linux-kernel - Re: [PATCH v2 3/8] crash_core: change parse_crashkernel() to support crashkernel=,high|low parsing

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Date:   Tue, 5 Sep 2023 16:29:25 +0800
From:   Baoquan He <bhe@...hat.com>
To:     "Leizhen (ThunderTown)" <thunder.leizhen@...weicloud.com>
Cc:     linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        catalin.marinas@....com, thunder.leizhen@...wei.com,
        dyoung@...hat.com, prudo@...hat.com, samuel.holland@...ive.com,
        kexec@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
        x86@...nel.org
Subject: Re: [PATCH v2 3/8] crash_core: change parse_crashkernel() to support
 crashkernel=,high|low parsing

On 09/04/23 at 10:47am, Leizhen (ThunderTown) wrote:
> 
> 
> On 2023/9/1 17:49, Baoquan He wrote:
> >>> +
> >>> +		*high = true;
> >>> +	} else if (ret || !*crash_size) {
> >> This check can be moved outside of #ifdef. Because even '!high', it's completely
> >> applicable. The overall adjustment is as follows:
> > Hmm, the current logic is much easier to understand. However, I may not
> > 100% get your suggestion. Can you paste the complete code in your
> > suggested way? Do not need 100% correct code, just the skeleton of code logic
> > so that I can better understand it and add inline comment.
> 
> int __init parse_crashkernel(...)
> {
> 	int ret;
> 
> 	/* crashkernel=X[@offset] */
> 	ret = __parse_crashkernel(cmdline, system_ram, crash_size,
> 				crash_base, NULL);
> 
> #ifdef CONFIG_ARCH_HAS_GENERIC_CRASHKERNEL_RESERVATION
> 	if (high && ret == -ENOENT) {
> 		... ...		//The code for your original branch "else if (ret == -ENOENT) {"
> 		ret = 0;	//Added based on the next discussion
> 	}
> +#endif
> 
>  	if (!*crash_size)
> 		ret = -EINVAL;
> 
> 	return ret;
> }
> 
Thanks, Zhen Lei.

I paste the whole parse_crashkernel() as you suggested at bottom. Please
check if it's what you want. To me, both is fine to me. I have two minor
concerns to your suggested way.

1)
I took the "if (!high) return" way because except of x86/arm64, all
other architectures will call parse_crashkerne() and check
if *crash_size ==0. Please try 'git grep "parse_crashkernel(" arch'
and check those call sites. With that, we will have duplicated checking.

        ret = __parse_crashkernel(cmdline, system_ram, crash_size,
                                crash_base, NULL);
        if (!high)
                return ret;
2)
I actually like below branch and the code comment. It can give people
hint about what's going on in that case. Discarding it is a little pity.

        } else if (ret || !*crash_size) {
                /* The specified value is invalid */
                return -1;
        }

int __init parse_crashkernel(...)
{
	int ret;

	/* crashkernel=X[@offset] */
	ret = __parse_crashkernel(cmdline, system_ram, crash_size,
				crash_base, NULL);
#ifdef CONFIG_ARCH_HAS_GENERIC_CRASHKERNEL_RESERVATION
	if (high && ret == -ENOENT) {
		ret = __parse_crashkernel(cmdline, 0, crash_size,
				crash_base, suffix_tbl[SUFFIX_HIGH]);
		if (ret || !*crash_size)
			return -EINVAL;

		/*
		 * crashkernel=Y,low can be specified or not, but invalid value
		 * is not allowed.
		 */
		ret = __parse_crashkernel(cmdline, 0, low_size,
				crash_base, suffix_tbl[SUFFIX_LOW]);
		if (ret == -ENOENT) {
			*low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
			ret = 0;
		} else if (ret) {
			return ret;
		}

		*high = true;
	}
#endif

	if (!*crash_size)
		ret = -EINVAL;

	return ret;
}