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spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:35354 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kxUe4-0002mS-5t for qemu-devel@archiver.kernel.org; Thu, 07 Jan 2021 07:44:04 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:46924) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kxUcb-0001jG-NC for qemu-devel@nongnu.org; Thu, 07 Jan 2021 07:42:33 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:34052) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kxUcY-0005CF-7W for qemu-devel@nongnu.org; Thu, 07 Jan 2021 07:42:33 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1610023348; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=x2/pXQXkDLe0IEu+TVXZjPsAia6NL/gehZzIzBouQuE=; b=W1Q6dP6533MDJp23F2cMqCTgyBQVBo5tInt1LzmVEOFpc6FLafSFAbRRR8mpOmqEwoUGYx f/mvsUzvdHxRNu0t+SF5tz81yhU9PL9gMYsUVqG3YQLZb0kyW0NF2QNC8SSilxbM6MN0hk WUDzg6YburZSLdOqg2VCW806g5CnvQU= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-185-0vEIdz09Oj6BqXCD-D2qiQ-1; Thu, 07 Jan 2021 07:42:25 -0500 X-MC-Unique: 0vEIdz09Oj6BqXCD-D2qiQ-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 27A8B803622; Thu, 7 Jan 2021 12:42:24 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-114-252.ams2.redhat.com [10.36.114.252]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2B7B810013BD; Thu, 7 Jan 2021 12:42:18 +0000 (UTC) Subject: Re: [PATCH v3 2/5] file-posix: add sg_get_max_segments that actually works with sg To: Maxim Levitsky , qemu-devel@nongnu.org References: <20201217165612.942849-1-mlevitsk@redhat.com> <20201217165612.942849-3-mlevitsk@redhat.com> From: Max Reitz Message-ID: <5f05e682-157c-424e-6284-604bb964147b@redhat.com> Date: Thu, 7 Jan 2021 13:42:16 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <20201217165612.942849-3-mlevitsk@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mreitz@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=mreitz@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -32 X-Spam_score: -3.3 X-Spam_bar: --- X-Spam_report: (-3.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.246, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.267, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Fam Zheng , Ronnie Sahlberg , qemu-block@nongnu.org, Peter Lieven , Tom Yan , Stefan Hajnoczi , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 17.12.20 17:56, Maxim Levitsky wrote: > From: Tom Yan > > sg devices have different major/minor than their corresponding > block devices. Using sysfs to get max segments never really worked > for them. > > Fortunately the sg driver provides an ioctl to get sg_tablesize, > which is apparently equivalent to max segments. > > Signed-off-by: Tom Yan > Signed-off-by: Maxim Levitsky > --- > block/file-posix.c | 22 +++++++++++++++++++++- > 1 file changed, 21 insertions(+), 1 deletion(-) > > diff --git a/block/file-posix.c b/block/file-posix.c > index cbf1271773..2bf4d095a7 100644 > --- a/block/file-posix.c > +++ b/block/file-posix.c > @@ -1179,6 +1179,26 @@ static int sg_get_max_transfer_length(int fd) > #endif > } > > +static int sg_get_max_segments(int fd) > +{ > + /* > + * /dev/sg* character devices report 'max_segments' via > + * SG_GET_SG_TABLESIZE ioctl > + */ > + > +#ifdef SG_GET_SG_TABLESIZE > + long max_segments = 0; > + > + if (ioctl(fd, SG_GET_SG_TABLESIZE, &max_segments) == 0) { As far as I can tell from googling, SG_GET_SG_TABLESIZE takes an int pointer. Apart from that, looks good. Max > + return max_segments; > + } else { > + return -errno; > + } > +#else > + return -ENOSYS; > +#endif > +} > + > static int get_max_transfer_length(int fd) > { > #if defined(BLKSECTGET) > @@ -1265,7 +1285,7 @@ static void hdev_refresh_limits(BlockDriverState *bs, Error **errp) > bs->bl.max_transfer = pow2floor(ret); > } > > - ret = get_max_segments(s->fd); > + ret = bs->sg ? sg_get_max_segments(s->fd) : get_max_segments(s->fd); > if (ret > 0) { > bs->bl.max_transfer = MIN_NON_ZERO(bs->bl.max_transfer, > ret * qemu_real_host_page_size); >