linux-kernel - Re: [PATCH 1/2] erofs: simplify instantiation of pseudo mount in fscache mode

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Message-ID: <57f8d2a3-e00c-d281-708a-f1eb66257c69@linux.alibaba.com>
Date:   Fri, 3 Feb 2023 15:14:01 +0800
From:   Gao Xiang <hsiangkao@...ux.alibaba.com>
To:     Jingbo Xu <jefflexu@...ux.alibaba.com>, xiang@...nel.org,
        chao@...nel.org, linux-erofs@...ts.ozlabs.org,
        zhujia.zj@...edance.com, houtao1@...wei.com
Cc:     huyue2@...lpad.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] erofs: simplify instantiation of pseudo mount in
 fscache mode



On 2023/2/3 11:47, Jingbo Xu wrote:
> Introduce a pseudo fs type dedicated to the pseudo mount of fscache
> mode, so that the logic of real mount won't be messed up with that of
> pseudo mount, making the implementation of fscache mode more
> self-contained.
> 
> Signed-off-by: Jingbo Xu <jefflexu@...ux.alibaba.com>
> ---
>   fs/erofs/fscache.c  | 46 +++++++++++++++++++++++++++------------------
>   fs/erofs/internal.h |  6 ++++++
>   fs/erofs/super.c    | 35 +++++++---------------------------
>   3 files changed, 41 insertions(+), 46 deletions(-)
> 
> diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
> index af6ba52bbe8b..2eb42bbc56a4 100644
> --- a/fs/erofs/fscache.c
> +++ b/fs/erofs/fscache.c
> @@ -6,12 +6,13 @@
>   #include <linux/fscache.h>
>   #include <linux/file.h>
>   #include <linux/anon_inodes.h>
> +#include <linux/pseudo_fs.h>
>   #include "internal.h"
>   
>   static DEFINE_MUTEX(erofs_domain_list_lock);
>   static DEFINE_MUTEX(erofs_domain_cookies_lock);
>   static LIST_HEAD(erofs_domain_list);
> -static struct vfsmount *erofs_pseudo_mnt;
> +static struct vfsmount *erofs_pseudo_mnt __read_mostly;
>   
>   struct erofs_fscache_request {
>   	struct erofs_fscache_request *primary;
> @@ -471,10 +472,6 @@ static void erofs_fscache_domain_put(struct erofs_domain *domain)
>   	mutex_lock(&erofs_domain_list_lock);
>   	if (refcount_dec_and_test(&domain->ref)) {
>   		list_del(&domain->list);
> -		if (list_empty(&erofs_domain_list)) {
> -			kern_unmount(erofs_pseudo_mnt);
> -			erofs_pseudo_mnt = NULL;
> -		}
>   		mutex_unlock(&erofs_domain_list_lock);
>   		fscache_relinquish_volume(domain->volume, NULL, false);
>   		kfree(domain->domain_id);
> @@ -526,15 +523,10 @@ static int erofs_fscache_init_domain(struct super_block *sb)
>   	}
>   
>   	err = erofs_fscache_register_volume(sb);
> -	if (err)
> -		goto out;
> -
> -	if (!erofs_pseudo_mnt) {
> -		erofs_pseudo_mnt = kern_mount(&erofs_fs_type);
> -		if (IS_ERR(erofs_pseudo_mnt)) {
> -			err = PTR_ERR(erofs_pseudo_mnt);
> -			goto out;
> -		}
> +	if (err) {
> +		kfree(domain->domain_id);
> +		kfree(domain);
> +		return err;
>   	}
>   
>   	domain->volume = sbi->volume;
> @@ -542,10 +534,6 @@ static int erofs_fscache_init_domain(struct super_block *sb)
>   	list_add(&domain->list, &erofs_domain_list);
>   	sbi->domain = domain;
>   	return 0;
> -out:
> -	kfree(domain->domain_id);
> -	kfree(domain);
> -	return err;
>   }
>   
>   static int erofs_fscache_register_domain(struct super_block *sb)
> @@ -780,3 +768,25 @@ void erofs_fscache_unregister_fs(struct super_block *sb)
>   	sbi->volume = NULL;
>   	sbi->domain = NULL;
>   }
> +
> +static int erofs_fc_anon_get_tree(struct fs_context *fc)
> +{
> +	return PTR_ERR_OR_ZERO(init_pseudo(fc, EROFS_SUPER_MAGIC));
> +}
> +
> +int __init erofs_fscache_init(void)
> +{
> +	static struct file_system_type erofs_anon_fs = {
> +		.name		= "erofs_anonfs",
> +		.init_fs_context = erofs_fc_anon_get_tree,
> +		.kill_sb	= kill_anon_super,
> +	};


Please don't add another filesystem type, thanks.

Thanks,
Gao Xiang