Re: [PATCH v2 6/5] statx: add STATX_RESULT_MASK flag

[Andreas Dilger <adilger@dilger.ca>]

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On Oct 19, 2018, at 11:42 AM, Miklos Szeredi <miklos@szeredi.hu> wrote:
>>> +#define STATX_RESULT_MASK STATX__RESERVED
>> 
>> Please don't use that bit.
> 
> Using it internally is perfectly harmless.   If we'll need to extend
> statx in the future and make use of this flag externally, then we can
> easily move the internal flag somewhere else (e.g. extend request_mask
> to 64bit, which we'll probably need to do anyway in that case).

I was thinking about this - what is the point of returning an error
if STATX__RESERVED is set?  If this is used to indicate the presence
of e.g. stx_mask2, then newer applications trying to request any of the
flags encoded into stx_mask2 will get an error, rather than the expected
behaviour of "ignore flags you don't understand, and don't set them in
the return stx_mask".

Essentially, this will make STATX__RESERVED useless in the future, since
no application will be able to use it without getting an error if they
are running on an old kernel.

Cheers, Andreas






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