linux-kernel - Re: [PATCH v8 04/20] cachefiles: notify user daemon when withdrawing cookie

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Date:   Tue, 12 Apr 2022 11:35:51 +0800
From:   JeffleXu <jefflexu@...ux.alibaba.com>
To:     David Howells <dhowells@...hat.com>
Cc:     linux-cachefs@...hat.com, xiang@...nel.org, chao@...nel.org,
        linux-erofs@...ts.ozlabs.org, torvalds@...ux-foundation.org,
        gregkh@...uxfoundation.org, willy@...radead.org,
        linux-fsdevel@...r.kernel.org, joseph.qi@...ux.alibaba.com,
        bo.liu@...ux.alibaba.com, tao.peng@...ux.alibaba.com,
        gerry@...ux.alibaba.com, eguan@...ux.alibaba.com,
        linux-kernel@...r.kernel.org, luodaowen.backend@...edance.com,
        tianzichen@...ishou.com, fannaihao@...du.com
Subject: Re: [PATCH v8 04/20] cachefiles: notify user daemon when withdrawing
 cookie



On 4/11/22 9:42 PM, David Howells wrote:
> JeffleXu <jefflexu@...ux.alibaba.com> wrote:
> 
>>>
>>>> +	if (fd == 0)
>>>> +		return -ENOENT;
>>>
>>> 0 is a valid fd.
>>
>> Yeah, but IMHO fd 0 is always for stdin? I think the allocated anon_fd
>> won't install at fd 0. Please correct me if I'm wrong.
> 
> If someone has closed 0, then you'll get 0 next, I'm pretty sure.  Try it and
> see.

Good catch.

> 
>> In fact I wanna use "fd == 0" as the initial state as struct
>> cachefiles_object is allocated with kmem_cache_zalloc().
> 
> I would suggest presetting it to something like -2 to avoid confusion.

Okay, as described in the previous email, I'm going to replace @fd to
@object_id. I will define some symbols to make it more readable,
something like

```
struct cachefiles_object {
	...
#ifdef CONFIG_CACHEFILES_ONDEMAND
#define CACHEFILES_OBJECT_ID_DEFAULT -2
#define CACHEFILES_OBJECT_ID_DEAD    -1
	int object_id;
#endif
	...
}
```

Thanks for your time.

-- 
Thanks,
Jeffle