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

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Date:   Mon, 11 Apr 2022 14:42:34 +0100
From:   David Howells <dhowells@...hat.com>
To:     JeffleXu <jefflexu@...ux.alibaba.com>
Cc:     dhowells@...hat.com, 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

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.

> 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.

David