diff options
Diffstat (limited to 'compat/mingw.c')
| -rw-r--r-- | compat/mingw.c | 36 |
1 files changed, 33 insertions, 3 deletions
diff --git a/compat/mingw.c b/compat/mingw.c index 858ca14a57..18caf21969 100644 --- a/compat/mingw.c +++ b/compat/mingw.c @@ -341,6 +341,19 @@ 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; @@ -360,10 +373,12 @@ static int mingw_open_append(wchar_t const *wfilename, int oflags, ...) 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 on write(); but that is not necessary - * for a file created with FILE_APPEND_DATA. + * 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) @@ -371,6 +386,21 @@ static int mingw_open_append(wchar_t const *wfilename, int oflags, ...) 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, ...); @@ -387,7 +417,7 @@ int mingw_open (const char *filename, int oflags, ...) if (filename && !strcmp(filename, "/dev/null")) filename = "nul"; - if (oflags & O_APPEND) + if ((oflags & O_APPEND) && !is_local_named_pipe_path(filename)) open_fn = mingw_open_append; else open_fn = _wopen; |