[PATCH] export retained initrd in debugfs

[Milton Miller <miltonm@bga.com>]

Export initrd in debugfs when retained.

As a side effect, initrd_start and initrd_end are not cleared when the
initrd is retained.

After this patch, one can then copy the initrd space from debugfs and
pass it to kexec as the initrd, or do something else with it (maybe it
was an initrd not an initramfs).

Signed-off-by: Milton Miller <miltonm@bga.com>
--- 
This is a lot more reliable than extracting it via dd from /dev/mem.

Currently debugfs doesn't have a getattr even for blobs, so one has
to cp elsewhere before using kexec from kexec-tools.

Index: kernel/init/initramfs.c
===================================================================
--- kernel.orig/init/initramfs.c	2007-03-28 00:12:15.000000000 -0500
+++ kernel/init/initramfs.c	2007-03-28 00:35:56.000000000 -0500
@@ -6,6 +6,7 @@
 #include <linux/delay.h>
 #include <linux/string.h>
 #include <linux/syscalls.h>
+#include <linux/debugfs.h>
 
 static __initdata char *message;
 static void __init error(char *x)
@@ -519,7 +520,7 @@ static void __init free_initrd(void)
 	unsigned long crashk_end   = (unsigned long)__va(crashk_res.end);
 #endif
 	if (do_retain_initrd)
-		goto skip;
+		return;
 
 #ifdef CONFIG_KEXEC
 	/*
@@ -588,3 +589,29 @@ static int __init populate_rootfs(void)
 	return 0;
 }
 rootfs_initcall(populate_rootfs);
+
+#ifdef CONFIG_BLK_DEV_INITRD
+static struct debugfs_blob_wrapper initrd_blob;
+
+static int __init export_initrd(void)
+{
+	struct dentry *d;
+	initrd_blob.data = (char *)initrd_start;
+	initrd_blob.size = initrd_end - initrd_start;
+
+	if (!do_retain_initrd)
+		return 0;
+
+	if (!initrd_start)
+		return 0;
+
+	d = debugfs_create_blob("initrd", S_IFREG, NULL, &initrd_blob);
+
+	if (!d)
+		return 1;
+
+	return 0;
+}
+
+__initcall(export_initrd);
+#endif