Add raw memory visualization tool to redbean

This change introduces a `-W /dev/pts/1` flag to redbean. What it does
is use the mincore() system call to create a dual-screen terminal
display that lets you troubleshoot the virtual address space. This is
useful since page faults are an important thing to consider when using a
forking web server. Now we have a colorful visualization of which pages
are going to fault and which ones are resident in memory.

The memory monitor, if enabled, spawns as a thread that just outputs
ANSI codes to the second terminal in a loop. In order to make this
happen using the new clone() polyfill, stdio is now thread safe.

This change also introduces some new demo pages to redbean. It also
polishes the demos we already have, to look a bit nicer and more
presentable for the upcoming release, with better explanations too.

libc/calls/calls.h

@@ -21,14 +21,16 @@
 #define _POSIX2_VERSION _POSIX_VERSION
 #define _XOPEN_VERSION  700
 
-#define EOF      -1  /* end of file */
-#define WEOF     -1u /* end of file (multibyte) */
-#define _IOFBF   0   /* fully buffered */
-#define _IOLBF   1   /* line buffered */
-#define _IONBF   2   /* no buffering */
-#define SEEK_SET 0   /* relative to beginning */
-#define SEEK_CUR 1   /* relative to current position */
-#define SEEK_END 2   /* relative to end */
+#define EOF      -1         /* end of file */
+#define WEOF     -1u        /* end of file (multibyte) */
+#define _IOFBF   0          /* fully buffered */
+#define _IOLBF   1          /* line buffered */
+#define _IONBF   2          /* no buffering */
+#define SEEK_SET 0          /* relative to beginning */
+#define SEEK_CUR 1          /* relative to current position */
+#define SEEK_END 2          /* relative to end */
+#define __WALL   0x40000000 /* Wait on all children, regardless of type */
+#define __WCLONE 0x80000000 /* Wait only on non-SIGCHLD children */
 
 #define SIG_ERR ((void (*)(int))(-1))
 #define SIG_DFL ((void *)0)
@@ -147,6 +149,7 @@ int linkat(int, const char *, int, const char *, int);
 int lstat(const char *, struct stat *);
 int lutimes(const char *, const struct timeval[2]);
 int madvise(void *, uint64_t, int);
+int mincore(void *, size_t, unsigned char *);
 int mkdir(const char *, uint32_t);
 int mkdirat(int, const char *, uint32_t);
 int mkfifo(const char *, uint32_t);

libc/calls/fchown.c

@@ -18,6 +18,7 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/calls.h"
 #include "libc/calls/internal.h"
+#include "libc/calls/strace.internal.h"
 #include "libc/sysv/consts/at.h"
 
 /**
@@ -28,8 +29,11 @@
  * @return 0 on success, or -1 w/ errno
  * @see /etc/passwd for user ids
  * @see /etc/group for group ids
+ * @raises ENOSYS on Windows
  */
 int fchown(int fd, uint32_t uid, uint32_t gid) {
-  /* TODO(jart): Windows? */
-  return sys_fchown(fd, uid, gid);
+  int rc;
+  rc = sys_fchown(fd, uid, gid);
+  STRACE("fchown(%d, %d, %d) → %d% m", fd, uid, gid, rc);
+  return rc;
 }

libc/calls/internal.h

@@ -176,6 +176,7 @@ i32 sys_lseek(i32, i64, i64, i64) hidden;
 i32 sys_lutimes(const char *, const struct timeval *) hidden;
 i32 sys_madvise(void *, size_t, i32) hidden;
 i32 sys_memfd_create(const char *, u32) hidden;
+i32 sys_mincore(void *, u64, unsigned char *) hidden;
 i32 sys_mkdirat(i32, const char *, u32) hidden;
 i32 sys_mkfifo(const char *, u32) hidden;
 i32 sys_mknod(const char *, u32, u64) hidden;

libc/calls/mincore.c

@@ -0,0 +1,31 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2022 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/calls/calls.h"
+#include "libc/calls/internal.h"
+#include "libc/calls/strace.internal.h"
+
+/**
+ * Tells you which pages are resident in memory.
+ */
+int mincore(void *addr, size_t length, unsigned char *vec) {
+  int rc;
+  rc = sys_mincore(addr, length, vec);
+  POLLTRACE("mincore(%p, %'zu, %p) → %d% m", addr, length, vec, rc);
+  return rc;
+}

libc/calls/nanosleep.c

@@ -45,9 +45,9 @@ noinstrument int nanosleep(const struct timespec *req, struct timespec *rem) {
     rc = sys_nanosleep_nt(req, rem);
   }
   if (!__time_critical) {
-    STRACE("nanosleep(%s, [%s]) → %d% m",
-           DescribeTimespec(buf[0], sizeof(buf[0]), rc, req),
-           DescribeTimespec(buf[1], sizeof(buf[1]), rc, rem), rc);
+    POLLTRACE("nanosleep(%s, [%s]) → %d% m",
+              DescribeTimespec(buf[0], sizeof(buf[0]), rc, req),
+              DescribeTimespec(buf[1], sizeof(buf[1]), rc, rem), rc);
   }
   return rc;
 }