From: Jeff Hostetler <jeffhost@xxxxxxxxxxxxx> Signed-off-by: Jeff Hostetler <jeffhost@xxxxxxxxxxxxx> --- compat/mingw.c | 38 ++++++++++++++++++++++++++++++++--- t/t0051-windows-named-pipe.sh | 2 +- 2 files changed, 36 insertions(+), 4 deletions(-) diff --git a/compat/mingw.c b/compat/mingw.c index 858ca14a57..f87376b26a 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 +386,23 @@ static int mingw_open_append(wchar_t const *wfilename, int oflags, ...) return fd; } +#define IS_SBS(ch) (((ch) == '/') || ((ch) == '\\')) +/* + * Does the pathname map to the local named pipe filesystem? + * That is, does it have a "//./pipe/" prefix? + */ +static int mingw_is_local_named_pipe_path(const char *filename) +{ + return (IS_SBS(filename[0]) && + IS_SBS(filename[1]) && + filename[2] == '.' && + IS_SBS(filename[3]) && + !strncasecmp(filename+4, "pipe", 4) && + IS_SBS(filename[8]) && + filename[9]); +} +#undef IS_SBS + int mingw_open (const char *filename, int oflags, ...) { typedef int (*open_fn_t)(wchar_t const *wfilename, int oflags, ...); @@ -387,7 +419,7 @@ int mingw_open (const char *filename, int oflags, ...) if (filename && !strcmp(filename, "/dev/null")) filename = "nul"; - if (oflags & O_APPEND) + if ((oflags & O_APPEND) && !mingw_is_local_named_pipe_path(filename)) open_fn = mingw_open_append; else open_fn = _wopen; diff --git a/t/t0051-windows-named-pipe.sh b/t/t0051-windows-named-pipe.sh index e3c36341a0..10ac92d225 100755 --- a/t/t0051-windows-named-pipe.sh +++ b/t/t0051-windows-named-pipe.sh @@ -4,7 +4,7 @@ test_description='Windows named pipes' . ./test-lib.sh -test_expect_failure MINGW 'o_append write to named pipe' ' +test_expect_success MINGW 'o_append write to named pipe' ' GIT_TRACE="$(pwd)/expect" git status >/dev/null 2>&1 && { test-tool windows-named-pipe t0051 >actual 2>&1 & } && pid=$! && -- gitgitgadget
