Start documenting libc.

Bug: N/A
Test: N/A
Change-Id: I17345cb72a5ffc3af1688cf5874589cfb1e1fea0
diff --git a/libc/include/syslog.h b/libc/include/syslog.h
index fff565e..45de253 100644
--- a/libc/include/syslog.h
+++ b/libc/include/syslog.h
@@ -26,8 +26,7 @@
  * SUCH DAMAGE.
  */
 
-#ifndef _SYSLOG_H
-#define _SYSLOG_H
+#pragma once
 
 #include <stdio.h>
 #include <sys/cdefs.h>
@@ -35,63 +34,128 @@
 
 __BEGIN_DECLS
 
-/* Priorities are translated to Android log priorities as shown. */
-#define LOG_EMERG   0 /* ERROR */
-#define LOG_ALERT   1 /* ERROR */
-#define LOG_CRIT    2 /* ERROR */
-#define LOG_ERR     3 /* ERROR */
-#define LOG_WARNING 4 /* WARN */
-#define LOG_NOTICE  5 /* INFO */
-#define LOG_INFO    6 /* INFO */
-#define LOG_DEBUG   7 /* DEBUG */
+/** Corresponds to the Android ERROR log priority. */
+#define LOG_EMERG 0
+/** Corresponds to the Android ERROR log priority. */
+#define LOG_ALERT 1
+/** Corresponds to the Android ERROR log priority. */
+#define LOG_CRIT 2
+/** Corresponds to the Android ERROR log priority. */
+#define LOG_ERR 3
+/** Corresponds to the Android WARN log priority. */
+#define LOG_WARNING 4
+/** Corresponds to the Android INFO log priority. */
+#define LOG_NOTICE 5
+/** Corresponds to the Android INFO log priority. */
+#define LOG_INFO 6
+/** Corresponds to the Android DEBUG log priority. */
+#define LOG_DEBUG 7
 
 #define LOG_PRIMASK 7
 #define LOG_PRI(x) ((x) & LOG_PRIMASK)
 #define LOG_MAKEPRI(fac, pri) ((fac) | (pri))
 
-/* Facilities are currently ignored on Android. */
+/** Currently ignored on Android. */
 #define LOG_KERN     (0<<3)
+/** Currently ignored on Android. */
 #define LOG_USER     (1<<3)
+/** Currently ignored on Android. */
 #define LOG_MAIL     (2<<3)
+/** Currently ignored on Android. */
 #define LOG_DAEMON   (3<<3)
+/** Currently ignored on Android. */
 #define LOG_AUTH     (4<<3)
+/** Currently ignored on Android. */
 #define LOG_SYSLOG   (5<<3)
+/** Currently ignored on Android. */
 #define LOG_LPR      (6<<3)
+/** Currently ignored on Android. */
 #define LOG_NEWS     (7<<3)
+/** Currently ignored on Android. */
 #define LOG_UUCP     (8<<3)
+/** Currently ignored on Android. */
 #define LOG_CRON     (9<<3)
+/** Currently ignored on Android. */
 #define LOG_AUTHPRIV (10<<3)
+/** Currently ignored on Android. */
 #define LOG_FTP      (11<<3)
+/** Currently ignored on Android. */
 #define LOG_LOCAL0   (16<<3)
+/** Currently ignored on Android. */
 #define LOG_LOCAL1   (17<<3)
+/** Currently ignored on Android. */
 #define LOG_LOCAL2   (18<<3)
+/** Currently ignored on Android. */
 #define LOG_LOCAL3   (19<<3)
+/** Currently ignored on Android. */
 #define LOG_LOCAL4   (20<<3)
+/** Currently ignored on Android. */
 #define LOG_LOCAL5   (21<<3)
+/** Currently ignored on Android. */
 #define LOG_LOCAL6   (22<<3)
+/** Currently ignored on Android. */
 #define LOG_LOCAL7   (23<<3)
 
 #define LOG_NFACILITIES 24
 #define LOG_FACMASK 0x3f8
 #define LOG_FAC(x) (((x) >> 3) & (LOG_FACMASK >> 3))
 
+/**
+ * Converts a log priority into a mask enabling that single priority,
+ * for use with setlogmask().
+ */
 #define LOG_MASK(pri) (1 << (pri))
+
+/**
+ * Converts a log priority into a mask enabling that priority and all lower
+ * priorities, for use with setlogmask().
+ */
 #define LOG_UPTO(pri) ((1 << ((pri)+1)) - 1)
 
-/* openlog(3) flags are currently ignored on Android. */
+/** openlog() options are currently ignored on Android. */
 #define LOG_PID    0x01
+/** openlog() options are currently ignored on Android. */
 #define LOG_CONS   0x02
+/** openlog() options are currently ignored on Android. */
 #define LOG_ODELAY 0x04
+/** openlog() options are currently ignored on Android. */
 #define LOG_NDELAY 0x08
+/** openlog() options are currently ignored on Android. */
 #define LOG_NOWAIT 0x10
+/** openlog() options are currently ignored on Android. */
 #define LOG_PERROR 0x20
 
+/**
+ * [closelog(3)](http://man7.org/linux/man-pages/man3/closelog.3.html) does
+ * nothing on Android.
+ */
 void closelog(void);
+
+/**
+ * [openlog(3)](http://man7.org/linux/man-pages/man3/openlog.3.html) sets
+ * the log tag to `__prefix`. On Android, the other two arguments are ignored.
+ */
 void openlog(const char* __prefix, int __option, int __facility);
+
+/**
+ * [setlogmask(3)](http://man7.org/linux/man-pages/man3/setlogmask.3.html)
+ * sets which log priorities will actually be logged. See `LOG_MASK` and
+ * `LOG_UPTO`.
+ */
 int setlogmask(int __mask);
+
+/**
+ * [syslog(3)](http://man7.org/linux/man-pages/man3/syslog.3.html) formats
+ * the printf()-like message and logs it with the given priority, unless
+ * suppressed by setlogmask(). On Android, the output goes to logcat.
+ */
 void syslog(int __priority, const char* __fmt, ...) __printflike(2, 3);
+
+/**
+ * [vsyslog(3)](http://man7.org/linux/man-pages/man3/vsyslog.3.html) formats
+ * the vprintf()-like message and logs it with the given priority, unless
+ * suppressed by setlogmask(). On Android, the output goes to logcat.
+ */
 void vsyslog(int __priority, const char* __fmt, va_list __args) __printflike(2, 0);
 
 __END_DECLS
-
-#endif /* _SYSLOG_H */