Quoting Paolo Bonzini (2015-11-11 08:49:57) > > > 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
Yah, both are more proper actually (I was relying on FILE_GENERIC_READ already containing the other flags from FILE_GENERIC_WRITE, but that's more likely to break in the future). I think I prefer the former since it avoids confusion on GENERIC_READ vs. FILE_GENERIC_READ differences. Kirk, I'm planning on squashing this into your v2 series, so no need to resubmit. Thanks! > > ? > > Paolo >
