[EFI] libdebian-installer: add efi subarch for amd64 and i386

[Steve McIntyre <steve@einval.com>]

Hi,

Looking through the Ubuntu version of debian-installer, I can see that
Colin and I independently came up with nigh-on exactly the same way to
deal with EFI systems, using a subarch to identify them. We've
differed very slightly in terms of the the source code in
libdebian-installer for checking for /sys/firmware/efi, but the effect
is the same. Here's my diff.

-- 
Steve McIntyre, Cambridge, UK.                                steve@einval.com
"I've only once written 'SQL is my bitch' in a comment. But that code 
 is in use on a military site..." -- Simon Booth

mr diff: /home/steve/debian/d-i/d-i/packages/libdebian-installer
diff --git a/debian/changelog b/debian/changelog
index ea88601..8e7866e 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -4,6 +4,9 @@ libdebian-installer (0.82) UNRELEASED; urgency=low
   * Support for reading hardware model from Device Tree (armel).
   * Add Dreamplug device (Kirkwood)
 
+  [ Steve McIntyre ]
+  * Add "efi" as a subarch for amd64
+
  -- Ian Campbell <ijc@hellion.org.uk>  Tue, 10 Jul 2012 21:15:56 +0000
 
 libdebian-installer (0.81) unstable; urgency=low
diff --git a/src/system/subarch-x86-linux.c b/src/system/subarch-x86-linux.c
index 567d3c2..e8bf343 100644
--- a/src/system/subarch-x86-linux.c
+++ b/src/system/subarch-x86-linux.c
@@ -250,6 +250,17 @@ static char *dmi_system_manufacturer(void)
        return ret;
 }
 
+/* Are we on an EFI system? Check to see if /sys/firmware/efi
+ * exists */
+static int is_efi(void)
+{
+       int ret = access("/sys/firmware/efi", R_OK);
+    if (ret == 0)
+               return 1;
+    else
+               return 0;
+}
+
 struct map {
        const char *entry;
        const char *ret;
@@ -267,6 +278,11 @@ const char *di_system_subarch_analyze(void)
        const char *ret = "generic";
        int i;
 
+       /* Look for generic EFI first; this will be over-ridden by the mac
+        * detection next if we're on a mac. */
+       if (is_efi())
+               ret = "efi";
+
        if (manufacturer)
        {
                for (i = 0; map_manufacturer[i].entry; i++)