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Date:   Thu, 22 Jul 2021 14:07:51 +0100
From:   Christoph Hellwig <hch@infradead.org>
To:     Jason Gunthorpe <jgg@nvidia.com>
Cc:     Leon Romanovsky <leon@kernel.org>,
        Doug Ledford <dledford@redhat.com>,
        Christoph Hellwig <hch@infradead.org>,
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        Zhu Yanjun <zyjzyj2000@gmail.com>
Subject: Re: [PATCH rdma-next v2 1/2] lib/scatterlist: Fix wrong update of
 orig_nents
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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.