[PATCH 2/2] cachefiles: support query cachefiles ondemand feature

[Hongbo Li]

On 2024/6/21 17:14, Gao Xiang wrote:
> 
> 
> On 2024/6/21 14:18, Hongbo Li wrote:
>> Erofs over fscache need CONFIG_CACHEFILES_ONDEMAND in cachefiles
>> module. We cannot know whether it is supported from userspace, so
>> we export this feature to user by sysfs interface.
>>
>> [Before]
>> $ cat /sys/fs/cachefiles/features/cachefiles_ondemand
>> cat: /sys/fs/cachefiles/features/cachefiles_ondemand: No such file or 
>> directory
>>
>> [After]
>> $ cat /sys/fs/cachefiles/features/cachefiles_ondemand
>> supported
>>
>> Signed-off-by: Hongbo Li <lihongbo22 at huawei.com>
> 
> I don't think such sysfs is needed, you could just use
> `bind ondemand` to check if it is supported:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/cachefiles/daemon.c?h=v6.9#n780
> 
Thanks for reply!
`bind ondemand` can check if it is supported, but it requires a more 
complicated procedure for user to implement. For example, a serial of 
system call (open, ioctl, close) are need.The containerd snapshotter 
daemon relies on these feature, only use a simple check method is usable 
in product environment. The snapshotter developers may know how 
cachefiles works, but for snapshotter users, a simple way to check 
whether snapshotter can be launched is useful. Even though they do not 
know how cachefiles works.

Thanks,
Hongbo
> 
> Thanks,
> Gao Xiang