package/qemu: fix build of host-qemu on systems with old kernel headers

Qemu assumes that when <linux/usbdevice_fs.h> is available, it can
build its USBFS code. However, some systems have
<linux/usbdevice_fs.h>, but it doesn't provide all the definitions
that Qemu needs, causing a build failure.

In order to fix this, we introduce a Qemu patch that improves the
check that determines whether USBFS support should be enabled or not.

Fixes:

  http://autobuild.buildroot.net/results/c4af5505f80e1e6185df70d191e85d9393df5795/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/qemu/0002-configure-improve-usbfs-check.patch

@@ -0,0 +1,60 @@
+From 9672cccd64c446369b5649fe23d575917638be46 Mon Sep 17 00:00:00 2001
+From: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
+Date: Tue, 5 Feb 2019 15:07:43 +0100
+Subject: [PATCH] configure: improve usbfs check
+
+The current check to test if usbfs support should be compiled or not
+solely relies on the presence of <linux/usbdevice_fs.h>, without
+actually checking that all definition used by Qemu are provided by
+this header file.
+
+With sufficiently old kernel headers, <linux/usbdevice_fs.h> may be
+present, but some of the definitions needed by Qemu may not be
+available.
+
+This commit improves the check by building a small program that
+actually tests whether the necessary definitions are available.
+
+In addition, it fixes a bug where have_usbfs was set to "yes"
+regardless of the result of the test.
+
+Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
+---
+ configure | 19 +++++++++++++++++--
+ 1 file changed, 17 insertions(+), 2 deletions(-)
+
+diff --git a/configure b/configure
+index 3d89870d99..799c8e3b08 100755
+--- a/configure
++++ b/configure
+@@ -4266,10 +4266,25 @@ fi
+ # check for usbfs
+ have_usbfs=no
+ if test "$linux_user" = "yes"; then
+-  if check_include linux/usbdevice_fs.h; then
++  cat > $TMPC << EOF
++#include <linux/usbdevice_fs.h>
++
++#ifndef USBDEVFS_GET_CAPABILITIES
++#error "USBDEVFS_GET_CAPABILITIES undefined"
++#endif
++
++#ifndef USBDEVFS_DISCONNECT_CLAIM
++#error "USBDEVFS_DISCONNECT_CLAIM undefined"
++#endif
++
++int main(void)
++{
++    return 0;
++}
++EOF
++  if compile_prog "" ""; then
+     have_usbfs=yes
+   fi
+-  have_usbfs=yes
+ fi
+ 
+ # check for fallocate
+-- 
+2.20.1
+