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From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Thu, 18 Oct 2018 16:32:08 +0200
Message-ID: <CAJfpeguM-TU=nxj=T4t1DshniiEFBGq6yo+qo7Cx1QDnoNocMw@mail.gmail.com>
Subject: Re: [PATCH 2/3] uapi: get rid of STATX_ALL
To:     Florian Weimer <fw@deneb.enyo.de>
Cc:     Miklos Szeredi <mszeredi@redhat.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        Linux API <linux-api@vger.kernel.org>,
        David Howells <dhowells@redhat.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Andreas Dilger <adilger@dilger.ca>,
        Amir Goldstein <amir73il@gmail.com>
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On Thu, Oct 18, 2018 at 3:15 PM, Florian Weimer <fw@deneb.enyo.de> wrote:
> * Miklos Szeredi:
>
>>  #define STATX__RESERVED              0x80000000U     /* Reserved for future struct statx expansion */
>
> What about this?  Isn't it similar to STATX_ALL in the sense that we
> don't know yet what it will mean?

Kernel will return -EINVAL if request_mask contains STATX__RESERVED,
so it's definitely different from other flag values.

Specifying this in the UAPI sort of implies that other flag values
will *not* need a struct statx expansion, so it's safe to pass in any
random value not containing STATX__RESERVED on any past or future
kernel and it will not write beyond the current struct statx boundary.
Not sure if that's a useful thing or not, but it's not actively
harmful, like the STATX_ALL flag.

Thanks,
Miklos