From patchwork Thu Aug 12 08:41:45 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Hanna Czenczek X-Patchwork-Id: 12432881 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=-13.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 6E684C4338F for ; Thu, 12 Aug 2021 08:44:04 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id CFBA76103A for ; Thu, 12 Aug 2021 08:44:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org CFBA76103A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:38300 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mE6Jm-0007rL-M2 for qemu-devel@archiver.kernel.org; Thu, 12 Aug 2021 04:44:02 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:35574) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mE6Hr-0004fm-5c for qemu-devel@nongnu.org; Thu, 12 Aug 2021 04:42:03 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:46234) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mE6Hp-0004hT-62 for qemu-devel@nongnu.org; Thu, 12 Aug 2021 04:42:02 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1628757719; 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=AJc/JbhYorjEy4i7jmhVfBMpq2Saco4d+IvoYw2Dqps=; b=TS9hSyGqlcTVLVrkbFjLDUvP48D+B8CAmFfGrh30Ew6Y0peUHOwK9YGsR3dcjwzrlUyTZz VSX0PDiNg/2WiRsJLQkKqSlbRUrl1Cv3XFM9wiS23Ry1QWti5g/pI4uVh5viyELmRjdJdi D/2YQGwKRUIQOsH38mLlYsAgXHnbRP8= 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-20-AubHUzSAOs6GytN2BhLrtg-1; Thu, 12 Aug 2021 04:41:57 -0400 X-MC-Unique: AubHUzSAOs6GytN2BhLrtg-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E5FE7190B2A2; Thu, 12 Aug 2021 08:41:56 +0000 (UTC) Received: from localhost (unknown [10.39.193.89]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8CB9A4536; Thu, 12 Aug 2021 08:41:56 +0000 (UTC) From: Hanna Reitz To: qemu-block@nongnu.org Subject: [PATCH v3 3/6] block: Clarify that @bytes is no limit on *pnum Date: Thu, 12 Aug 2021 10:41:45 +0200 Message-Id: <20210812084148.14458-4-hreitz@redhat.com> In-Reply-To: <20210812084148.14458-1-hreitz@redhat.com> References: <20210812084148.14458-1-hreitz@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=hreitz@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Received-SPF: pass client-ip=170.10.133.124; envelope-from=hreitz@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -15 X-Spam_score: -1.6 X-Spam_bar: - X-Spam_report: (-1.6 / 5.0 requ) DKIMWL_WL_HIGH=-0.7, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham 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 , Hanna Reitz , Vladimir Sementsov-Ogievskiy , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" .bdrv_co_block_status() implementations are free to return a *pnum that exceeds @bytes, because bdrv_co_block_status() in block/io.c will clamp *pnum as necessary. On the other hand, if drivers' implementations return values for *pnum that are as large as possible, our recently introduced block-status cache will become more effective. So, make a note in block_int.h that @bytes is no upper limit for *pnum. Suggested-by: Eric Blake Signed-off-by: Hanna Reitz Reviewed-by: Vladimir Sementsov-Ogievskiy Reviewed-by: Eric Blake --- include/block/block_int.h | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/include/block/block_int.h b/include/block/block_int.h index 437d746733..5451f89b8d 100644 --- a/include/block/block_int.h +++ b/include/block/block_int.h @@ -348,6 +348,15 @@ struct BlockDriver { * clamped to bdrv_getlength() and aligned to request_alignment, * as well as non-NULL pnum, map, and file; in turn, the driver * must return an error or set pnum to an aligned non-zero value. + * + * Note that @bytes is just a hint on how big of a region the + * caller wants to inspect. It is not a limit on *pnum. + * Implementations are free to return larger values of *pnum if + * doing so does not incur a performance penalty. + * + * block/io.c's bdrv_co_block_status() will utilize an unclamped + * *pnum value for the block-status cache on protocol nodes, prior + * to clamping *pnum for return to its caller. */ int coroutine_fn (*bdrv_co_block_status)(BlockDriverState *bs, bool want_zero, int64_t offset, int64_t bytes, int64_t *pnum,