linux-kernel - Re: [PATCH v6 00/28] NT synchronization primitive driver

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Message-Id: <a6ec954d-7794-483d-a1f3-d58d33c5fc7a@app.fastmail.com>
Date: Mon, 09 Dec 2024 21:24:36 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Elizabeth Figura" <zfigura@...eweavers.com>,
 "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
 "Jonathan Corbet" <corbet@....net>, shuah <shuah@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
 wine-devel@...ehq.org,
 André Almeida <andrealmeid@...lia.com>,
 "Wolfram Sang" <wsa@...nel.org>, "Arkadiusz Hiler" <ahiler@...eweavers.com>,
 "Peter Zijlstra" <peterz@...radead.org>, "Andy Lutomirski" <luto@...nel.org>,
 linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org,
 "Randy Dunlap" <rdunlap@...radead.org>, "Ingo Molnar" <mingo@...hat.com>,
 "Will Deacon" <will@...nel.org>, "Waiman Long" <longman@...hat.com>,
 "Boqun Feng" <boqun.feng@...il.com>
Subject: Re: [PATCH v6 00/28] NT synchronization primitive driver

On Mon, Dec 9, 2024, at 19:58, Elizabeth Figura wrote:
> == Previous versions ==
>
> No changes were made from v5 other than rebasing on top of the 6.13-rc1
> char-misc-next tree.
>
> I would like to repeat a question from the last round of review, though. Two
> changes were suggested related to API design, which I did not make because the
> APIs in question were already released in upstream Linux. However, the driver is
> also completely nonfunctional and hidden behind BROKEN, so would this be
> acceptable anyway? The changes in question are:

If it was impossible to use the driver, there is no regression.
I feel the entire point of marking it as broken was to be able
to add that type of change.

> * rename NTSYNC_IOC_SEM_POST to NTSYNC_IOC_SEM_RELEASE (matching the NT
>   terminology instead of POSIX),

No objections my me on either name.

> * change object creation ioctls to return the fds directly in the return value
>   instead of through the args struct. I would also still appreciate a
>   clarification on the advice in [1], which is why I didn't do this in the first
>   place.
>
>   [1] https://docs.kernel.org/driver-api/ioctl.html#return-code

The git log tells me that I have written that, but I don't remember
why I put that in, maybe someone else suggested it.

My feeling right now is that returning a file descriptor number
as a small positive integer from the ioctl() return code makes
sense. On the other hand, returning pointers, negative signed
integers or large (> 32bit) 'unsigned long' values can cause
a number of issues, so I would avoid all those the same way we
discourage passing those integers as a literal 'arg' into ioctl()
instead of going through a pointer.

So either way, this looks good to me. I also looked through the
series again to double-check that you avoid the usual common
problems we list in Documentation/driver-api/ioctl.rst, and
I found this is all fine.

So with or without the two changes you listed:

Acked-by: Arnd Bergmann <arnd@...db.de>

      Arnd