libsys: add standard condition spinning primitives

include/Makefile

@@ -22,7 +22,7 @@ INCS+=	minix/a.out.h minix/bitmap.h minix/callnr.h minix/cdrom.h \
 	minix/netdriver.h minix/partition.h minix/paths.h \
 	minix/portio.h minix/profile.h minix/queryparam.h \
 	minix/rs.h minix/safecopies.h minix/sched.h minix/sef.h minix/sound.h \
-	minix/sys_config.h minix/sysinfo.h minix/syslib.h \
+	minix/spin.h minix/sys_config.h minix/sysinfo.h minix/syslib.h \
 	minix/sysutil.h minix/timers.h minix/tty.h minix/type.h minix/types.h \
 	minix/u64.h minix/vfsif.h minix/vm.h \
 	minix/compiler.h minix/compiler-ack.h minix/sha2.h

include/minix/drivers.h

@@ -22,6 +22,7 @@
 #include <minix/syslib.h>
 #include <minix/sysutil.h>
 #include <minix/timers.h>
+#include <minix/spin.h>
 #include <minix/bitmap.h>
 
 #include <machine/interrupt.h>	/* IRQ vectors and miscellaneous ports */

include/minix/spin.h

@@ -0,0 +1,38 @@
+/* Prototypes for condition spinning helper functions (part of libsys). */
+#ifndef _MINIX_SPIN_H
+#define _MINIX_SPIN_H
+
+/* Opaque spin state structure. */
+typedef struct {
+	int s_state;
+	u32_t s_usecs;
+	u64_t s_base_tsc;
+	clock_t s_base_uptime;
+	int s_timeout;
+} spin_t;
+
+/* Functions. */
+_PROTOTYPE( void spin_init, (spin_t *s, u32_t usecs)			);
+_PROTOTYPE( int spin_check, (spin_t *s)					);
+
+/* Macros. */
+
+/* Execute a loop for at least 'u' microseconds, using spin object 's'.
+ * The body of the loop is guaranteed to be executed at least once.
+ */
+#define SPIN_FOR(s,u)							\
+	for (spin_init((s), (u)); spin_check((s)); )
+
+/* Return whether spin object 's' timed out after a loop. */
+#define SPIN_TIMEOUT(s) ((s)->s_timeout)
+
+/* Spin until the given condition becomes true, or 'u' microseconds expired.
+ * The condition is guaranteed to be checked at least once.
+ */
+#define SPIN_UNTIL(c,u) do {						\
+	spin_t s;							\
+	SPIN_FOR(&s,(u))						\
+		if (c) break;						\
+} while (0)
+
+#endif /* _MINIX_SPIN_H */