linux-kernel - Re: [PATCH 3/5] fs: sys

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Date: Mon, 24 Jun 2024 00:13:36 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Kent Overstreet <kent.overstreet@...ux.dev>,
 linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: Jens Axboe <axboe@...nel.dk>, Kent Overstreet
 <kent.overstreet@...ux.dev>, brauner@...nel.org, viro@...iv.linux.org.uk,
 Bernd Schubert <bernd.schubert@...tmail.fm>, linux-mm@...ck.org, Josef
 Bacik <josef@...icpanda.com>
Subject: Re: [PATCH 3/5] fs: sys_ringbuffer

Kent!

On Sun, Jun 02 2024 at 20:33, Kent Overstreet wrote:
> +/*
> + * ringbuffer_ptrs - head and tail pointers for a ringbuffer, mappped to
> + * userspace:
> + */
> +struct ringbuffer_ptrs {

The naming is confusing. ringbuffer_ctrl or something like that would be
more clear because it's more than just the pointers, which are in fact
positions. You have size, mask ... too, no?

> +	/*
> +	 * We use u32s because this type is shared between the kernel and
> +	 * userspace - ulong/size_t won't work here, we might be 32bit userland
> +	 * and 64 bit kernel, and u64 would be preferable (reduced probability
> +	 * of ABA) but not all architectures can atomically read/write to a u64;
> +	 * we need to avoid torn reads/writes.

union rbmagic {
	u64	__val64;
        struct {
                // TOOTIRED: Add big/little endian voodoo
	        u32	__val32;
                u32	__unused;
        };
};

Plus a bunch of accessors which depend on BITS_PER_LONG, no?

Thanks,

        tglx