Merge branch 'sg/t3701-tighten-trace'

diff --git a/compat/mingw.c b/compat/mingw.c
index 6ded1c859f1b5ae1ffe035ac228c0f8a5298097a..18caf21969a5917e8e6c6d754beffbba2741e6c2 100644 (file)
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -341,12 +341,74 @@ int mingw_mkdir(const char *path, int mode)
        return ret;
 }
 
+/*
+ * Calling CreateFile() using FILE_APPEND_DATA and without FILE_WRITE_DATA
+ * is documented in [1] as opening a writable file handle in append mode.
+ * (It is believed that) this is atomic since it is maintained by the
+ * kernel unlike the O_APPEND flag which is racily maintained by the CRT.
+ *
+ * [1] https://docs.microsoft.com/en-us/windows/desktop/fileio/file-access-rights-constants
+ *
+ * This trick does not appear to work for named pipes.  Instead it creates
+ * a named pipe client handle that cannot be written to.  Callers should
+ * just use the regular _wopen() for them.  (And since client handle gets
+ * bound to a unique server handle, it isn't really an issue.)
+ */
+static int mingw_open_append(wchar_t const *wfilename, int oflags, ...)
+{
+       HANDLE handle;
+       int fd;
+       DWORD create = (oflags & O_CREAT) ? OPEN_ALWAYS : OPEN_EXISTING;
+
+       /* only these flags are supported */
+       if ((oflags & ~O_CREAT) != (O_WRONLY | O_APPEND))
+               return errno = ENOSYS, -1;
+
+       /*
+        * FILE_SHARE_WRITE is required to permit child processes
+        * to append to the file.
+        */
+       handle = CreateFileW(wfilename, FILE_APPEND_DATA,
+                       FILE_SHARE_WRITE | FILE_SHARE_READ,
+                       NULL, create, FILE_ATTRIBUTE_NORMAL, NULL);
+       if (handle == INVALID_HANDLE_VALUE)
+               return errno = err_win_to_posix(GetLastError()), -1;
+
+       /*
+        * No O_APPEND here, because the CRT uses it only to reset the
+        * file pointer to EOF before each write(); but that is not
+        * necessary (and may lead to races) for a file created with
+        * FILE_APPEND_DATA.
+        */
+       fd = _open_osfhandle((intptr_t)handle, O_BINARY);
+       if (fd < 0)
+               CloseHandle(handle);
+       return fd;
+}
+
+/*
+ * Does the pathname map to the local named pipe filesystem?
+ * That is, does it have a "//./pipe/" prefix?
+ */
+static int is_local_named_pipe_path(const char *filename)
+{
+       return (is_dir_sep(filename[0]) &&
+               is_dir_sep(filename[1]) &&
+               filename[2] == '.'  &&
+               is_dir_sep(filename[3]) &&
+               !strncasecmp(filename+4, "pipe", 4) &&
+               is_dir_sep(filename[8]) &&
+               filename[9]);
+}
+
 int mingw_open (const char *filename, int oflags, ...)
 {
+       typedef int (*open_fn_t)(wchar_t const *wfilename, int oflags, ...);
        va_list args;
        unsigned mode;
        int fd;
        wchar_t wfilename[MAX_PATH];
+       open_fn_t open_fn;
 
        va_start(args, oflags);
        mode = va_arg(args, int);
@@ -355,9 +417,14 @@ int mingw_open (const char *filename, int oflags, ...)
        if (filename && !strcmp(filename, "/dev/null"))
                filename = "nul";
 
+       if ((oflags & O_APPEND) && !is_local_named_pipe_path(filename))
+               open_fn = mingw_open_append;
+       else
+               open_fn = _wopen;
+
        if (xutftowcs_path(wfilename, filename) < 0)
                return -1;
-       fd = _wopen(wfilename, oflags, mode);
+       fd = open_fn(wfilename, oflags, mode);
 
        if (fd < 0 && (oflags & O_ACCMODE) != O_RDONLY && errno == EACCES) {
                DWORD attrs = GetFileAttributesW(wfilename);
@@ -375,7 +442,7 @@ int mingw_open (const char *filename, int oflags, ...)
                 * CREATE_ALWAYS flag of CreateFile()).
                 */
                if (fd < 0 && errno == EACCES)
-                       fd = _wopen(wfilename, oflags & ~O_CREAT, mode);
+                       fd = open_fn(wfilename, oflags & ~O_CREAT, mode);
                if (fd >= 0 && set_hidden_flag(wfilename, 1))
                        warning("could not mark '%s' as hidden.", filename);
        }