From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 10FA7C43466 for ; Mon, 21 Sep 2020 14:50:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D8B39221EC for ; Mon, 21 Sep 2020 14:50:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727062AbgIUOuH convert rfc822-to-8bit (ORCPT ); Mon, 21 Sep 2020 10:50:07 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:24702 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726584AbgIUOuH (ORCPT ); Mon, 21 Sep 2020 10:50:07 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-86-4QhIQ9m2OJi1xwkLWjnc0A-1; Mon, 21 Sep 2020 15:50:02 +0100 X-MC-Unique: 4QhIQ9m2OJi1xwkLWjnc0A-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Mon, 21 Sep 2020 15:50:01 +0100 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Mon, 21 Sep 2020 15:50:01 +0100 From: David Laight To: 'Christoph Hellwig' CC: "linux-kernel@vger.kernel.org" , "netdev@vger.kernel.org" , "io-uring@vger.kernel.org" , Jens Axboe , "David S. Miller" , Al Viro , linux-fsdevel Subject: RE: [PATCH 5/9 next] scsi: Use iovec_import() instead of import_iovec(). Thread-Topic: [PATCH 5/9 next] scsi: Use iovec_import() instead of import_iovec(). Thread-Index: AdaLbdBrrJnvb+q4Sa6RtPibF1KBcwErGHIAAAK0UcA= Date: Mon, 21 Sep 2020 14:50:01 +0000 Message-ID: References: <27be46ece36c42d6a7dabf62c6ac7a98@AcuMS.aculab.com> <20200921142204.GE24515@infradead.org> In-Reply-To: <20200921142204.GE24515@infradead.org> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org From: Christoph Hellwig > Sent: 21 September 2020 15:22 > > So looking at the various callers I'm not sure this API is the > best. If we want to do something fancy I'd hide the struct iovec > instances entirely with something like: > > struct iov_storage { > struct iovec stack[UIO_FASTIOV], *vec; > } > > int iov_iter_import_iovec(struct iov_iter *iter, struct iov_storage *s, > const struct iovec __user *vec, unsigned long nr_segs, > int type); > > and then add a new helper to free the thing if needed: > > void iov_iter_release_iovec(struct iov_storage *s) > { > if (s->vec != s->stack) > kfree(s->vec); > } I didn't think of going that far. There are 2 call sites (in scsi) that don't pass the cache. Given that the 'buffer to free' address probably needs to be spilled to stack forcing in into an on-stack structure that is already passed by address is probably a good idea. The iov_iter_release_iovec() should be static inline and just: if (s->vec) kfree(s->vec); You want the test because 99.99% of the time it will be NULL. The kernel iov[] to use is iter.iov not part of the cache. That will be a bigger change on the io_uring code. (The patch I didn't write.) David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)