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

[AKASHI Takahiro]

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;
+		}
+
+		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)
 
 /*
-- 
2.14.1