statfs: change Linux feature detection

statfs: change Linux feature detection

Previously we check three things: "statfs" function, "linux/magic.h" and
"sys/vfs.h" headers. But we didn't check "struct statfs" or the "f_type"
field. That means if a system has "statfs" but "struct statfs" is not
defined in the two header files we check, or defined without the "f_type"
field, the compilation will fail.

This patch combines the checks (2 headers + 1 function + 1 field) together
and sets "HAVE_LINUX_STATFS". It makes setup.py faster (less checks), and
more reliable (immutable to the issue above).

--- a/mercurial/osutil.c	Fri Mar 24 16:20:10 2017 -0700
+++ b/mercurial/osutil.c	Fri Mar 24 14:59:19 2017 -0700
@@ -24,16 +24,14 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
-#ifdef HAVE_LINUX_MAGIC_H
+#ifdef HAVE_LINUX_STATFS
 #include <linux/magic.h>
+#include <sys/vfs.h>
 #endif
 #ifdef HAVE_BSD_STATFS
 #include <sys/mount.h>
 #include <sys/param.h>
 #endif
-#ifdef HAVE_SYS_VFS_H
-#include <sys/vfs.h>
-#endif
 #endif
 
 #ifdef __APPLE__
@@ -796,7 +794,7 @@
 }
 #endif /* ndef SETPROCNAME_USE_NONE */
 
-#ifdef HAVE_STATFS
+#if defined(HAVE_BSD_STATFS) || defined(HAVE_LINUX_STATFS)
 /* given a directory path, return filesystem type (best-effort), or None */
 const char *getfstype(const char *path) {
 #ifdef HAVE_BSD_STATFS
@@ -810,10 +808,10 @@
 	r = statfs(path, &buf);
 	if (r != 0)
 		return NULL;
-#ifdef HAVE_BSD_STATFS
+#if defined(HAVE_BSD_STATFS)
 	/* BSD or OSX provides a f_fstypename field */
 	return buf.f_fstypename;
-#endif
+#elif defined(HAVE_LINUX_STATFS)
 	/* Begin of Linux filesystems */
 #ifdef ADFS_SUPER_MAGIC
 	if (buf.f_type == ADFS_SUPER_MAGIC)
@@ -1084,6 +1082,7 @@
 		return "xfs";
 #endif
 	/* End of Linux filesystems */
+#endif /* def HAVE_LINUX_STATFS */
 	return NULL;
 }
 
@@ -1100,7 +1099,7 @@
 	PyObject *result = Py_BuildValue("s", type);
 	return result;
 }
-#endif /* def HAVE_STATFS */
+#endif /* defined(HAVE_LINUX_STATFS) || defined(HAVE_BSD_STATFS) */
 
 #endif /* ndef _WIN32 */
 
@@ -1278,7 +1277,7 @@
 	{"setprocname", (PyCFunction)setprocname, METH_VARARGS,
 	 "set process title (best-effort)\n"},
 #endif
-#ifdef HAVE_STATFS
+#if defined(HAVE_BSD_STATFS) || defined(HAVE_LINUX_STATFS)
 	{"getfstype", (PyCFunction)pygetfstype, METH_VARARGS,
 	 "get filesystem type (best-effort)\n"},
 #endif

--- a/setup.py	Fri Mar 24 16:20:10 2017 -0700
+++ b/setup.py	Fri Mar 24 14:59:19 2017 -0700
@@ -591,24 +591,21 @@
 osutil_ldflags = []
 
 # platform specific macros
-for plat, func in [('bsd', 'setproctitle'), ('bsd|darwin|linux', 'statfs')]:
+for plat, func in [('bsd', 'setproctitle')]:
     if re.search(plat, sys.platform) and hasfunction(new_compiler(), func):
         osutil_cflags.append('-DHAVE_%s' % func.upper())
 
-for plat, header in [
-    ('linux', 'linux/magic.h'),
-    ('linux', 'sys/vfs.h'),
-]:
-    if re.search(plat, sys.platform) and hasheader(new_compiler(), header):
-        macro = header.replace('/', '_').replace('.', '_').upper()
-        osutil_cflags.append('-DHAVE_%s' % macro)
-
 for plat, macro, code in [
     ('bsd|darwin', 'BSD_STATFS', '''
      #include <sys/param.h>
      #include <sys/mount.h>
      int main() { struct statfs s; return sizeof(s.f_fstypename); }
      '''),
+    ('linux', 'LINUX_STATFS', '''
+     #include <linux/magic.h>
+     #include <sys/vfs.h>
+     int main() { struct statfs s; return sizeof(s.f_type); }
+     '''),
 ]:
     if re.search(plat, sys.platform) and cancompile(new_compiler(), code):
         osutil_cflags.append('-DHAVE_%s' % macro)