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 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2E18DC47DA2 for ; Wed, 17 Jan 2024 14:28:10 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rQ6tF-0008CD-Uf; Wed, 17 Jan 2024 09:27:37 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rQ6tE-0008Bz-PV for qemu-devel@nongnu.org; Wed, 17 Jan 2024 09:27:36 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rQ6tC-0005oo-Me for qemu-devel@nongnu.org; Wed, 17 Jan 2024 09:27:36 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1705501653; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=7URkYapgNnSv0CJJDxOFDX2gRAQ5T3O93GtNU3lZSnk=; b=V5U5XqcG8lR05HDN5+LOo4EMtgEi/t+L0mCc/rZ7+J3xkAU45VrMyO5J1TE51gqbtjjTEt 8oyr8Kqmh+KclNkM642CnqHygI3PoZog4pmbztB/zXer//Uf1T5NhbaSqkTFcrNYngsPjB my3Oy6krXmzINqWIxdJ01lddcbUHbcQ= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-151-Qz1dHHI2PRiN6Bk0LNxhOw-1; Wed, 17 Jan 2024 09:27:31 -0500 X-MC-Unique: Qz1dHHI2PRiN6Bk0LNxhOw-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id AFFCD282D3DF; Wed, 17 Jan 2024 14:27:29 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.167]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 876123C27; Wed, 17 Jan 2024 14:27:28 +0000 (UTC) Date: Wed, 17 Jan 2024 14:27:26 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Fabiano Rosas , qemu-devel@nongnu.org, armbru@redhat.com, Juan Quintela , Peter Xu , Leonardo Bras , Claudio Fontana Subject: Re: [RFC PATCH v3 15/30] io: Add a pwritev/preadv version that takes a discontiguous iovec Message-ID: References: <20231127202612.23012-1-farosas@suse.de> <20231127202612.23012-16-farosas@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.10 (2023-03-25) X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.1 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -38 X-Spam_score: -3.9 X-Spam_bar: --- X-Spam_report: (-3.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.806, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Jan 17, 2024 at 12:39:26PM +0000, Daniel P. Berrangé wrote: > On Mon, Nov 27, 2023 at 05:25:57PM -0300, Fabiano Rosas wrote: > > For the upcoming support to fixed-ram migration with multifd, we need > > to be able to accept an iovec array with non-contiguous data. > > > > Add a pwritev and preadv version that splits the array into contiguous > > segments before writing. With that we can have the ram code continue > > to add pages in any order and the multifd code continue to send large > > arrays for reading and writing. > > > > Signed-off-by: Fabiano Rosas > > --- > > - split the API that was merged into a single function > > - use uintptr_t for compatibility with 32-bit > > --- > > include/io/channel.h | 26 ++++++++++++++++ > > io/channel.c | 70 ++++++++++++++++++++++++++++++++++++++++++++ > > 2 files changed, 96 insertions(+) > > > > diff --git a/include/io/channel.h b/include/io/channel.h > > index 7986c49c71..25383db5aa 100644 > > --- a/include/io/channel.h > > +++ b/include/io/channel.h > > @@ -559,6 +559,19 @@ int qio_channel_close(QIOChannel *ioc, > > ssize_t qio_channel_pwritev(QIOChannel *ioc, const struct iovec *iov, > > size_t niov, off_t offset, Error **errp); > > > > +/** > > + * qio_channel_pwritev_all: > > + * @ioc: the channel object > > + * @iov: the array of memory regions to write data from > > + * @niov: the length of the @iov array > > + * @offset: the iovec offset in the file where to write the data > > + * @errp: pointer to a NULL-initialized error object > > + * > > + * Returns: 0 if all bytes were written, or -1 on error > > + */ > > +int qio_channel_pwritev_all(QIOChannel *ioc, const struct iovec *iov, > > + size_t niov, off_t offset, Error **errp); > > + > > /** > > * qio_channel_pwrite > > * @ioc: the channel object > > @@ -595,6 +608,19 @@ ssize_t qio_channel_pwrite(QIOChannel *ioc, char *buf, size_t buflen, > > ssize_t qio_channel_preadv(QIOChannel *ioc, const struct iovec *iov, > > size_t niov, off_t offset, Error **errp); > > > > +/** > > + * qio_channel_preadv_all: > > + * @ioc: the channel object > > + * @iov: the array of memory regions to read data to > > + * @niov: the length of the @iov array > > + * @offset: the iovec offset in the file from where to read the data > > + * @errp: pointer to a NULL-initialized error object > > + * > > + * Returns: 0 if all bytes were read, or -1 on error > > + */ > > +int qio_channel_preadv_all(QIOChannel *ioc, const struct iovec *iov, > > + size_t niov, off_t offset, Error **errp); > > + > > /** > > * qio_channel_pread > > * @ioc: the channel object > > diff --git a/io/channel.c b/io/channel.c > > index a1f12f8e90..2f1745d052 100644 > > --- a/io/channel.c > > +++ b/io/channel.c > > @@ -472,6 +472,69 @@ ssize_t qio_channel_pwritev(QIOChannel *ioc, const struct iovec *iov, > > return klass->io_pwritev(ioc, iov, niov, offset, errp); > > } > > > > +static int qio_channel_preadv_pwritev_contiguous(QIOChannel *ioc, > > + const struct iovec *iov, > > + size_t niov, off_t offset, > > + bool is_write, Error **errp) > > +{ > > + ssize_t ret = -1; > > + int i, slice_idx, slice_num; > > + uintptr_t base, next, file_offset; > > + size_t len; > > + > > + slice_idx = 0; > > + slice_num = 1; > > + > > + /* > > + * If the iov array doesn't have contiguous elements, we need to > > + * split it in slices because we only have one (file) 'offset' for > > + * the whole iov. Do this here so callers don't need to break the > > + * iov array themselves. > > + */ > > + for (i = 0; i < niov; i++, slice_num++) { > > + base = (uintptr_t) iov[i].iov_base; > > + > > + if (i != niov - 1) { > > + len = iov[i].iov_len; > > + next = (uintptr_t) iov[i + 1].iov_base; > > + > > + if (base + len == next) { > > + continue; > > + } > > + } > > + > > + /* > > + * Use the offset of the first element of the segment that > > + * we're sending. > > + */ > > + file_offset = offset + (uintptr_t) iov[slice_idx].iov_base; > > + > > + if (is_write) { > > + ret = qio_channel_pwritev(ioc, &iov[slice_idx], slice_num, > > + file_offset, errp); > > + } else { > > + ret = qio_channel_preadv(ioc, &iov[slice_idx], slice_num, > > + file_offset, errp); > > + } > > iov_base is the address of a pointer in RAM, so could be > potentially any 64-bit value. > > We're assigning file_offset to this pointer address with an > user supplied offset, and then using it as an offset on disk. > First this could result in 64-bit overflow when 'offset' is > added to 'iov_base', and second this could result in a file > that's 16 Exabytes in size (with holes of course). > > I don't get how this is supposed to work, or be used ? I feel like this whole method might become clearer if we separated out the logic for merging memory adjacent iovecs. How about adding a 'iov_collapse' method in iov.h / iov.c to do the merging and then let the actual I/O code be simpler ? > > > + > > + if (ret < 0) { > > + break; > > + } > > + > > + slice_idx += slice_num; > > + slice_num = 0; > > + } > > + > > + return (ret < 0) ? -1 : 0; > > +} > > + > > +int qio_channel_pwritev_all(QIOChannel *ioc, const struct iovec *iov, > > + size_t niov, off_t offset, Error **errp) > > +{ > > + return qio_channel_preadv_pwritev_contiguous(ioc, iov, niov, > > + offset, true, errp); > > +} > > + > > ssize_t qio_channel_pwrite(QIOChannel *ioc, char *buf, size_t buflen, > > off_t offset, Error **errp) > > { > > @@ -501,6 +564,13 @@ ssize_t qio_channel_preadv(QIOChannel *ioc, const struct iovec *iov, > > return klass->io_preadv(ioc, iov, niov, offset, errp); > > } > > > > +int qio_channel_preadv_all(QIOChannel *ioc, const struct iovec *iov, > > + size_t niov, off_t offset, Error **errp) > > +{ > > + return qio_channel_preadv_pwritev_contiguous(ioc, iov, niov, > > + offset, false, errp); > > +} > > + > > ssize_t qio_channel_pread(QIOChannel *ioc, char *buf, size_t buflen, > > off_t offset, Error **errp) > > { > > -- > > 2.35.3 > > > > With regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| > > With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|