linux-kernel - Re: [PATCH v2 0/7] syscore: Pass context data to callbacks

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Message-ID: <2025072218-decipher-spree-327d@gregkh>
Date: Tue, 22 Jul 2025 16:08:09 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Thierry Reding <thierry.reding@...il.com>
Cc: x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
	linux-riscv@...ts.infradead.org, linux-mips@...r.kernel.org,
	loongarch@...ts.linux.dev, linuxppc-dev@...ts.ozlabs.org,
	linux-sh@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/7] syscore: Pass context data to callbacks

On Tue, Jul 22, 2025 at 03:56:40PM +0200, Thierry Reding wrote:
> On Sat, Jul 19, 2025 at 08:52:41AM +0200, Greg Kroah-Hartman wrote:
> > On Fri, Jul 18, 2025 at 03:49:37PM +0200, Thierry Reding wrote:
> > > On Thu, Jul 17, 2025 at 02:11:41PM +0200, Greg Kroah-Hartman wrote:
> > > > On Thu, Jul 17, 2025 at 12:32:34PM +0200, Thierry Reding wrote:
> [...]
> > > 	struct syscore;
> > > 
> > > 	struct syscore_ops {
> > > 		int (*suspend)(struct syscore *syscore);
> > > 		void (*resume)(struct syscore *syscore);
> > > 		void (*shutdown)(struct syscore *syscore);
> > > 	};
> > > 
> > > 	struct syscore {
> > > 		const struct syscore_ops *ops;
> > > 		struct list_head node;
> > > 	};
> > > 
> > > Is that what you had in mind?
> > 
> > I missed the list_head, so yes, this would be better, but don't pass
> > back the syscore structure, how about just a void * instead, making the
> > whole container_of() stuff go away?
> 
> Yeah, that's a possibility. I personally don't like passing the void *
> around because it's easier to make mistakes that way. I also find it
> unintuitive because it doesn't immediately show you what the functions
> expect.
> 
> My understanding is that the container_of() should get optimized away
> most of the time, so there aren't any obvious downsides that I can see.

container_of() is just pointer math, but a cast is even faster :)

> But I don't feel very strongly, so if you have a strong preference for
> void pointers, I can do that.

That's what you really want to have here, it's a syscore data type
thing, that the callback wants to reference.  Just like a irqrequest_t
function passes back a void * that the handler "knows" how to deal with
properly.

thanks,

greg k-h