From patchwork Wed Sep 6 12:05:02 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Hildenbrand X-Patchwork-Id: 13375627 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 48BC4EB8FAF for ; Wed, 6 Sep 2023 12:07:35 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qdrIe-0004lW-SW; Wed, 06 Sep 2023 08:06:24 -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 1qdrI5-0003u6-MX for qemu-devel@nongnu.org; Wed, 06 Sep 2023 08:05:52 -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 1qdrI2-0006oE-Q3 for qemu-devel@nongnu.org; Wed, 06 Sep 2023 08:05:49 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1694001944; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=mbNPx7DuHzIPzDXZqlQOvXnetMxZigkWuSBGkgASAno=; b=QjQwOwUDYpTLuuzxDRaYGtAkCD1pAifR5M7HxWCTZxMPy0gVNTPuEng1aUqYQaE/5dIZc1 zKwLl4oH8DE/8WJHva+M2zvj6weLZfXky1YM45meKAcomlu48xyZd8ILIW7H9Rf0wg9dD6 lT6mdpfCTJMmXbeQ3bBYUQipp73DrjY= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-688-gspBnm1ZO6Kn5VSqVZdE2g-1; Wed, 06 Sep 2023 08:05:43 -0400 X-MC-Unique: gspBnm1ZO6Kn5VSqVZdE2g-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 8C2478AA801; Wed, 6 Sep 2023 12:05:42 +0000 (UTC) Received: from t14s.fritz.box (unknown [10.39.192.60]) by smtp.corp.redhat.com (Postfix) with ESMTP id A01BD493110; Wed, 6 Sep 2023 12:05:39 +0000 (UTC) From: David Hildenbrand To: qemu-devel@nongnu.org Cc: David Hildenbrand , Paolo Bonzini , Peter Xu , Igor Mammedov , Thiner Logoer , =?utf-8?q?Philippe_Mathieu-Daud?= =?utf-8?q?=C3=A9?= , =?utf-8?q?Daniel_P_=2E_Berrang?= =?utf-8?q?=C3=A9?= , Stefan Hajnoczi , Elena Ufimtseva , Jagannathan Raman , "Michael S. Tsirkin" , Ani Sinha , Xiao Guangrong , Daniel Henrique Barboza , Greg Kurz , Eric Blake , Markus Armbruster , Eduardo Habkost Subject: [PATCH v4 10/11] softmmu/physmem: Hint that "readonly=on, rom=off" exists when opening file R/W for private mapping fails Date: Wed, 6 Sep 2023 14:05:02 +0200 Message-ID: <20230906120503.359863-11-david@redhat.com> In-Reply-To: <20230906120503.359863-1-david@redhat.com> References: <20230906120503.359863-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 Received-SPF: pass client-ip=170.10.133.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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 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 It's easy to miss that memory-backend-file with "share=off" (default) will always try opening the file R/W as default, and fail if we don't have write permissions to the file. In that case, the user has to explicit specify "readonly=on,rom=off" to get usable RAM, for example, for VM templating. Let's hint that '-object memory-backend-file,readonly=on,rom=off,...' exists to consume R/O files in a private mapping to create writable RAM, but only if we have permissions to open the file read-only. Suggested-by: ThinerLogoer Signed-off-by: David Hildenbrand --- softmmu/physmem.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/softmmu/physmem.c b/softmmu/physmem.c index f1cd3ec28a..4f6ca653b3 100644 --- a/softmmu/physmem.c +++ b/softmmu/physmem.c @@ -1969,6 +1969,25 @@ RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr, if (fd < 0) { error_setg_errno(errp, -fd, "can't open backing store %s for guest RAM", mem_path); + if (!(ram_flags & RAM_READONLY_FD) && !(ram_flags & RAM_SHARED) && + fd == -EACCES) { + /* + * If we can open the file R/O (note: will never create a new file) + * and we are dealing with a private mapping, there are still ways + * to consume such files and get RAM instead of ROM. + */ + fd = file_ram_open(mem_path, memory_region_name(mr), true, + &created); + if (fd < 0) { + return NULL; + } + assert(!created); + close(fd); + error_append_hint(errp, "Consider opening the backing store" + " read-only but still creating writable RAM using" + " '-object memory-backend-file,readonly=on,rom=off...'" + " (see \"VM templating\" documentation)\n"); + } return NULL; }