Re: [PATCH v4] statx: optimize copy of struct statx to userspace

From	David Howells <dhowells@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v4] statx: optimize copy of struct statx to userspace
Date	2017-03-16 12:50 +0100
Message-ID	<tlC4O-684-9@gated-at.bofh.it> (permalink)
References	<tkGNb-7uk-9@gated-at.bofh.it>
Organization	Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903

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Eric Biggers <ebiggers3@gmail.com> wrote:

> stat() instead initializes its struct on the stack and copies it to
> userspace with a single call to copy_to_user().  This turns out to be
> much faster, and changing statx to do this makes it almost as fast as
> stat:

I wonder if we actually need to copy __spare2 at the end.  We could define any
future values added in there to be unset/undefined if the respective bits are
not set.

I would prefer it to be cleaner, however, and clear the unused space.

Another thought is does it make sense to rearrange struct kstat to mirror
the first part of struct statx so that this can be memcpy'd?

David

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Re: [PATCH v4] statx: optimize copy of struct statx to userspace David Howells <dhowells@redhat.com> - 2017-03-16 12:50 +0100
  Re: [PATCH v4] statx: optimize copy of struct statx to userspace Eric Biggers <ebiggers3@gmail.com> - 2017-03-24 22:10 +0100

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