linux-kernel - Re: [PATCH v7 01/31] iov_iter: Add ITER

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Date:   Mon, 26 Apr 2021 19:52:49 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     David Howells <dhowells@...hat.com>
Cc:     linux-fsdevel@...r.kernel.org,
        Dave Wysochanski <dwysocha@...hat.com>,
        Marc Dionne <marc.dionne@...istor.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Christoph Hellwig <hch@....de>, linux-mm@...ck.org,
        linux-cachefs@...hat.com, linux-afs@...ts.infradead.org,
        linux-nfs@...r.kernel.org, linux-cifs@...r.kernel.org,
        ceph-devel@...r.kernel.org, v9fs-developer@...ts.sourceforge.net,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Steve French <sfrench@...ba.org>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Jeff Layton <jlayton@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 01/31] iov_iter: Add ITER_XARRAY

On Mon, Apr 26, 2021 at 08:23:31PM +0100, David Howells wrote:

> I really need to defer this question to Willy, but as I understand it,
> xas_retry() only restarts the current iteration.  Referring to the comment on
> xas_reset():
> 
>  * Resets the error or walk state of the @xas so future walks of the
>  * array will start from the root.  Use this if you have dropped the
>  * xarray lock and want to reuse the xa_state.
> 
> I think that the walk returns to the bottom of the tree and whilst xarray
> presents an interface that appears to be a contiguous array, it's actually a
> tree internally - and 'root' is the root of the tree, not the head of the
> array.
> 
> Basically, I think it throws away its cached iteration state - which might
> have been modified - and rewalks the tree to get back to the same index.

>From RTFS(lib/xarray.c) that looks right.  Nevermind the question, then...

Anyway, 

Reviewed-by: Al Viro <viro@...iv.linux.org.uk>

on the xarray-related bits (this patch + followups)