[PATCH 3/4] meson: enforce a minimum Linux kernel headers version >= 4.18

["Daniel P. Berrangé" <berrange@redhat.com>]

Various areas of QEMU have a dependency on Linux kernel header
definitions. This falls under the scope of our supported platforms
matrix, but historically we've not checked for a minimum kernel
headers version. This has made it unclear when we can drop support
for older kernel headers.

  * Alpine 3.14: 5.10
  * CentOS 8: 4.18
  * CentOS 9: 5.14
  * Debian 10: 4.19
  * Debian 11: 5.10
  * Fedora 35: 5.19
  * Fedora 36: 5.19
  * OpenSUSE 15.3: 5.3.0
  * Ubuntu 20.04: 5.4
  * Ubuntu 22.04: 5.15

The above ignores the 3rd version digit since distros update their
packages periodically and such updates don't generally affect public
APIs to the extent that it matters for our build time check.

Overall, we can set the baseline to 4.18 currently.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 meson.build | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/meson.build b/meson.build
index 8dc661363f..ea434767ac 100644
--- a/meson.build
+++ b/meson.build
@@ -248,6 +248,18 @@ if targetos == 'linux'
   add_project_arguments('-isystem', meson.current_source_dir() / 'linux-headers',
                         '-isystem', 'linux-headers',
                         language: ['c', 'cpp'])
+
+  if not cc.compiles('''
+    #include <linux/version.h>
+    int main(void) {
+#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 18, 0)
+#error "QEMU requires Linux kernel headers version >= 4.18.0"
+#endif
+      return 0;
+    }''')
+  error('QEMU requires Linux kernel headers version >= 4.18.0')
+endif
+
 endif
 
 add_project_arguments('-iquote', '.',
-- 
2.37.3