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 AD56EC3ABBE for ; Thu, 8 May 2025 05:04:41 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uCtQH-00021g-Gl; Thu, 08 May 2025 01:03:53 -0400 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 1uCtQG-0001zU-24 for qemu-devel@nongnu.org; Thu, 08 May 2025 01:03:52 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1uCtQE-0008LH-GF for qemu-devel@nongnu.org; Thu, 08 May 2025 01:03:51 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1746680629; 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: in-reply-to:in-reply-to:references:references; bh=0S89U0uoChOkurY3P2kOs9ldxrPsCMbF+eT2LnKHcnc=; b=YPz64DbsOMd2HfbCESz6y7JgdQTpBx0+iQS8BhnKnnb0lHaB+V61chhovptKf08/0uQcO9 cIr6va/Zwo2ra4oUpfr7vATut4CoDCHSSTn82PToV+Mbl/wgxn5Djgms1Z1dtMv9zL/E8y 0BS/qzCfPREGb2NinhcGxydPyaD0bV4= Received: from mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-46-iA1yHJ5fOPqJVSNhfr2-wQ-1; Thu, 08 May 2025 01:03:47 -0400 X-MC-Unique: iA1yHJ5fOPqJVSNhfr2-wQ-1 X-Mimecast-MFC-AGG-ID: iA1yHJ5fOPqJVSNhfr2-wQ_1746680626 Received: from mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.15]) (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 mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 30E071956087; Thu, 8 May 2025 05:03:46 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.45.242.27]) by mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id C23001955F24; Thu, 8 May 2025 05:03:45 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id CAA4721E66C3; Thu, 08 May 2025 07:03:42 +0200 (CEST) From: Markus Armbruster To: Nir Soffer Cc: qemu-devel@nongnu.org, Eric Blake , qemu-block@nongnu.org, Kevin Wolf , Fam Zheng , Hanna Reitz Subject: Re: [PATCH v2 1/2] block/null: Report DATA if not reading zeroes In-Reply-To: <87plgjg1kh.fsf@pond.sub.org> (Markus Armbruster's message of "Thu, 08 May 2025 06:37:34 +0200") References: <20250430203717.16359-1-nirsof@gmail.com> <20250430203717.16359-2-nirsof@gmail.com> <87plgjg1kh.fsf@pond.sub.org> Date: Thu, 08 May 2025 07:03:42 +0200 Message-ID: <87wmarelsh.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.414, 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_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Markus Armbruster writes: > Nir Soffer writes: > >> If read-zeroes is not set, we did not report BDRV_BLOCK_DATA or >> BDRV_BLOCK_ZERO. This is not consistent with other drivers and can >> confuse users or other programs: >> >> % qemu-img map --output json "json:{'driver': 'raw', 'file': {'driver': 'null-co', 'size': '1g'}}" >> [{ "start": 0, "length": 1073741824, "depth": 0, "present": false, "zero": false, "data": false, "compressed": false}] >> >> % qemu-nbd "json:{'driver': 'raw', 'file': {'driver': 'null-co', 'size': '1g'}}" & >> >> % nbdinfo --map nbd://127.0.0.1 >> 0 1073741824 1 hole >> >> With this change we report DATA in this case: >> >> % ./qemu-img map --output json "json:{'driver': 'raw', 'file': {'driver': 'null-co', 'size': '1g'}}" >> [{ "start": 0, "length": 1073741824, "depth": 0, "present": true, "zero": false, "data": true, "compressed": false, "offset": 0}] >> >> % ./qemu-nbd "json:{'driver': 'raw', 'file': {'driver': 'null-co', 'size': '1g'}}" & >> >> % nbdinfo --map nbd://127.0.0.1 >> 0 1073741824 0 data >> >> Signed-off-by: Nir Soffer >> --- >> block/null.c | 4 +--- >> qapi/block-core.json | 5 +++-- >> 2 files changed, 4 insertions(+), 5 deletions(-) >> >> diff --git a/block/null.c b/block/null.c >> index dc0b1fdbd9..7ba87bd9a9 100644 >> --- a/block/null.c >> +++ b/block/null.c >> @@ -239,9 +239,7 @@ static int coroutine_fn null_co_block_status(BlockDriverState *bs, >> *map = offset; >> *file = bs; >> >> - if (s->read_zeroes) { >> - ret |= BDRV_BLOCK_ZERO; >> - } >> + ret |= s->read_zeroes ? BDRV_BLOCK_ZERO : BDRV_BLOCK_DATA; >> return ret; >> } >> >> diff --git a/qapi/block-core.json b/qapi/block-core.json >> index b1937780e1..7c95c9e36a 100644 >> --- a/qapi/block-core.json >> +++ b/qapi/block-core.json >> @@ -3293,8 +3293,9 @@ >> # requests. Default to zero which completes requests immediately. >> # (Since 2.4) >> # >> -# @read-zeroes: if true, reads from the device produce zeroes; if >> -# false, the buffer is left unchanged. >> +# @read-zeroes: if true, emulate a sparse image, and reads from the >> +# device produce zeroes; if false, emulate an allocated image but >> +# reads from the device leave the buffer unchanged. >> # (default: false; since: 4.1) >> # >> # Since: 2.9 > > Possibly dumb question: how is this doc change related to the code fix? > > Suggest to split the sentence for easier reading: > > # @read-zeroes: If true, emulate a sparse image, and reads from the > # device produce zeroes. If false, emulate an allocated image, > # but reads from the device leave the buffer unchanged. false is a security hazard, as secure-coding-practices.rst points out. I think it should be pointed out right here as well. Especially since "security hazard" is the default! I'd do it in a separate patch, but I'm a compulsive patch splitter.