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=-15.1 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,USER_AGENT_SANE_1 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 AF664C433E0 for ; Wed, 17 Mar 2021 16:47:21 +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 2DF6264F3E for ; Wed, 17 Mar 2021 16:47:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2DF6264F3E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:33090 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lMZKJ-0005Jd-Oy for qemu-devel@archiver.kernel.org; Wed, 17 Mar 2021 12:47:19 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:59370) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lMYn4-0006yO-GP for qemu-devel@nongnu.org; Wed, 17 Mar 2021 12:13:00 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:40737) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lMYn1-0003v5-7O for qemu-devel@nongnu.org; Wed, 17 Mar 2021 12:12:58 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615997573; h=from:from:reply-to: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=hpZzmUCIaILTarUnrFjtxu6RGrHKUn/ZIOmdH5r9rPU=; b=AskYFkizJWE2cKEzSLrDvRPWn0/M6iUorftz858HqUA5Dxc+LYnclKAkFKxYLsDNF9fHS7 hM0c9yRY1YPsExT8RZjm7gvNfiBK+3or1HrZ1/8zElgmAR0jEnm3W8kMirH9eeNCz3pp/U Ei0Q/SCB6/r+4qCoYjmaWhZ97sbPPEs= 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-571-Yg9mkTXBN0elc9N-vaL0Lw-1; Wed, 17 Mar 2021 12:12:48 -0400 X-MC-Unique: Yg9mkTXBN0elc9N-vaL0Lw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id EF7B2A40C1; Wed, 17 Mar 2021 16:12:46 +0000 (UTC) Received: from redhat.com (ovpn-113-247.ams2.redhat.com [10.36.113.247]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 892FB5C1CF; Wed, 17 Mar 2021 16:12:45 +0000 (UTC) Date: Wed, 17 Mar 2021 16:12:42 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Kevin Wolf Subject: Re: [RFC PATCH] curl: Allow reading after EOF Message-ID: References: <20210317151734.41656-1-kwolf@redhat.com> MIME-Version: 1.0 In-Reply-To: <20210317151734.41656-1-kwolf@redhat.com> User-Agent: Mutt/2.0.5 (2021-01-21) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.251, 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_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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: afrosi@redhat.com, qemu-devel@nongnu.org, qemu-block@nongnu.org, mreitz@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Mar 17, 2021 at 04:17:34PM +0100, Kevin Wolf wrote: > This makes the curl driver more consistent with file-posix in that it > doesn't return errors any more for reading after the end of the remote > file. Instead, zeros are returned for these areas. > > This inconsistency was reported in: > https://bugzilla.redhat.com/show_bug.cgi?id=1935061 > > Note that the image used in this bug report has a corrupted snapshot > table, which means that the qcow2 driver tries to do a zero-length read > after EOF on its image file. > > The old behaviour of the curl driver can hardly be called a bug, but the > inconsistency turned out to be confusing. > > Reported-by: Alice Frosi > Signed-off-by: Kevin Wolf > --- > > It is not entirely clear to me if this is something we want to do. If we > do care about consistency between protocol drivers, something like this > should probably be done in block/io.c eventually - but that would > require converting bs->total_sectors to byte granularity first. > > Any opinions on what the most desirable semantics would be and whether > we should patch individual drivers until we can have a generic solution? What valid scenarios are there for wanting to read beyond the bounds of the protocol driver storage ? Why was file-posix allowing this so far ? If I've given file-posix a 10 GB plain file or device and something requests a read from the 11 GB offset, IMHO, that is a sign of serious error somewhere and possible impending doom. For writable storage, I would think that read + write should be symmetric, by which I mean if a read() at a particular offset succeeds, then I would also expect a write() at the same offset to succeed, and have its data later returned by a read(). We generally can't write at an offset beyond the storage (unless we are intending to auto-enlarge a plain file), so I think we shouldn't allow reads either. > > diff --git a/block/curl.c b/block/curl.c > index 50e741a0d7..a8d87a1813 100644 > --- a/block/curl.c > +++ b/block/curl.c > @@ -898,6 +898,7 @@ out: > static int coroutine_fn curl_co_preadv(BlockDriverState *bs, > uint64_t offset, uint64_t bytes, QEMUIOVector *qiov, int flags) > { > + BDRVCURLState *s = bs->opaque; > CURLAIOCB acb = { > .co = qemu_coroutine_self(), > .ret = -EINPROGRESS, > @@ -906,6 +907,15 @@ static int coroutine_fn curl_co_preadv(BlockDriverState *bs, > .bytes = bytes > }; > > + if (offset > s->len || bytes > s->len - offset) { > + uint64_t req_bytes = offset > s->len ? 0 : s->len - offset; > + qemu_iovec_memset(qiov, req_bytes, 0, bytes - req_bytes); > + bytes = req_bytes; > + } > + if (bytes == 0) { > + return 0; > + } > + > curl_setup_preadv(bs, &acb); > while (acb.ret == -EINPROGRESS) { > qemu_coroutine_yield(); > -- > 2.30.2 > > 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 :|