Make improvements

- Introduce ualarm() function
- Make rename() report EISEMPTY on Windows
- Always raise EINVAL upon open(O_RDONLY|O_TRUNC)
- Add macro so ./configure will detect SOCK_CLOEXEC
- Fix O_TRUNC without O_CREAT not working on Windows
- Let fcntl(F_SETFL) change O_APPEND status on Windows
- Make sure pwrite() / pread() report ESPIPE on sockets
- Raise ESPIPE on Windows when pwrite() is used on pipe
- Properly compute O_APPEND CreateFile() flags on Windows
- Don't require O_DIRECTORY to open directories on Windows
- Fix more instances of Windows reporting EISDIR and ENOTDIR
- Normalize EFTYPE and EMLINK to ELOOP on NetBSD and FreeBSD
- Make unlink() / rmdir() work on read-only files on Windows
- Validate UTF-8 on Windows paths to fix bug with overlong NUL
- Always print signal name to stderr when crashing due to SIG_DFL
- Fix Windows bug where denormalized paths >260 chars didn't work
- Block signals on BSDs when thread exits before trashing its own stack

libc/calls/fcntl-nt.c

@@ -26,10 +26,13 @@
 #include "libc/calls/wincrash.internal.h"
 #include "libc/errno.h"
 #include "libc/intrin/kmalloc.h"
+#include "libc/intrin/kprintf.h"
 #include "libc/intrin/weaken.h"
 #include "libc/limits.h"
 #include "libc/log/backtrace.internal.h"
 #include "libc/macros.internal.h"
+#include "libc/nt/createfile.h"
+#include "libc/nt/enum/fileflagandattributes.h"
 #include "libc/nt/enum/filelockflags.h"
 #include "libc/nt/errors.h"
 #include "libc/nt/files.h"
@@ -310,52 +313,63 @@ static textwindows int sys_fcntl_nt_dupfd(int fd, int cmd, int start) {
   return sys_dup_nt(fd, -1, (cmd == F_DUPFD_CLOEXEC ? O_CLOEXEC : 0), start);
 }
 
-static textwindows int sys_fcntl_nt_setfl(int fd, unsigned *flags, unsigned arg,
-                                          unsigned supported) {
-  unsigned old, neu, changed, other, allowed;
-  old = *flags & supported;
-  other = *flags & ~supported;
-  neu = arg & supported;
-  changed = old ^ neu;
-  // you may change the following access mode flags:
+static textwindows int sys_fcntl_nt_setfl(int fd, unsigned *flags,
+                                          unsigned mode, unsigned arg,
+                                          intptr_t *handle) {
+
+  // you may change the following:
   //
   // - O_NONBLOCK     make read() raise EAGAIN
-  // - O_NDELAY       same thing as O_NONBLOCK
-  // - O_ACCMODE      but has a minimal effect
+  // - O_APPEND       for toggling append mode
+  // - O_RANDOM       alt. for posix_fadvise()
+  // - O_SEQUENTIAL   alt. for posix_fadvise()
+  // - O_DIRECT       works but haven't tested
   //
-  allowed = O_ACCMODE | O_NONBLOCK;
-  if (changed & ~allowed) {
-    // the following access mode flags are supported, but it's currently
-    // not possible to change them on windows.
-    //
-    // - O_APPEND     tried to support but failed
-    // - O_RANDOM     use posix_fadvise() instead
-    // - O_SEQUENTIAL use posix_fadvise() instead
-    // - O_DIRECT     possibly in future?
-    // - O_DSYNC      possibly in future?
-    // - O_RSYNC      possibly in future?
-    // - O_SYNC       possibly in future?
-    //
-    return enotsup();
+  // the other bits are ignored.
+  unsigned allowed = O_APPEND | O_SEQUENTIAL | O_RANDOM | O_DIRECT | O_NONBLOCK;
+  unsigned needreo = O_APPEND | O_SEQUENTIAL | O_RANDOM | O_DIRECT;
+  unsigned newflag = (*flags & ~allowed) | (arg & allowed);
+
+  if ((*flags & needreo) ^ (arg & needreo)) {
+    unsigned perm, share, attr;
+    if (GetNtOpenFlags(newflag, mode, &perm, &share, 0, &attr) == -1) {
+      return -1;
+    }
+    // MSDN says only these are allowed, otherwise it returns EINVAL.
+    attr &= kNtFileFlagBackupSemantics | kNtFileFlagDeleteOnClose |
+            kNtFileFlagNoBuffering | kNtFileFlagOpenNoRecall |
+            kNtFileFlagOpenReparsePoint | kNtFileFlagOverlapped |
+            kNtFileFlagPosixSemantics | kNtFileFlagRandomAccess |
+            kNtFileFlagSequentialScan | kNtFileFlagWriteThrough;
+    intptr_t hand;
+    if ((hand = ReOpenFile(*handle, perm, share, attr)) != -1) {
+      if (hand != *handle) {
+        CloseHandle(*handle);
+        *handle = hand;
+      }
+    } else {
+      return __winerr();
+    }
   }
+
   // 1. ignore flags that aren't access mode flags
   // 2. return zero if nothing's changed
-  *flags = other | neu;
+  *flags = newflag;
   return 0;
 }
 
 textwindows int sys_fcntl_nt(int fd, int cmd, uintptr_t arg) {
   int rc;
   uint32_t flags;
-  int access_mode_flags = O_ACCMODE | O_APPEND | O_ASYNC | O_DIRECT |
-                          O_NOATIME | O_NONBLOCK | O_RANDOM | O_SEQUENTIAL;
   if (__isfdkind(fd, kFdFile) ||    //
       __isfdkind(fd, kFdSocket) ||  //
       __isfdkind(fd, kFdConsole)) {
     if (cmd == F_GETFL) {
-      rc = g_fds.p[fd].flags & access_mode_flags;
+      rc = g_fds.p[fd].flags & (O_ACCMODE | O_APPEND | O_DIRECT | O_NONBLOCK |
+                                O_RANDOM | O_SEQUENTIAL);
     } else if (cmd == F_SETFL) {
-      rc = sys_fcntl_nt_setfl(fd, &g_fds.p[fd].flags, arg, access_mode_flags);
+      rc = sys_fcntl_nt_setfl(fd, &g_fds.p[fd].flags, g_fds.p[fd].mode, arg,
+                              &g_fds.p[fd].handle);
     } else if (cmd == F_GETFD) {
       if (g_fds.p[fd].flags & O_CLOEXEC) {
         rc = FD_CLOEXEC;