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Message-ID: <a20ca50f-1d1a-d09e-75da-f6ced65f6c93@linux.alibaba.com>
Date:   Tue, 12 Apr 2022 11:35:51 +0800
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Subject: Re: [PATCH v8 04/20] cachefiles: notify user daemon when withdrawing
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To:     David Howells <dhowells@redhat.com>
Cc:     linux-cachefs@redhat.com, xiang@kernel.org, chao@kernel.org,
        linux-erofs@lists.ozlabs.org, torvalds@linux-foundation.org,
        gregkh@linuxfoundation.org, willy@infradead.org,
        linux-fsdevel@vger.kernel.org, joseph.qi@linux.alibaba.com,
        bo.liu@linux.alibaba.com, tao.peng@linux.alibaba.com,
        gerry@linux.alibaba.com, eguan@linux.alibaba.com,
        linux-kernel@vger.kernel.org, luodaowen.backend@bytedance.com,
        tianzichen@kuaishou.com, fannaihao@baidu.com
References: <542f749c-b0f1-1de6-cb41-26e296afb2df@linux.alibaba.com>
 <20220406075612.60298-5-jefflexu@linux.alibaba.com>
 <20220406075612.60298-1-jefflexu@linux.alibaba.com>
 <1091405.1649680508@warthog.procyon.org.uk>
 <1094493.1649684554@warthog.procyon.org.uk>
From:   JeffleXu <jefflexu@linux.alibaba.com>
In-Reply-To: <1094493.1649684554@warthog.procyon.org.uk>
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On 4/11/22 9:42 PM, David Howells wrote:
> JeffleXu <jefflexu@linux.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