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

From: Pratyush Anand
Date: Wed Aug 30 2017 - 22:35:05 EST




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