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.aka...@linaro.org>
Cc: Vivek Goyal <vgo...@redhat.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Linus Torvalds <torva...@linux-foundation.org>
---
  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