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
