linux-kernel - Re: [RFC PATCH 12/53] netfs: Provide tools to create a buffer in an xarray

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Message-ID: <1709498.1700251890@warthog.procyon.org.uk>
Date:   Fri, 17 Nov 2023 20:11:30 +0000
From:   David Howells <dhowells@...hat.com>
To:     Jeff Layton <jlayton@...nel.org>
Cc:     dhowells@...hat.com, Steve French <smfrench@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        Marc Dionne <marc.dionne@...istor.com>,
        Paulo Alcantara <pc@...guebit.com>,
        Shyam Prasad N <sprasad@...rosoft.com>,
        Tom Talpey <tom@...pey.com>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Ilya Dryomov <idryomov@...il.com>,
        Christian Brauner <christian@...uner.io>,
        linux-afs@...ts.infradead.org, linux-cifs@...r.kernel.org,
        linux-nfs@...r.kernel.org, ceph-devel@...r.kernel.org,
        v9fs@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-cachefs@...hat.com
Subject: Re: [RFC PATCH 12/53] netfs: Provide tools to create a buffer in an xarray

Jeff Layton <jlayton@...nel.org> wrote:

> Some kerneldoc comments on these new helpers would be nice. I assume
> that "index" and "to" are "start" and "end" for this, but it'd be nice
> to make that explicit.

These are internal to netfs not API functions, so they shouldn't appear in the
API docs.  That's why the declaration is in internal.h, not netfs.h.

That said, I could describe them better.

> > +	ret = netfs_add_folios_to_buffer(buffer, mapping, want_index,
> > +					 have_index - 1, gfp_mask);
> > +	if (ret < 0)
> > +		return ret;
> > +	have_folios += have_index - want_index;
> > +
> > +	ret = netfs_add_folios_to_buffer(buffer, mapping,
> > +					 have_index + have_folios,
> > +					 want_index + want_folios - 1,
> > +					 gfp_mask);
> 
> I don't get it. Why are you calling netfs_add_folios_to_buffer twice
> here? Why not just make one call? Either way, a comment here explaining
> that would also be nice.

The ranges aren't contiguous.  They bracket the folios spliced from the
mapping.  That being said, I seem to have lost a bit of maths somewhere.

Further, I'm not now using netfs_add_folios_to_buffer(), so I'll remove it.

David