netdev - Re: [PATCH v3 bpf-next 01/10] treewide: remove struct-pass-by-value from tracepoints arguments

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Message-ID: <20180322141119.7c876c13@gandalf.local.home>
Date:   Thu, 22 Mar 2018 14:11:19 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Alexei Starovoitov <ast@...com>
Cc:     <davem@...emloft.net>, <daniel@...earbox.net>,
        <torvalds@...ux-foundation.org>, <peterz@...radead.org>,
        <netdev@...r.kernel.org>, <kernel-team@...com>,
        <linux-api@...r.kernel.org>
Subject: Re: [PATCH v3 bpf-next 01/10] treewide: remove struct-pass-by-value
 from tracepoints arguments

On Thu, 22 Mar 2018 11:01:48 -0700
Alexei Starovoitov <ast@...com> wrote:

> From: Alexei Starovoitov <ast@...nel.org>
> 
> Fix all tracepoint arguments to pass structures (large and small) by reference
> instead of by value.
> Avoiding passing large structs by value is a good coding style.
> Passing small structs sometimes is beneficial, but in all cases
> it makes no difference vs readability of the code.
> The subsequent patch enforces that all tracepoints args are either integers
> or pointers and fit into 64-bit.

But some of these structures are used to force type checking, and are
just the same size as a number. That's why they don't have "struct" in
front of them. Like pmd_t. Will the subsequent patches really break if
the structure itself has one element that is of size long? Just seems
to add extra code to pass in an address to something that fits into a
single register.

-- Steve