linux-kernel - Re: [PATCH 1/2] resource: add walk_system_ram_res

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Message-ID: <ZVQTkqSa4FA6b6iH@MiWiFi-R3L-srv>
Date:   Wed, 15 Nov 2023 08:40:50 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
        x86@...nel.org, linux-parisc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org, ebiederm@...ssion.com,
        takahiro.akashi@...aro.org
Subject: Re: [PATCH 1/2] resource: add walk_system_ram_res_rev()

On 11/14/23 at 03:17pm, Andrew Morton wrote:
> On Tue, 14 Nov 2023 17:16:57 +0800 Baoquan He <bhe@...hat.com> wrote:
> 
> > This function, being a variant of walk_system_ram_res() introduced in
> > commit 8c86e70acead ("resource: provide new functions to walk through
> > resources"), walks through a list of all the resources of System RAM
> > in reversed order, i.e., from higher to lower.
> > 
> > It will be used in kexec_file code to load kernel, initrd etc when
> > preparing kexec reboot.
> >
> > ...
> >
> > +/*
> > + * This function, being a variant of walk_system_ram_res(), calls the @func
> > + * callback against all memory ranges of type System RAM which are marked as
> > + * IORESOURCE_SYSTEM_RAM and IORESOUCE_BUSY in reversed order, i.e., from
> > + * higher to lower.
> > + */
> > +int walk_system_ram_res_rev(u64 start, u64 end, void *arg,
> > +				int (*func)(struct resource *, void *))
> > +{
> > +	struct resource res, *rams;
> > +	int rams_size = 16, i;
> > +	unsigned long flags;
> > +	int ret = -1;
> > +
> > +	/* create a list */
> > +	rams = kvcalloc(rams_size, sizeof(struct resource), GFP_KERNEL);
> > +	if (!rams)
> > +		return ret;
> > +
> > +	flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
> > +	i = 0;
> > +	while ((start < end) &&
> > +		(!find_next_iomem_res(start, end, flags, IORES_DESC_NONE, &res))) {
> > +		if (i >= rams_size) {
> > +			/* re-alloc */
> > +			struct resource *rams_new;
> > +			int rams_new_size;
> > +
> > +			rams_new_size = rams_size + 16;
> > +			rams_new = kvcalloc(rams_new_size, sizeof(struct resource),
> > +					    GFP_KERNEL);
> 
> kvrealloc()?

Exactly. Will udpate. Thanks for the great suggestion.

> 
> > +			if (!rams_new)
> > +				goto out;
> > +
> > +			memcpy(rams_new, rams,
> > +					sizeof(struct resource) * rams_size);
> > +			kvfree(rams);
> > +			rams = rams_new;
> > +			rams_size = rams_new_size;
> > +		}
> > +
> > +		rams[i].start = res.start;
> > +		rams[i++].end = res.end;
> > +
> > +		start = res.end + 1;
> > +	}
> > +
> > +	/* go reverse */
> > +	for (i--; i >= 0; i--) {
> > +		ret = (*func)(&rams[i], arg);
> > +		if (ret)
> > +			break;
> > +	}
> > +
> > +out:
> > +	kvfree(rams);
> > +	return ret;
> > +}
> > +
> >  /*
> >   * This function calls the @func callback against all memory ranges, which
> >   * are ranges marked as IORESOURCE_MEM and IORESOUCE_BUSY.
> > -- 
> > 2.41.0
>