From patchwork Sat Dec 12 01:20:30 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dexuan Cui X-Patchwork-Id: 11969849 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=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 E8FEAC4361B for ; Sat, 12 Dec 2020 01:22:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 957CF2343E for ; Sat, 12 Dec 2020 01:22:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2406407AbgLLBVp (ORCPT ); Fri, 11 Dec 2020 20:21:45 -0500 Received: from mail-co1nam11on2113.outbound.protection.outlook.com ([40.107.220.113]:23392 "EHLO NAM11-CO1-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2405263AbgLLBVS (ORCPT ); Fri, 11 Dec 2020 20:21:18 -0500 ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=ZZSEyCggheYnmSMglFaougJVKsjs4AhHmUe7vbkWHo5rJHF9SRTen5Fs9P2+Uhua6C+rkuhW6Tp5sWcX3wYrnMYNEGFc+Lafg2Ue8blR/9d2mOgRTmg2TTY6vldFKlM2jTLd20TMiBRzck/VT7BD7zsKSLvuep3wL66p4xYmTmtKWUT7x0TlP3+U8/qA2BtJhp6hY1XXpYVThOSJcCDdvNcirGDNEeM/vFmu+nh6TfOMGOnkfQgYqex5FMBMNElXQYV21qebTDdXRrkIPUgDuh8tUZZJ4PwiEhLWQk8QOxs4ffMh/jahCxE4mXXKkDTbj2idVC6dq+5WZiTeEQwhUw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=0fqnKBCG7QBwhdU79CJLMXQqKjTazJFW1AVCZzVk0uw=; b=Zd4vEhgKdC9nPzGgiJs6Vaoji1hqDPNHZUV8Bz549yvva/wloHfP4nfrpZwPF/XLdl5Lo44OY2oMos/Nqhz09t8ZPSf05CZ5vGiab6bBgUD0O+ebRvAUEwuCh3IMmdzvxO1xwn7oD3mv/WiYQsy0vcBBoMcXz0+VvvrTLYZVkYhcS/AzSBJhVVwlrNl5oLyoXpxCVmZcIfZRXjDmpLvr2asW4DCiJShoHqEeWlP3h0pwqmUCjOSyghSQOHXWMF2JDgomCupi4ViymUHXTwNvg874wfcOpYY31CH9JrccxZ5FrepPV1VVoCJEihZfVF+TL6KLeKxlF8bFCuazKxAw8g== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=microsoft.com; dmarc=pass action=none header.from=microsoft.com; dkim=pass header.d=microsoft.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=selector2; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=0fqnKBCG7QBwhdU79CJLMXQqKjTazJFW1AVCZzVk0uw=; b=VXVNyAf4knmeOCS75yuTez7Gve/IDMJSdVcngvDItwe0iKOs7AAYvBnU6j5R7HalQwq6tspI0ouIdXA4NW196ru8sIqKvQSz2aEuzpL6VvavnbGyecsGjq0b2yWYY3KtFkyBcVVyCpiXNQZkOSY6QcmdnSgQ+yB+N6QB//Z9wmA= Received: from (2603:10b6:300:77::17) by MWHPR2101MB0874.namprd21.prod.outlook.com (2603:10b6:301:7e::39) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3654.2; Sat, 12 Dec 2020 01:20:30 +0000 Received: from MWHPR21MB0863.namprd21.prod.outlook.com ([fe80::9de4:6549:6890:b7ba]) by MWHPR21MB0863.namprd21.prod.outlook.com ([fe80::9de4:6549:6890:b7ba%5]) with mapi id 15.20.3654.018; Sat, 12 Dec 2020 01:20:30 +0000 From: Dexuan Cui To: "linux-acpi@vger.kernel.org" CC: "linux-kernel@vger.kernel.org" , "linux-hyperv@vger.kernel.org" , Michael Kelley Subject: How can a userspace program tell if the system supports the ACPI S4 state (Suspend-to-Disk)? Thread-Topic: How can a userspace program tell if the system supports the ACPI S4 state (Suspend-to-Disk)? 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In some scenarios IMO it can still be useful if the userspace is able to detect if the ACPI S4 state is supported or not, e.g. when a Linux guest runs on Hyper-V, Hyper-V uses the virtual ACPI S4 state as an indicator of the proper support of the tool stack on the host, i.e. the guest is discouraged from trying hibernation if the state is not supported. I know we can check the S4 state by 'dmesg': # dmesg |grep ACPI: | grep support [ 3.034134] ACPI: (supports S0 S4 S5) But this method is unreliable because the kernel msg buffer can be filled and overwritten. Is there any better method? If not, do you think if the below patch is appropriate? Thanks! Thanks, -- Dexuan diff --git a/kernel/power/main.c b/kernel/power/main.c index 0aefd6f57e0a..931a1526ea69 100644 --- a/kernel/power/main.c +++ b/kernel/power/main.c @@ -9,6 +9,7 @@ #include #include #include +#include #include #include #include @@ -600,8 +601,12 @@ static ssize_t state_show(struct kobject *kobj, struct kobj_attribute *attr, s += sprintf(s,"%s ", pm_states[i]); #endif - if (hibernation_available()) - s += sprintf(s, "disk "); + if (hibernation_available()) { + if (acpi_sleep_state_supported(ACPI_STATE_S4)) + s += sprintf(s, "disk+ "); + else + s += sprintf(s, "disk "); + } if (s != buf) /* convert the last space to a newline */ *(s-1) = '\n';