linux-kernel - Re: [PATCH rdma-next v1 1/2] lib/scatterlist: Fix wrong update of orig

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Message-ID: <2134e949-0569-c495-cb0b-f0324c5920df@nvidia.com>
Date:   Wed, 30 Jun 2021 12:14:04 +0300
From:   Maor Gottlieb <maorg@...dia.com>
To:     Christoph Hellwig <hch@...radead.org>,
        Leon Romanovsky <leon@...nel.org>
CC:     Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
        <linux-kernel@...r.kernel.org>, <linux-rdma@...r.kernel.org>,
        "Mike Marciniszyn" <mike.marciniszyn@...nelisnetworks.com>,
        Yishai Hadas <yishaih@...dia.com>,
        Zhu Yanjun <zyjzyj2000@...il.com>
Subject: Re: [PATCH rdma-next v1 1/2] lib/scatterlist: Fix wrong update of
 orig_nents

On 6/30/2021 10:16 AM, Christoph Hellwig wrote:
> On Wed, Jun 30, 2021 at 10:02:11AM +0300, Leon Romanovsky wrote:
>> Another possible solution is to change __sg_alloc_table()/__sg_alloc_table_from_pages
>> to return total_nents and expect from the users to store it internally and pass
>> it later to the __sg_free_table().
>>
>> Something like that.
> Yes, that sounds pretty reasonable.

OK. So we have two options

1. Add another argument (output) to __sg_alloc_table_from_pages and 
__sg_free_table.
     The thing is that __sg_free_table gets free_fn as argument while 
__sg_alloc_table_from_pages doesn't get alloc function. Users will pass 
NULL as free_fn and scatterlist internally will use sg_kfree.

2. Have dedicated functions to the appending allocations - 
sg_alloc_table_from_pages_append and sg_free_table_append. With this 
approach users that use __sg_alloc_table_from_pages not for appending 
allocation don't need to maintain the new argument.

Christoph, what do you prefer? do you see a better option?