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,SPF_PASS 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 23040C433DB for ; Fri, 8 Jan 2021 11:15:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C3DBB239A1 for ; Fri, 8 Jan 2021 11:15:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726415AbhAHLPS convert rfc822-to-8bit (ORCPT ); Fri, 8 Jan 2021 06:15:18 -0500 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]:26597 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725806AbhAHLPR (ORCPT ); Fri, 8 Jan 2021 06:15:17 -0500 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-175-sD4VRU_TPyetWiPTPnISpQ-1; Fri, 08 Jan 2021 11:13:38 +0000 X-MC-Unique: sD4VRU_TPyetWiPTPnISpQ-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; Fri, 8 Jan 2021 11:13:37 +0000 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; Fri, 8 Jan 2021 11:13:37 +0000 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+q4Sa6RtPibF1KBcwErGHIAFWTS8sA= Date: Fri, 8 Jan 2021 11:13:37 +0000 Message-ID: <881cc102501e4c1a93785f0906dbd650@AcuMS.aculab.com> 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-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT 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've been looking at this code again now most of the pending changes are in Linus's tree. I was actually looking at going one stage further. The 'iov_iter' is always allocated with the 'iov_storage' *above). Usually both are on the callers stack - possibly in different functions. So add: struct iovec_iter { struct iov_iter iter; struct iovec to_free; struct iovec stack[UIO_FASTIOV]; }; int __iovec_import(struct iovec_iter *, const struct iovec __user *vec, unsigned long nr_segs, int type, bool compat); And a 'clean' function to do kfree(iovec->to_free); This reduces the complexity of most of the callers. I started doing the changes, but got in a mess in io_uring.c (as usual). I think I've got a patch pending (in my brain) to simplify the io_uring code. The plan is to add: if (iter->iov != xxx->to_free) iter->iov = xxx->stack; Prior to every use of the iter. This fixes up anything that got broken by a memcpy() of the fields. The tidyup code is then always kfree(xxx->to_free). David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)