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From: Greg KH <>
To: Sven Van Asbroeck <>
Cc: Carlos <>,
Subject: Re: Exposing semaphores
Date: Tue, 27 Apr 2021 12:58:31 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Tue, Apr 27, 2021 at 06:18:52AM -0400, Sven Van Asbroeck wrote:
> Hi Carlos,
> On Mon, Apr 26, 2021 at 8:02 PM Carlos <> wrote:
> >
> > I recently began assessing what functionality from the kernel is missing
> > for implementing a basic scull driver.
> >
> > Semaphores are the first missing primitive that caught my attention, and
> > being such an important part of the kernel itself, I will make exposing
> > this functionality my first priority instead.
> Isn't scull's semaphore used exclusively in mutex mode, i.e.
> initialized using init_MUTEX?
> If so, prefer "struct mutex" instead. At the time scull was written
> (over 15 years ago) it did not yet exist.
> A Rust-for-Linux abstraction is already available:
> This is before my time, but I believe that the use of "bare" struct
> semaphores in drivers used to be a common anti-pattern, often
> resulting in buggy code and/or performance issues - most semaphores
> have been replaced by conceptually safer, higher-level primitives, and
> today one needs a valid excuse to use them in new or even refactored
> driver code. But I do not know the full story.

I agree, never try to ab-use a semaphore in the way we did it in the
book, that is not a good "pattern" to follow for the majority of kernel

A simple mutex should be all that is necessary.

But also, while the CUSE driver has a lot of history, it really was only
created as an example to show how things could work, it isn't all that
useful in the real world :)


greg k-h

      reply	other threads:[~2021-04-27 10:58 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-27  0:02 Exposing semaphores Carlos
2021-04-27  0:08 ` Alex Gaynor
2021-04-27  0:12 ` Wedson Almeida Filho
2021-04-27  1:43   ` Samantha Miller
2021-04-27 11:00   ` Sven Van Asbroeck
2021-04-27 10:18 ` Sven Van Asbroeck
2021-04-27 10:58   ` Greg KH [this message]

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