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Date:   Fri, 23 Jul 2021 08:08:06 -0700
From:   Keith Busch <kbusch@kernel.org>
To:     Wedson Almeida Filho <wedsonaf@google.com>
Cc:     Matthew Wilcox <willy@infradead.org>,
        Finn Behrens <finn@kloenk.dev>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
        Christoph Hellwig <hch@infradead.org>,
        Miguel Ojeda <ojeda@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        rust-for-linux <rust-for-linux@vger.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Linux Doc Mailing List <linux-doc@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 00/17] Rust support
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On Thu, Jul 22, 2021 at 11:55:58PM +0100, Wedson Almeida Filho wrote:
> On Thu, Jul 08, 2021 at 01:58:32AM +0100, Matthew Wilcox wrote:
> > A simple NVMe driver is less than a thousand lines of C.
> > I know the one in the kernel now is ridiculously complicated and has
> > been thoroughly messed up with abstractions to support NVMeoF instead
> > of having a separate driver, but it's really a simple interface at heart.
> 
> The latest NVMe spec is 452 pages long, which seems to contradict your claim
> that it's simple. In any case, translating less than 1K lines of C shouldn't be
> too hard (after I've built the abstractions, of course). Would you mind sharing
> the simple driver you mention above?

You can use the 1.0 spec, which is much shorter. A 1.0 capable driver
should be forward compatible with newer devices, too.

The current nvme driver became less simple since blk-mq integration and
has only gotten more complicated since then with other transports and
more advanced features. For a simpler example, you can reference an in
kernel version <= 3.16, and ignore the "nvme-scsi" parts.