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

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>,
	Maor Gottlieb <maorg@nvidia.com>, Daniel Vetter <daniel@ffwll.ch>,
	David Airlie <airlied@linux.ie>,
	Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>,
	dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org,
	Jani Nikula <jani.nikula@linux.intel.com>,
	Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
	linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Maxime Ripard <mripard@kernel.org>,
	Mike Marciniszyn <mike.marciniszyn@cornelisnetworks.com>,
	Rodrigo Vivi <rodrigo.vivi@intel.com>,
	Roland Scheidegger <sroland@vmware.com>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	VMware Graphics <linux-graphics-maintainer@vmware.com>,
	Yishai Hadas <yishaih@nvidia.com>, Zack Rusin <zackr@vmware.com>,
	Zhu Yanjun <zyjzyj2000@gmail.com>
Subject: Re: [PATCH rdma-next v2 1/2] lib/scatterlist: Fix wrong update of orig_nents
Date: Thu, 22 Jul 2021 14:07:51 +0100	[thread overview]
Message-ID: <YPltp39n9URglTXT@infradead.org> (raw)
In-Reply-To: <20210722130040.GH1117491@nvidia.com>

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.