Re: [PATCH 03/14] resource: add walk_system_ram_res_rev()

[Pratyush Anand]

On Thursday 24 August 2017 01:48 PM, AKASHI Takahiro 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 implementation on arm64.
>
> Signed-off-by: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx>
> Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> ---
>   include/linux/ioport.h |  3 +++
>   kernel/resource.c      | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 51 insertions(+)
>
> diff --git a/include/linux/ioport.h b/include/linux/ioport.h
> index 6230064d7f95..9a212266299f 100644
> --- a/include/linux/ioport.h
> +++ b/include/linux/ioport.h
> @@ -271,6 +271,9 @@ extern int
>   walk_system_ram_res(u64 start, u64 end, void *arg,
>   		    int (*func)(u64, u64, void *));
>   extern int
> +walk_system_ram_res_rev(u64 start, u64 end, void *arg,
> +			int (*func)(u64, u64, void *));
> +extern int
>   walk_iomem_res_desc(unsigned long desc, unsigned long flags, u64 start, u64 end,
>   		    void *arg, int (*func)(u64, u64, void *));
>   
> diff --git a/kernel/resource.c b/kernel/resource.c
> index 9b5f04404152..1d6d734c75ac 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -23,6 +23,7 @@
>   #include <linux/pfn.h>
>   #include <linux/mm.h>
>   #include <linux/resource_ext.h>
> +#include <linux/vmalloc.h>
>   #include <asm/io.h>
>   
>   
> @@ -469,6 +470,53 @@ int walk_system_ram_res(u64 start, u64 end, void *arg,
>   	return ret;
>   }
>   
> +int walk_system_ram_res_rev(u64 start, u64 end, void *arg,
> +				int (*func)(u64, u64, void *))
> +{
> +	struct resource res, *rams;
> +	u64 orig_end;
> +	int count, i;
> +	int ret = -1;
> +
> +	count = 16; /* initial */
> +again:
> +	/* create a list */
> +	rams = vmalloc(sizeof(struct resource) * count);
> +	if (!rams)
> +		return ret;
> +
> +	res.start = start;
> +	res.end = end;
> +	res.flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
> +	orig_end = res.end;
> +	i = 0;
> +	while ((res.start < res.end) &&
> +		(!find_next_iomem_res(&res, IORES_DESC_NONE, true))) {
> +		if (i >= count) {
> +			/* unlikely but */
> +			vfree(rams);
> +			count += 16;
> +			goto again;

Wounld't it be better to re-alloc a bigger space,copy previous values and free 
the previous pointer, instead of going *again*.

> +		}
> +
> +		rams[i].start = res.start;
> +		rams[i++].end = res.end;
> +
> +		res.start = res.end + 1;
> +		res.end = orig_end;
> +	}
> +
> +	/* go reverse */
> +	for (i--; i >= 0; i--) {
> +		ret = (*func)(rams[i].start, rams[i].end, arg);
> +		if (ret)
> +			break;
> +	}
> +
> +	vfree(rams);
> +	return ret;
> +}
> +
>   #if !defined(CONFIG_ARCH_HAS_WALK_MEMORY)
>   
>   /*

--
Regards
Pratyush