From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37895) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZwWj7-0006Fj-2h for qemu-devel@nongnu.org; Wed, 11 Nov 2015 09:50:29 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZwWj0-0003uR-J0 for qemu-devel@nongnu.org; Wed, 11 Nov 2015 09:50:21 -0500 Sender: Paolo Bonzini References: <1447105745-32358-1-git-send-email-kallan@suse.com> <20151110154059.25378.38107@loki> <56423076.5020408@redhat.com> <20151111140208.31702.72506@loki> From: Paolo Bonzini Message-ID: <56435595.7010704@redhat.com> Date: Wed, 11 Nov 2015 15:49:57 +0100 MIME-Version: 1.0 In-Reply-To: <20151111140208.31702.72506@loki> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] qga: fix append file open modes for win32 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Michael Roth , Kirk Allan , qemu-devel@nongnu.org Cc: qemu-stable@nongnu.org On 11/11/2015 15:02, Michael Roth wrote: >> GENERIC_READ for files >> = FILE_READ_DATA >> + FILE_READ_ATTRIBUTES >> + FILE_READ_EA >> + SYNCHRONIZE >> + STANDARD_RIGHTS_READ (which is READ_CONTROL) >> >> GENERIC_WRITE for files >> = FILE_APPEND_DATA >> + FILE_WRITE_DATA >> + FILE_WRITE_ATTRIBUTES >> + FILE_WRITE_EA >> + SYNCHRONIZE >> + STANDARD_RIGHTS_WRITE (which is READ_CONTROL too!) >> >> Of these of course qemu-ga only needs FILE_*_DATA and possibly SYNCHRONIZE. >> >> The above description doesn't say what happens if you specify >> FILE_READ_DATA and FILE_APPEND_DATA together, but I guess you can expect >> it to just work. > > Thanks, this is very helpful. This seems to coincide with > FILE_GENERIC_WRITE / FILE_GENERIC_READ if you want to access the > bitmasks directly (though it looks like you can still add flags > to GENERIC_WRITE / GENERIC_READ): > > https://msdn.microsoft.com/en-us/library/windows/desktop/aa364399(v=vs.85).aspx Yes, I had missed the FILE_GENERIC_* definitions. I found them now in mingw as well, and they are exactly what you would expect (an | of the various flags). > Looks like the crux of it is that FILE_WRITE_DATA causes us not to ignore > the start offset (0) for writes, so we end up writing data at the > beginning of the file instead of the end. > > So I think the following > should work: > > a: FILE_GENERIC_WRITE & ~FILE_WRITE_DATA > a+: FILE_GENERIC_READ | FILE_APPEND_DATA > > FILE_APPEND_DATA by itself might work for a:, but for consistency I > think I'd prefer sticking with the generic set and masking out > FILE_WRITE_DATA. For a+ I would use any of (FILE_GENERIC_READ | FILE_GENERIC_WRITE) & ~FILE_WRITE_DATA GENERIC_READ | (FILE_GENERIC_WRITE & ~FILE_WRITE_DATA) Perhaps you can define this: #define FILE_GENERIC_APPEND (FILE_GENERIC_WRITE & ~FILE_WRITE_DATA) and then use a: FILE_GENERIC_APPEND a+: GENERIC_READ|FILE_GENERIC_APPEND or a: FILE_GENERIC_APPEND a+: FILE_GENERIC_READ|FILE_GENERIC_APPEND ? Paolo