Re: [PATCH] Fix EROFS Kconfig

From: Jingbo Xu <jefflexu@linux.alibaba.com>
To: David Howells <dhowells@redhat.com>, Gao Xiang <xiang@kernel.org>
Cc: Chao Yu <chao@kernel.org>, Yue Hu <huyue2@coolpad.com>,
	Steve French <smfrench@gmail.com>,
	Matthew Wilcox <willy@infradead.org>,
	Marc Dionne <marc.dionne@auristor.com>,
	Paulo Alcantara <pc@manguebit.com>,
	Shyam Prasad N <sprasad@microsoft.com>,
	Tom Talpey <tom@talpey.com>,
	Dominique Martinet <asmadeus@codewreck.org>,
	Eric Van Hensbergen <ericvh@kernel.org>,
	Ilya Dryomov <idryomov@gmail.com>,
	Christian Brauner <christian@brauner.io>,
	linux-cachefs@redhat.com, linux-afs@lists.infradead.org,
	linux-cifs@vger.kernel.org, linux-nfs@vger.kernel.org,
	ceph-devel@vger.kernel.org, v9fs@lists.linux.dev,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-erofs@lists.ozlabs.org, Jeff Layton <jlayton@kernel.org>
Subject: Re: [PATCH] Fix EROFS Kconfig
Date: Sat, 23 Dec 2023 11:55:00 +0800	[thread overview]
Message-ID: <d50555e9-3b8e-41d4-bec6-317aaaec5ff0@linux.alibaba.com> (raw)
In-Reply-To: <2265065.1703250126@warthog.procyon.org.uk>

Hi,

On 12/22/23 9:02 PM, David Howells wrote:
> This needs an additional change (see attached).
> 
> diff --git a/fs/erofs/Kconfig b/fs/erofs/Kconfig
> index 1d318f85232d..1949763e66aa 100644
> --- a/fs/erofs/Kconfig
> +++ b/fs/erofs/Kconfig
> @@ -114,7 +114,8 @@ config EROFS_FS_ZIP_DEFLATE
>  
>  config EROFS_FS_ONDEMAND
>  	bool "EROFS fscache-based on-demand read support"
> -	depends on CACHEFILES_ONDEMAND && (EROFS_FS=m && FSCACHE || EROFS_FS=y && FSCACHE=y)
> +	depends on CACHEFILES_ONDEMAND && FSCACHE && \
> +		(EROFS_FS=m && NETFS_SUPPORT || EROFS_FS=y && NETFS_SUPPORT=y)
>  	default n
>  	help
>  	  This permits EROFS to use fscache-backed data blobs with on-demand
> 

Thanks for the special reminder.  I noticed that it has been included in
this commit[*] in the dev tree.

[*]
https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/commit/?h=netfs-lib&id=7472173cc3baf4a0bd8c803e56c37efdb8388f1c


Besides I noticed an issue when trying to configure EROFS_FS_ONDEMAND.
The above kconfig indicates that EROFS_FS_ONDEMAND depends on
NETFS_SUPPORT, while NETFS_SUPPORT has no prompt in menuconfig and can
only be selected by, e.g. fs/ceph/Kconfig:

	config CEPH_FS
        select NETFS_SUPPORT

IOW EROFS_FS_ONDEMAND will not be prompted and has no way being
configured if NETFS_SUPPORT itself is not selected by any other filesystem.


I tried to fix this in following way:

diff --git a/fs/erofs/Kconfig b/fs/erofs/Kconfig
index 1949763e66aa..5b7b71e537f1 100644
--- a/fs/erofs/Kconfig
+++ b/fs/erofs/Kconfig
@@ -5,6 +5,7 @@ config EROFS_FS
        depends on BLOCK
        select FS_IOMAP
        select LIBCRC32C
+       select NETFS_SUPPORT if EROFS_FS_ONDEMAND
        help
          EROFS (Enhanced Read-Only File System) is a lightweight read-only
          file system with modern designs (e.g. no buffer heads, inline
@@ -114,8 +115,10 @@ config EROFS_FS_ZIP_DEFLATE

 config EROFS_FS_ONDEMAND
        bool "EROFS fscache-based on-demand read support"
-       depends on CACHEFILES_ONDEMAND && FSCACHE && \
-               (EROFS_FS=m && NETFS_SUPPORT || EROFS_FS=y &&
NETFS_SUPPORT=y)
+       depends on EROFS_FS
+       select FSCACHE
        default n
        help
          This permits EROFS to use fscache-backed data blobs with on-demand


But still the dependency for CACHEFILES_ONDEMAND and CACHEFILES can not
be resolved.  Though CACHEFILES is not a must during the linking stage
as EROFS only calls fscache APIs directly, CACHEFILES is indeed needed
to ensure that the EROFS on-demand functionality works at runtime.

If we let EROFS_FS_ONDEMAND select CACHEFILES_ONDEMAND, then only
CACHEFILES_ONDEMAND will be selected while CACHEFILES can be still N.
Maybe EROFS_FS_ONDEMAND needs to selct both CACHEFILES_ONDEMAND and
CACHEFILES?

Besides if we make EROFS_FS_ONDEMAND depends on CACHEFILES_ONDEMAND,
then there will be a recursive dependency loop, as

fs/netfs/Kconfig:3:error: recursive dependency detected!
fs/netfs/Kconfig:3:	symbol NETFS_SUPPORT is selected by EROFS_FS_ONDEMAND
fs/erofs/Kconfig:116:	symbol EROFS_FS_ONDEMAND depends on
CACHEFILES_ONDEMAND
fs/cachefiles/Kconfig:30:	symbol CACHEFILES_ONDEMAND depends on CACHEFILES
fs/cachefiles/Kconfig:3:	symbol CACHEFILES depends on NETFS_SUPPORT


Hi Xiang, any better idea?



-- 
Thanks,
Jingbo
