linux-kernel - Re: [PATCH 03/11] fs: add new read_uptr and write

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Date:   Wed, 24 Jun 2020 11:11:50 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 03/11] fs: add new read_uptr and write_uptr file operations

On Wed, Jun 24, 2020 at 10:55 AM Christoph Hellwig <hch@....de> wrote:
>
> I don't care at all.  Based on our previous chat I assumed you
> wanted something like this.  We might still need the uptr_t for
> setsockopt, though.

No.

What I mean was *not* something like uptr_t.

Just keep the existing "set_fs()". It's not harmful if it's only used
occasionally. We should rename it once it's rare enough, though.

Then, make the following changes:

 - all the normal user access functions stop caring. They use
TASK_SIZE_MAX and are done with it. They basically stop reacting to
set_fs().

 - then, we can have a few *very* specific cases (like setsockopt,
maybe some random read/write) that we teach to use the new set_fs()
thing.

So in *those* cases, we'd basically just do "oh, ok, we are supposed
to use a kernel pointer" based on the setfs value.

IOW, I mean tto do something much more gradual. No new interfaces, no
new types, just a couple of (very clearly marked!) cases of the legacy
set_fs() behavior.

                Linus