linux-kernel - Re: [PATCH] x86/cpuid: Use macro instead of number in cpuid

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Message-ID: <83699764-1956-4C58-8347-41A29A0687C4@zytor.com>
Date:   Thu, 05 Mar 2020 01:46:03 -0800
From:   hpa@...or.com
To:     Yu Chen <chen.yu@...ystack.cn>, tglx@...utronix.de
CC:     linux-kernel@...r.kernel.org, x86@...nel.org, yuchen1988@...yun.com
Subject: Re: [PATCH] x86/cpuid: Use macro instead of number in cpuid_read()

On March 5, 2020 1:33:18 AM PST, Yu Chen <chen.yu@...ystack.cn> wrote:
>Make and use macro CHUNK_SIZE, instead of numeric value 16 in
>cpuid_read().
>
>Signed-off-by: Yu Chen <chen.yu@...ystack.cn>
>---
> arch/x86/kernel/cpuid.c | 13 ++++++++-----
> 1 file changed, 8 insertions(+), 5 deletions(-)
>
>diff --git a/arch/x86/kernel/cpuid.c b/arch/x86/kernel/cpuid.c
>index 3492aa36b..f7d7e0ef7 100644
>--- a/arch/x86/kernel/cpuid.c
>+++ b/arch/x86/kernel/cpuid.c
>@@ -48,6 +48,9 @@ struct cpuid_regs_done {
> 	struct completion done;
> };
> 
>+/* cpuid must be read in chunks of 16 bytes */
>+#define CHUNK_SIZE	16
>+
> static void cpuid_smp_cpuid(void *cmd_block)
> {
> 	struct cpuid_regs_done *cmd = cmd_block;
>@@ -69,11 +72,11 @@ static ssize_t cpuid_read(struct file *file, char
>__user *buf,
> 	ssize_t bytes = 0;
> 	int err = 0;
> 
>-	if (count % 16)
>+	if (count % CHUNK_SIZE)
> 		return -EINVAL;	/* Invalid chunk size */
> 
> 	init_completion(&cmd.done);
>-	for (; count; count -= 16) {
>+	for (; count; count -= CHUNK_SIZE) {
> 		call_single_data_t csd = {
> 			.func = cpuid_smp_cpuid,
> 			.info = &cmd,
>@@ -86,12 +89,12 @@ static ssize_t cpuid_read(struct file *file, char
>__user *buf,
> 		if (err)
> 			break;
> 		wait_for_completion(&cmd.done);
>-		if (copy_to_user(tmp, &cmd.regs, 16)) {
>+		if (copy_to_user(tmp, &cmd.regs, CHUNK_SIZE)) {
> 			err = -EFAULT;
> 			break;
> 		}
>-		tmp += 16;
>-		bytes += 16;
>+		tmp += CHUNK_SIZE;
>+		bytes += CHUNK_SIZE;
> 		*ppos = ++pos;
> 		reinit_completion(&cmd.done);
> 	}

It would make more sense to define a structure and add it to a uapi header.
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.