linux-kernel - Re: How to convert I/O iterators to iterators, sglists and RDMA lists

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Message-ID: <1014264.1667587643@warthog.procyon.org.uk>
Date:   Fri, 04 Nov 2022 18:47:23 +0000
From:   David Howells <dhowells@...hat.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     dhowells@...hat.com, Christoph Hellwig <hch@...radead.org>,
        willy@...radead.org, dchinner@...hat.com,
        Steve French <smfrench@...il.com>,
        Shyam Prasad N <nspmangalore@...il.com>,
        Rohith Surabattula <rohiths.msft@...il.com>,
        Jeff Layton <jlayton@...nel.org>,
        Ira Weiny <ira.weiny@...el.com>, torvalds@...ux-foundation.org,
        linux-cifs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, jlayton@...hat.com
Subject: Re: How to convert I/O iterators to iterators, sglists and RDMA lists

David Howells <dhowells@...hat.com> wrote:

> > What protects pages involved in ITER_XARRAY iterator created by
> > afs_read_dir()?  Note that we are not guaranteed inode_lock() on
> > the directory in question...
> 
> Yeah - that needs fixing.  The size of the data can change, but I don't update
> the iterator.

Actually, no.  The iterator is the output buffer for afs_fetch_data().  If the
buffer turned out to be too small we drop the validate_lock and go round and
try again.

req->actual_len and req->file_size are updated by afs_fetch_data() from the
RPC reply.  req->len tells the RPC delivery code how big the buffer is (which
we don't have to fill if there's less data available than we have buffer
space).

David