Re: [PATCH] Fix EROFS Kconfig

Jingbo Xu
2023-12-23T03:55:13Z

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