From: Johannes Sixt Date: Sat, 08 Sep 2018 18:31:45 GMT Subject: Re: [PATCH 2/2] mingw: fix mingw_open_append to work with named pipes Message-ID: In-Reply-To: <1c524f56-2021-a961-168f-e5c6d7914ec2@kdbg.org> Am 08.09.2018 um 11:26 schrieb Johannes Sixt: > Am 07.09.2018 um 20:19 schrieb Jeff Hostetler via GitGitGadget: >> diff --git a/compat/mingw.c b/compat/mingw.c >> index 858ca14a57..ef03bbe5d2 100644 >> --- a/compat/mingw.c >> +++ b/compat/mingw.c >> @@ -355,7 +355,7 @@ static int mingw_open_append(wchar_t const >> *wfilename, int oflags, ...) >>        * FILE_SHARE_WRITE is required to permit child processes >>        * to append to the file. >>        */ >> -    handle = CreateFileW(wfilename, FILE_APPEND_DATA, >> +    handle = CreateFileW(wfilename, FILE_WRITE_DATA | FILE_APPEND_DATA, >>               FILE_SHARE_WRITE | FILE_SHARE_READ, >>               NULL, create, FILE_ATTRIBUTE_NORMAL, NULL); >>       if (handle == INVALID_HANDLE_VALUE) >> > > I did not go with this version because the documentation > https://docs.microsoft.com/en-us/windows/desktop/fileio/file-access-rights-constants > says: > > FILE_APPEND_DATA: For a file object, the right to append data to the > file. (For local files, write operations will not overwrite existing > data if this flag is specified without FILE_WRITE_DATA.) [...] > > which could be interpreted as: Only if FILE_WRITE_DATA is not set, we > have the guarantee that existing data in local files is not overwritten, > i.e., new data is appended atomically. > > Is this interpretation too narrow and we do get atomicity even when > FILE_WRITE_DATA is set? Here is are some comments on stackoverflow which let me think that FILE_APPEND_DATA with FILE_WRITE_DATA is no longer atomic: https://stackoverflow.com/questions/20093571/difference-between-file-write-data-and-file-append-data#comment29995346_20108249 -- Hannes