linux-kernel - Re: [PATCH 1/4] file: export __alloc

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Message-ID: <20180730214313.GF30522@ZenIV.linux.org.uk>
Date:   Mon, 30 Jul 2018 22:43:13 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Christian Brauner <christian@...uner.io>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        arve@...roid.com, tkjos@...roid.com, maco@...roid.com,
        rlove@...gle.com, ben@...adent.org.uk
Subject: Re: [PATCH 1/4] file: export __alloc_fd()

On Mon, Jul 30, 2018 at 01:36:33PM -0700, Matthew Wilcox wrote:
> On Mon, Jul 30, 2018 at 09:31:55AM -0700, Christoph Hellwig wrote:
> > On Mon, Jul 30, 2018 at 04:37:07PM +0200, Christian Brauner wrote:
> > > The Android binder driver will be turned into a module. Since it uses
> > > __alloc_fd() we need to export this function.
> > 
> > Err, hell no.
> > 
> > It should be using an anon fd probably.
> 
> I'm not entirely sure I understand the binder code (... does anyone?)
> but from what I can see, it intends to open a file descriptor in the
> process which is the target of the message being sent.  That strikes
> me as wrong-headed; it should be allocating a struct file and passing
> that file to the other process.  When that process receives the message,
> *it* allocates a file descriptor for itself.
> 
> But I think the binder user-space API relies on this.  The userspace API
> seems to rely on passing fd numbers around ... but I'm having trouble
> figuring most of this user API out.  Perhaps Martijn can help here.

... and there's a perfectly sane solution to that - it's called git rm.