[PATCH v2 1/2] resource: add walk_system_ram_res_rev()

[Baoquan He]

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.

Signed-off-by: AKASHI Takahiro <takahiro.aka...@linaro.org>
Signed-off-by: Baoquan He <b...@redhat.com>
---
v1->v2:
- Use kvrealloc() to reallocate memory instead of kvcalloc(), this
  simplifies code. Suggested by Andrew.

 include/linux/ioport.h |  3 +++
 kernel/resource.c      | 57 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 60 insertions(+)

diff --git a/include/linux/ioport.h b/include/linux/ioport.h
index 14f5cfabbbc8..db7fe25f3370 100644
--- a/include/linux/ioport.h
+++ b/include/linux/ioport.h
@@ -331,6 +331,9 @@ extern int
 walk_system_ram_res(u64 start, u64 end, void *arg,
                    int (*func)(struct resource *, void *));
 extern int
+walk_system_ram_res_rev(u64 start, u64 end, void *arg,
+                       int (*func)(struct resource *, void *));
+extern int
 walk_iomem_res_desc(unsigned long desc, unsigned long flags, u64 start, u64 
end,
                    void *arg, int (*func)(struct resource *, void *));
 
diff --git a/kernel/resource.c b/kernel/resource.c
index 866ef3663a0b..e8a244300e5b 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -27,6 +27,8 @@
 #include <linux/mount.h>
 #include <linux/resource_ext.h>
 #include <uapi/linux/magic.h>
+#include <linux/string.h>
+#include <linux/vmalloc.h>
 #include <asm/io.h>
 
 
@@ -429,6 +431,61 @@ int walk_system_ram_res(u64 start, u64 end, void *arg,
                                     func);
 }
 
+/*
+ * 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;
+
+                       rams_new = kvrealloc(rams, rams_size * sizeof(struct 
resource),
+                                            (rams_size + 16) * sizeof(struct 
resource),
+                                            GFP_KERNEL);
+                       if (!rams_new)
+                               goto out;
+
+                       rams = rams_new;
+                       rams_size += 16;
+               }
+
+               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