feat: add PollFd, PrioQNode and PrioQueue

include/poll.h

@@ -0,0 +1,34 @@
+#ifndef FROSTBYTE_POLL_H
+#define FROSTBYTE_POLL_H
+
+#include "types.h"
+
+/*
+ * Real poll(2): waits for one or more file descriptors to become ready
+ * without picking, ahead of time, which single one to block on the way
+ * userRead/userWrite's own retry-the-syscall path already does for exactly
+ * one fd at a time (vfs.h's vfsBlockingChannel). Bit values match real
+ * Linux <poll.h> (POLLIN=0x1, POLLOUT=0x4, POLLERR=0x8, POLLHUP=0x10,
+ * POLLNVAL=0x20) even though nothing here reads a Linux binary's struct --
+ * there is no reason to invent different numbers for the same concept.
+ */
+#define pollIn   0x1
+#define pollOut  0x4
+#define pollErr  0x8
+#define pollHup  0x10
+#define pollNval 0x20
+
+typedef struct PollFd {
+    int32 fd;
+    int16 events;
+    int16 revents;
+} PollFd;
+
+/* Bounded the same way maxOpenFiles (vfs.h) bounds one process's own fd
+   table -- sysPoll (syscall.c) copies the caller's array into a fixed
+   kernel-stack buffer of exactly this size, so a request for more entries
+   than any one process could ever have open fds for is simply rejected
+   rather than silently truncated. */
+#define maxPollFds 16
+
+#endif