linux-kernel - Re: [PATCH rdma-next v2 1/2] lib/scatterlist: Fix wrong update of orig

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Date:   Thu, 22 Jul 2021 14:07:51 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Leon Romanovsky <leon@...nel.org>,
        Doug Ledford <dledford@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        Maor Gottlieb <maorg@...dia.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
        dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Mike Marciniszyn <mike.marciniszyn@...nelisnetworks.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Roland Scheidegger <sroland@...are.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        VMware Graphics <linux-graphics-maintainer@...are.com>,
        Yishai Hadas <yishaih@...dia.com>,
        Zack Rusin <zackr@...are.com>,
        Zhu Yanjun <zyjzyj2000@...il.com>
Subject: Re: [PATCH rdma-next v2 1/2] lib/scatterlist: Fix wrong update of
 orig_nents

On Thu, Jul 22, 2021 at 10:00:40AM -0300, Jason Gunthorpe wrote:
> this is better:
> 
>    struct sg_append_table state;
> 
>    sg_append_init(&state, sgt, gfp_mask);
> 
>    while (..)
>      ret = sg_append_pages(&state, pages, n_pages, ..)
>      if (ret)
> 	 sg_append_abort(&state); // Frees the sgt and puts it to NULL
>    sg_append_complete(&state)
> 
> Which allows sg_alloc_table_from_pages() to be written as
> 
>    struct sg_append_table state;
>    sg_append_init(&state, sgt, gfp_mask);
>    ret = sg_append_pages(&state,pages, n_pages, offset, size, UINT_MAX)
>    if (ret) {
>       sg_append_abort(&state);
>       return ret;
>    }
>    sg_append_complete(&state);
>    return 0;
> 
> And then the API can manage all of this in some sane and
> understandable way.

That would be a lot easier to use for sure.  Not sure how invasive the
changes would be, though.