Received-SPF: Pass (protection.outlook.com: domain of nvidia.com designates
 216.228.117.161 as permitted sender) receiver=protection.outlook.com;
 client-ip=216.228.117.161; helo=mail.nvidia.com; pr=C
Message-ID: <4be974aa-2beb-9ae5-3f48-7dde6241b0c7@nvidia.com>
Date:   Tue, 24 Jan 2023 12:50:18 -0800
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.6.1
Subject: Re: [PATCH v9 2/8] iov_iter: Add a function to extract a page list
 from an iterator
Content-Language: en-US
To:     David Howells <dhowells@redhat.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Christoph Hellwig <hch@infradead.org>
CC:     Matthew Wilcox <willy@infradead.org>, Jens Axboe <axboe@kernel.dk>,
        "Jan Kara" <jack@suse.cz>, Jeff Layton <jlayton@kernel.org>,
        David Hildenbrand <david@redhat.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Logan Gunthorpe <logang@deltatee.com>,
        <linux-fsdevel@vger.kernel.org>, <linux-block@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, "Christoph Hellwig" <hch@lst.de>,
        <linux-mm@kvack.org>
References: <20230124170108.1070389-1-dhowells@redhat.com>
 <20230124170108.1070389-3-dhowells@redhat.com>
From:   John Hubbard <jhubbard@nvidia.com>
In-Reply-To: <20230124170108.1070389-3-dhowells@redhat.com>
Content-Type: text/plain; charset="UTF-8"; format=flowed
Content-Transfer-Encoding: 7bit
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 24 Jan 2023 20:50:29.8128
 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: 3c8554d5-0b05-4f59-f95a-08dafe4ca112
X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a
X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.161];Helo=[mail.nvidia.com]
X-MS-Exchange-CrossTenant-AuthSource: DM6NAM11FT034.eop-nam11.prod.protection.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Anonymous
X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem
X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ2PR12MB7991
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 1/24/23 09:01, David Howells wrote:
...
> +/*
> + * Extract a list of contiguous pages from an ITER_BVEC iterator.  This does
> + * not get references on the pages, nor does it get a pin on them.
> + */
> +static ssize_t iov_iter_extract_bvec_pages(struct iov_iter *i,
> +					   struct page ***pages, size_t maxsize,
> +					   unsigned int maxpages,
> +					   unsigned int extraction_flags,
> +					   size_t *offset0)
> +{
> +	struct page **p, *page;
> +	size_t skip = i->iov_offset, offset;
> +	int k;
> +
> +	for (;;) {
> +		if (i->nr_segs == 0)
> +			return 0;
> +		maxsize = min(maxsize, i->bvec->bv_len - skip);
> +		if (maxsize)
> +			break;
> +		i->iov_offset = 0;
> +		i->nr_segs--;
> +		i->kvec++;
> +		skip = 0;
> +	}
> +
> +	skip += i->bvec->bv_offset;
> +	page = i->bvec->bv_page + skip / PAGE_SIZE;
> +	offset = skip % PAGE_SIZE;
> +	*offset0 = offset;
> +
> +	maxpages = want_pages_array(pages, maxsize, offset, maxpages);
> +	if (!maxpages)
> +		return -ENOMEM;

Is it OK that the iov_iter position has been advanced, and left that way,
in the case of an early -ENOMEM return here?


thanks,
-- 
John Hubbard
NVIDIA