linux-kernel - Re: [RFC PATCH 32/35] netfs: Add some more RMW support for ceph

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Message-ID: <3173770.1742484356@warthog.procyon.org.uk>
Date: Thu, 20 Mar 2025 15:25:56 +0000
From: David Howells <dhowells@...hat.com>
To: Viacheslav Dubeyko <Slava.Dubeyko@....com>
Cc: dhowells@...hat.com, Alex Markuze <amarkuze@...hat.com>,
    "slava@...eyko.com" <slava@...eyko.com>,
    "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
    "idryomov@...il.com" <idryomov@...il.com>,
    "jlayton@...nel.org" <jlayton@...nel.org>,
    "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
    "ceph-devel@...r.kernel.org" <ceph-devel@...r.kernel.org>,
    "dongsheng.yang@...ystack.cn" <dongsheng.yang@...ystack.cn>,
    "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 32/35] netfs: Add some more RMW support for ceph

Viacheslav Dubeyko <Slava.Dubeyko@....com> wrote:

> > +	rreq->buffer.iter	= *iter;
> 
> The struct iov_iter structure is complex enough and we assign it by value to
> rreq->buffer.iter. So, the initial pointer will not receive any changes
> then. Is it desired behavior here?

Yes.  The buffer described by the iterator is going to get partitioned across
a number of subrequests, each of which will get a copy of the iterator
suitably advanced and truncated.  As they may run in parallel, there's no way
for them to share the original iterator.

David