Reintroduce f_type comparison macro

This reverts commit 4826f0b7b5c0aefa08b8cc7ef64d69027f84da2c.

Because statfs.t_type can be int on some architecures, we have to cast
the const magic to the type, otherwise the compiler warns about
signed/unsigned comparison, because the magic can be 32 bit unsigned.

statfs(2) man page is also wrong on some systems, because
f_type is not __SWORD_TYPE on some architecures.

The following program:

int main(int argc, char**argv)
{
        struct statfs s;
        statfs(argv[1], &s);

	printf("sizeof(f_type) = %d\n", sizeof(s.f_type));
	printf("sizeof(__SWORD_TYPE) = %d\n", sizeof(__SWORD_TYPE));
	printf("sizeof(long) = %d\n", sizeof(long));
	printf("sizeof(int) = %d\n", sizeof(int));
	if (sizeof(s.f_type) == sizeof(int)) {
		printf("f_type = 0x%x\n", s.f_type);
	} else {
                printf("f_type = 0x%lx\n", s.f_type);
	}
        return 0;
}

executed on s390x gives for a btrfs:

sizeof(f_type) = 4
sizeof(__SWORD_TYPE) = 8
sizeof(long) = 8
sizeof(int) = 4
f_type = 0x9123683e

1 files changed, 7 insertions, 0 deletions

diff --git a/src/shared/macro.h b/src/shared/macro.h
index 9bf81dc3cc..ac61b49588 100644
--- a/src/shared/macro.h
+++ b/src/shared/macro.h
@@ -264,6 +264,13 @@ do {                                                                    \
         }                                                               \
 } while(false)
 
+ /* Because statfs.t_type can be int on some architecures, we have to cast
+  * the const magic to the type, otherwise the compiler warns about
+  * signed/unsigned comparison, because the magic can be 32 bit unsigned.
+ */
+#define F_TYPE_CMP(a, b) (a == (typeof(a)) b)
+
+
 /* Returns the number of chars needed to format variables of the
  * specified type as a decimal string. Adds in extra space for a
  * negative '-' prefix. */