kernel document [ext4](https://www.kernel.org/doc/html/latest/filesystems/ext4/inodes.html?highlight=inode) also say that "There is no inode 0"

And [patchwork - vfs: avoid creation of inode number 0 in get_next_ino](https://patchwork.kernel.org/project/linux-fsdevel/patch/[e-mail]/) add code to avoid to provide the 0 inode so in [6.3 kernel](https://elixir.bootlin.com/linux/v6.3.13/source/fs/inode.c#L983) src code, we can see these patch code

### Fix solution
----------
By following ext4 rule, skip inode number 0. When creating image layout in inode section, we skip first block and use next inode ( inode number 1 ) with the root inode.

And we also modify the d_make_root, we use inode number 1 for the root inode.

### How has this been tested?
----------
In kernel 5.15 here is original source code

ubuntu@primary:/home/roy/src-code/github/roy/simplefs/test15$ uname -a
Linux primary 5.15.0-73-generic #80-Ubuntu SMP Mon May 15 15:18:26 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux
ubuntu@primary:/home/roy/src-code/github/roy/simplefs/test15$ ls -la
total 0

In kernel 5.15 here is patch code

ubuntu@primary:/home/roy/src-code/github/roy/simplefs/test15$ uname -a
Linux primary 5.15.0-73-generic #80-Ubuntu SMP Mon May 15 15:18:26 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux
ubuntu@primary:/home/roy/src-code/github/roy/simplefs/test15$ ls -la
total 5
drwxrwxr-x 2 root   root   4096 Jan  1  1970 .
drwxrwxr-x 1 ubuntu ubuntu 4096 Jul 22 22:10 ..

In kernel 5.4 here is original source code

ubuntu@vcluster101-vxm:/home/roy/src-code/github/roy/simplefs$ uname -a
Linux vcluster101-vxm 5.4.0-153-generic #170-Ubuntu SMP Fri Jun 16 13:43:31 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux
ubuntu@vcluster101-vxm:/home/roy/src-code/github/roy/simplefs/test4$ ls -la
total 0

In kernel 5.4 here is patch code

buntu@vcluster101-vxm:/home/roy/src-code/github/roy/simplefs/test4$ ls -la
total 5
drwxrwxr-x 2 root   root   4096 Jan  1  1970 .
drwxrwxr-x 1 ubuntu ubuntu 4096 Jul 22 22:42 ..
ubuntu@vcluster101-vxm:/home/roy/src-code/github/roy/simplefs/test4$ uname -a
Linux vcluster101-vxm 5.4.0-153-generic #170-Ubuntu SMP Fri Jun 16 13:43:31 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux

### references
---------
[glibc](https://sourceware.org/bugzilla/show_bug.cgi?id=19970) may have a patch to fix readdir?