linux-kernel - Re: [PATCH 3/3] init/do_mounts.c: fix rootfs_fs

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Message-ID: <20210525005256.GF4332@42.do-not-panic.com>
Date:   Tue, 25 May 2021 00:52:56 +0000
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     menglong8.dong@...il.com
Cc:     viro@...iv.linux.org.uk, keescook@...omium.org,
        samitolvanen@...gle.com, johan@...nel.org, ojeda@...nel.org,
        jeyu@...nel.org, joe@...ches.com, dong.menglong@....com.cn,
        masahiroy@...nel.org, jack@...e.cz, axboe@...nel.dk, hare@...e.de,
        gregkh@...uxfoundation.org, tj@...nel.org, song@...nel.org,
        neilb@...e.de, akpm@...ux-foundation.org, brho@...gle.com,
        f.fainelli@...il.com, wangkefeng.wang@...wei.com, arnd@...db.de,
        linux@...musvillemoes.dk, mhiramat@...nel.org, rostedt@...dmis.org,
        vbabka@...e.cz, glider@...gle.com, pmladek@...e.com,
        ebiederm@...ssion.com, jojing64@...il.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Josh Triplett <josh@...htriplett.org>
Subject: Re: [PATCH 3/3] init/do_mounts.c: fix rootfs_fs_type with ramfs

On Sat, May 22, 2021 at 07:31:55PM +0800, menglong8.dong@...il.com wrote:
> From: Menglong Dong <dong.menglong@....com.cn>
> 
> As for the existence of 'user root' which is introduced in previous
> patch, 'rootfs_fs_type', which is used as the root of mount tree,
> is not used directly any more. So it make no sense to switch it
> between ramfs and tmpfs, just fix it with ramfs to simplify the
> code.

You also noted this could be arbitrary. I don't see why its true that
the context used for init_mount_tree() can be arbitrary. And if it can
be, then why remove it / replace it with something more NULL like?

  Luis

> Signed-off-by: Menglong Dong <dong.menglong@....com.cn>
> ---
>  fs/namespace.c       |  2 --
>  include/linux/init.h |  1 -
>  init/do_mounts.c     | 18 +-----------------
>  3 files changed, 1 insertion(+), 20 deletions(-)
> 
> diff --git a/fs/namespace.c b/fs/namespace.c
> index f63337828e1c..8d2b57938e3a 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -17,7 +17,6 @@
>  #include <linux/security.h>
>  #include <linux/cred.h>
>  #include <linux/idr.h>
> -#include <linux/init.h>		/* init_rootfs */
>  #include <linux/fs_struct.h>	/* get_fs_root et.al. */
>  #include <linux/fsnotify.h>	/* fsnotify_vfsmount_delete */
>  #include <linux/file.h>
> @@ -4241,7 +4240,6 @@ void __init mnt_init(void)
>  	if (!fs_kobj)
>  		printk(KERN_WARNING "%s: kobj create error\n", __func__);
>  	shmem_init();
> -	init_rootfs();
>  	init_mount_tree();
>  }
>  
> diff --git a/include/linux/init.h b/include/linux/init.h
> index 045ad1650ed1..86bd92bb9550 100644
> --- a/include/linux/init.h
> +++ b/include/linux/init.h
> @@ -148,7 +148,6 @@ extern unsigned int reset_devices;
>  /* used by init/main.c */
>  void setup_arch(char **);
>  void prepare_namespace(void);
> -void __init init_rootfs(void);
>  extern struct file_system_type rootfs_fs_type;
>  
>  #if defined(CONFIG_STRICT_KERNEL_RWX) || defined(CONFIG_STRICT_MODULE_RWX)
> diff --git a/init/do_mounts.c b/init/do_mounts.c
> index 943cb58846fb..6d1253f75bb0 100644
> --- a/init/do_mounts.c
> +++ b/init/do_mounts.c
> @@ -689,24 +689,8 @@ void __init init_user_rootfs(void)
>  	}
>  }
>  
> -static bool is_tmpfs;
> -static int rootfs_init_fs_context(struct fs_context *fc)
> -{
> -	if (IS_ENABLED(CONFIG_TMPFS) && is_tmpfs)
> -		return shmem_init_fs_context(fc);
> -
> -	return ramfs_init_fs_context(fc);
> -}
> -
>  struct file_system_type rootfs_fs_type = {
>  	.name		= "rootfs",
> -	.init_fs_context = rootfs_init_fs_context,
> +	.init_fs_context = ramfs_init_fs_context,
>  	.kill_sb	= kill_litter_super,
>  };

You mentioned 
> -
> -void __init init_rootfs(void)
> -{
> -	if (IS_ENABLED(CONFIG_TMPFS) && !saved_root_name[0] &&
> -		(!root_fs_names || strstr(root_fs_names, "tmpfs")))
> -		is_tmpfs = true;
> -}
> -- 
> 2.31.1
>