Provide base::EvictFileFromSystemCache on Android on ARM32

base/test/test_file_util_linux.cc

Index: base/test/test_file_util_linux.cc
diff --git a/base/test/test_file_util_linux.cc b/base/test/test_file_util_linux.cc
index 0ef5c0a1571041da64665bbf1673f0cce268396d..6339aeef6b11559a01d6be4fde5da23ebbc26e14 100644
--- a/base/test/test_file_util_linux.cc
+++ b/base/test/test_file_util_linux.cc
@@ -9,11 +9,42 @@
 #include <sys/types.h>
 #include <unistd.h>
 
+#if defined(OS_ANDROID)
+#include <asm/unistd.h>
+#include <errno.h>
+#include <linux/fadvise.h>
+#include <sys/syscall.h>
+#endif
+
 #include "base/files/file_path.h"
 #include "base/files/scoped_file.h"
 
 namespace base {
 
+// Inconveniently, the NDK doesn't provide for posix_fadvise

[jbudorick, 2017/05/30 15:48:02]

Should this all just be in test_file_util_android.cc?

[Maks Orlovich, 2017/05/30 16:49:17]

I can bind "all" two different ways, and have different answers for them:

1) This new block (e.g. the posix_fadvise stub for Android):
   Putting it in a separate file would make it impossible for it to 
   be in an anonymous namespace, which feels like a bad idea. 
   (Less so if it's just in base:: than global, of course).

   Also we would still need the prototype to be declared somewhere,
   and to include linux/fadvise.h for the enums.

   I am strongly down on this idea because of it.

2) The entire file. The downside is code duplication, the upside is 
   less ifdefer'y and messing with filters in BUILD.gn. 

   I am slightly negative on the idea, but it's certainly feels 
   reasonable enough that consistent reviewer opinion will sway that.

[jbudorick, 2017/05/30 16:52:05]

This was what I meant. Your reasoning for keeping it here sounds fine.

+// until API level = 21, which we don't use yet, so provide a wrapper, at least

[jbudorick, 2017/05/30 15:48:02]

nit: note that this is *native* api level 21.

[Maks Orlovich, 2017/05/30 16:49:17]

Thanks for elaborating, I wasn't aware of this distinction.
Added

+// on ARM32
+#if defined(OS_ANDROID)

[jbudorick, 2017/05/30 15:48:02]

nit: Should this be

  if defined(OS_ANDROID) && __ANDROID_API__ < 21

?

[Maks Orlovich, 2017/05/30 16:49:17]

Done.

+
+namespace {
+int posix_fadvise(int fd, off_t offset, off_t len, int advice) {
+#if defined(ARCH_CPU_ARMEL)
+  // Note that the syscall argument order on ARM is different from the C
+  // function; this is helpfully documented in the Linux posix_fadvise manpage.
+  return syscall(__NR_arm_fadvise64_64, fd, advice,
+                 0,  // Upper 32-bits for offset
+                 offset,
+                 0,  // Upper 32-bits for length
+                 len);
+#endif
+  NOTIMPLEMENTED();
+  return ENOSYS;
+}
+
+}  // namespace
+
+#endif  // OS_ANDROID
+
 bool EvictFileFromSystemCache(const FilePath& file) {
   ScopedFD fd(open(file.value().c_str(), O_RDONLY));
   if (!fd.is_valid())