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[209.51.188.17]) by mx.google.com with ESMTPS id ada2fe7eead31-4b2bfb1ddb9si3658321137.222.2025.01.07.07.49.49 for (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Tue, 07 Jan 2025 07:49:49 -0800 (PST) Received-SPF: pass (google.com: domain of qemu-arm-bounces+alex.bennee=linaro.org@nongnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; Authentication-Results: mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=f1amtqeP; spf=pass (google.com: domain of qemu-arm-bounces+alex.bennee=linaro.org@nongnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom="qemu-arm-bounces+alex.bennee=linaro.org@nongnu.org"; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1tVBpl-0004ef-L1; Tue, 07 Jan 2025 10:49:33 -0500 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 1tVBpf-0004dx-C5 for qemu-arm@nongnu.org; Tue, 07 Jan 2025 10:49:27 -0500 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 1tVBpd-0006qu-O2 for qemu-arm@nongnu.org; Tue, 07 Jan 2025 10:49:27 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1736264964; 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=1WumwGpnFuIBztcl4qjZngxaSVLAmn1Sgu72KHgiURs=; b=f1amtqePMnwc3sGJcjCzraEDZWLmHvqlbymbFWWeeswailY7IJ6bucGwUl8MXwlOP0z3EC HQBnxBbi6pavS2qHq6OweV/9frhW1/5hNTSos/en0VNk1fwdIu+jmCPnNQdspM0s1HQ16g jbubqewvcueCP6P66XRGSlzMSX33KrE= Received: from mx-prod-mc-01.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-674-Lh7fb98aPGqSgSuuDzKFuQ-1; Tue, 07 Jan 2025 10:49:20 -0500 X-MC-Unique: Lh7fb98aPGqSgSuuDzKFuQ-1 X-Mimecast-MFC-AGG-ID: Lh7fb98aPGqSgSuuDzKFuQ Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (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-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 0193F1956089; Tue, 7 Jan 2025 15:49:18 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.64]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 65F391955F57; Tue, 7 Jan 2025 15:49:12 +0000 (UTC) Date: Tue, 7 Jan 2025 15:49:09 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Gerd Hoffmann Cc: qemu-devel@nongnu.org, graf@amazon.com, Paolo Bonzini , Michael Roth , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Thomas Huth , qemu-arm@nongnu.org, Eric Blake , Peter Maydell , Markus Armbruster , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau Subject: Re: [PATCH v2 13/21] hw/uefi: add var-service-json.c + qapi for NV vars. Message-ID: References: <20250107153353.1144978-1-kraxel@redhat.com> <20250107153353.1144978-14-kraxel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20250107153353.1144978-14-kraxel@redhat.com> User-Agent: Mutt/2.2.13 (2024-03-09) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.437, 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_H2=-0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-arm@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-arm-bounces+alex.bennee=linaro.org@nongnu.org Sender: qemu-arm-bounces+alex.bennee=linaro.org@nongnu.org X-TUID: TzOaq/ewtdmn On Tue, Jan 07, 2025 at 04:33:40PM +0100, Gerd Hoffmann wrote: > Define qapi schema for the uefi variable store state. > > Use it and the generated visitor helper functions to store persistent > (EFI_VARIABLE_NON_VOLATILE) variables in JSON format on disk. > > Signed-off-by: Gerd Hoffmann > --- > hw/uefi/var-service-json.c | 242 +++++++++++++++++++++++++++++++++++++ > qapi/meson.build | 1 + > qapi/qapi-schema.json | 1 + > qapi/uefi.json | 45 +++++++ > 4 files changed, 289 insertions(+) > create mode 100644 hw/uefi/var-service-json.c > create mode 100644 qapi/uefi.json > > +void uefi_vars_json_init(uefi_vars_state *uv, Error **errp) > +{ > + if (uv->jsonfile) { > + uv->jsonfd = qemu_create(uv->jsonfile, O_RDWR, 0666, errp); > + } > +} > + > +void uefi_vars_json_save(uefi_vars_state *uv) > +{ > + GString *gstr; > + int rc; > + > + if (uv->jsonfd == -1) { > + return; > + } > + > + gstr = uefi_vars_to_json(uv); > + > + lseek(uv->jsonfd, 0, SEEK_SET); > + rc = write(uv->jsonfd, gstr->str, gstr->len); > + if (rc != gstr->len) { > + warn_report("%s: write error", __func__); > + } > + rc = ftruncate(uv->jsonfd, gstr->len); > + if (rc != 0) { > + warn_report("%s: ftruncate error", __func__); > + } > + fsync(uv->jsonfd); Although the fsync helps, re-writing the file in-place is a ad idea for data integrity on host OS crash. Especially if the new data is shorter, we would easily end up with a file containing old and new data making it unparsable (assuming the parser doesn't ignore trailing data). I'd like to suggest the write to temp file + rename dance to get atomic replacement. The problem with that is that it hits the DAC/MAC security restrictions we put QEMU under :-( My next best idea is to re-arrange things thus: lseek(fd, 0) ftruncate(fd, 0) fsync(fd) write(fd, str) fsync(fd) so we should at least reduce the liklihood of getting a mix of old and new data - empty file is better than a mix of data. With 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 :|