Add private mmap/munmap wrappers

Unlike Linux, Android (bionic) has separate functions - mmap & mmap64.
Add a local wrapper (inspired by gallium) that will be used throughout
libdrm to combat this bionic feature.

v2:
 - Drop the undefined unlikely macro.
 - Use macro for munmap under Android.
 - Wrap long lines.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Jakob Bornecrantz <jakob@vmware.com> (v1)

libdrm.h

@@ -31,4 +31,59 @@
 #  define drm_public
 #endif
 
+
+/**
+ * Static (compile-time) assertion.
+ * Basically, use COND to dimension an array.  If COND is false/zero the
+ * array size will be -1 and we'll get a compilation error.
+ */
+#define STATIC_ASSERT(COND) \
+   do { \
+      (void) sizeof(char [1 - 2*!(COND)]); \
+   } while (0)
+
+
+#include <sys/mman.h>
+
+#if defined(ANDROID)
+#include <errno.h> /* for EINVAL */
+
+extern void *__mmap2(void *, size_t, int, int, int, size_t);
+
+static inline void *drm_mmap(void *addr, size_t length, int prot, int flags,
+                             int fd, loff_t offset)
+{
+   /* offset must be aligned to 4096 (not necessarily the page size) */
+   if (offset & 4095) {
+      errno = EINVAL;
+      return MAP_FAILED;
+   }
+
+   return __mmap2(addr, length, prot, flags, fd, (size_t) (offset >> 12));
+}
+
+#  define drm_munmap(addr, length) \
+              munmap(addr, length)
+
+
+#else
+
+/* assume large file support exists */
+#  define drm_mmap(addr, length, prot, flags, fd, offset) \
+              mmap(addr, length, prot, flags, fd, offset)
+
+
+static inline int drm_munmap(void *addr, size_t length)
+{
+   /* Copied from configure code generated by AC_SYS_LARGEFILE */
+#define LARGE_OFF_T ((((off_t) 1 << 31) << 31) - 1 + \
+                     (((off_t) 1 << 31) << 31))
+   STATIC_ASSERT(LARGE_OFF_T % 2147483629 == 721 &&
+                 LARGE_OFF_T % 2147483647 == 1);
+#undef LARGE_OFF_T
+
+   return munmap(addr, length);
+}
+#endif
+
 #endif