Re: [PATCH v2] statx: optimize copy of struct statx to userspace

From	Eric Biggers <ebiggers3@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2] statx: optimize copy of struct statx to userspace
Date	2017-03-12 05:10 +0100
Message-ID	<tk2Zr-4xK-3@gated-at.bofh.it> (permalink)
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On Sun, Mar 12, 2017 at 02:29:27AM +0000, Al Viro wrote:
> 
> Oh, I agree that multiple __put_user() are wrong; I also agree that bulk copy is
> the right approach (when we get the unsafe stuff right, we can revisit that, but
> I suspect that on quite a few architectures a bulk copy will still give better
> time, no matter what).
> 
> > If padding is a concern at all (AFAICS it's not actually an issue now with
> > struct statx, but people tend to have different opinions on how careful they
> > want to be with padding), then I think we'll just have to start by memsetting
> > the whole struct to 0.
> 
> My point is simply that it's worth a comment in that code.

Okay, thanks.  I'll add a comment about the padding assumption, and I think I'll
take the suggestion to use a designated initializer.  Then at least all *fields*
get initialized by default.  And if in the future someone wants to conditionally
initialize fields, then they can use ?: or they can do it after the initializer.
Either way, at least they won't be able to forget to zero some field.

- Eric

Thread

[PATCH v2] statx: optimize copy of struct statx to userspace Eric Biggers <ebiggers3@gmail.com> - 2017-03-11 22:50 +0100
  Re: [PATCH v2] statx: optimize copy of struct statx to userspace Al Viro <viro@ZenIV.linux.org.uk> - 2017-03-12 02:30 +0100
    Re: [PATCH v2] statx: optimize copy of struct statx to userspace Eric Biggers <ebiggers3@gmail.com> - 2017-03-12 03:20 +0100
      Re: [PATCH v2] statx: optimize copy of struct statx to userspace Al Viro <viro@ZenIV.linux.org.uk> - 2017-03-12 03:40 +0100
        Re: [PATCH v2] statx: optimize copy of struct statx to userspace Eric Biggers <ebiggers3@gmail.com> - 2017-03-12 05:10 +0100
          Re: [PATCH v2] statx: optimize copy of struct statx to userspace Eric Biggers <ebiggers3@gmail.com> - 2017-03-12 07:10 +0100
            Re: [PATCH v2] statx: optimize copy of struct statx to userspace Andreas Dilger <adilger@dilger.ca> - 2017-03-13 05:40 +0100
              Re: [PATCH v2] statx: optimize copy of struct statx to userspace Florian Weimer <fweimer@redhat.com> - 2017-03-13 11:30 +0100
                Re: [PATCH v2] statx: optimize copy of struct statx to userspace Eric Biggers <ebiggers3@gmail.com> - 2017-03-13 19:20 +0100

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