linux-kernel - Re: [V9fs-developer] [RFC] we should solve create-unlink-getattr idiom

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Date:   Fri, 9 Feb 2018 08:21:52 +0100
From:   Veaceslav Falico <veaceslav.falico@...wei.com>
To:     jiangyiwen <jiangyiwen@...wei.com>,
        Eric Van Hensbergen <ericvh@...il.com>,
        Greg Kurz <groug@...d.org>,
        <v9fs-developer@...ts.sourceforge.net>, <qemu-devel@...gnu.org>
CC:     <aneesh.kumar@...ux.vnet.ibm.com>,
        Ron Minnich <rminnich@...dia.gov>,
        Latchesar Ionkov <lucho@...kov.net>,
        <linux-kernel@...r.kernel.org>, <kernel-janitors@...r.kernel.org>
Subject: Re: [V9fs-developer] [RFC] we should solve create-unlink-getattr
 idiom

Hi Yiwen, all,

On 2/9/2018 8:10 AM, jiangyiwen wrote:
> Hi Eric and Greg,
> 
> I encountered the similar problem with create-unlink-getattr idiom.
> I use the testcase that create-unlink-setattr idiom, and I see the
> bug is reported at https://bugs.launchpad.net/qemu/+bug/1336794.
> Then I also see you already fix the issue and push the patch to upstream.
> https://github.com/ericvh/linux/commit/eaf70223eac094291169f5a6de580351890162a2
> http://patchwork.ozlabs.org/patch/626194/
> 
> Unfortunately, the two patches are not merged into master, I don't know
> the reason, so I suggest if the patche can be merged into master, and
> it will solve the create-unlink-getattr idiom.

As a follow up - the create-unlink-setattr (mainly ftruncate and anything
else which works on fd instead of path) isn't fixed by these patches, but
I'm currently working on a new patch, obviously on top of those two, to
make the setattr work too.

It's based on the same logic as the above patches though - use FIDs with
open fd's guest side and use open fd's host side if possible with f*
functions, otherwise path with l* functions.

It's bigger than the QEMU getattr patch, as there are no f* functions
available for ftruncate case, for example.

So if those two patches could be merged it'd be a lot easier to then
go forward with the setattr fix.

Thank you!

> 
> Thanks,
> Yiwen
> 
> .
>