From patchwork Fri Apr 11 01:04:52 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eric Blake X-Patchwork-Id: 14047439 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 8523AC369AF for ; Fri, 11 Apr 2025 01:09:20 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1u32s7-0006KA-Sw; Thu, 10 Apr 2025 21:07:55 -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 1u32s2-0006Jm-PV for qemu-devel@nongnu.org; Thu, 10 Apr 2025 21:07:50 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1u32s0-0004I4-R7 for qemu-devel@nongnu.org; Thu, 10 Apr 2025 21:07:50 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1744333667; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=AZkyi0Zz5g4FNFrSOeCcuZwXAOyZvQwC0Ax4vbVu7IM=; b=LSyOves0LfTnqPH5hzgYsnnQwVR3evocpWw2cXyVVnw1YLqaDyvHT+eLsMBBYCIu974UxB JbzhcbAsFE+4PuZzI23YGbwUlgFmqIel3GAPlqWLCVrFtN0J9OVfJGsS/4V/gfuflbL0/1 o5IWF47CSNn+PvjsrFgTxe0mEj9lqJc= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-155--z2AMpp5PDeiowqW3XM5Zw-1; Thu, 10 Apr 2025 21:07:44 -0400 X-MC-Unique: -z2AMpp5PDeiowqW3XM5Zw-1 X-Mimecast-MFC-AGG-ID: -z2AMpp5PDeiowqW3XM5Zw_1744333663 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 83E5B1801A00; Fri, 11 Apr 2025 01:07:43 +0000 (UTC) Received: from green.redhat.com (unknown [10.2.16.21]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 90ED318009BC; Fri, 11 Apr 2025 01:07:42 +0000 (UTC) From: Eric Blake To: qemu-devel@nongnu.org Cc: Kevin Wolf , Hanna Reitz , qemu-block@nongnu.org (open list:raw) Subject: [PATCH 2/6] file-posix: Allow lseek at offset 0 when !want_zero Date: Thu, 10 Apr 2025 20:04:52 -0500 Message-ID: <20250411010732.358817-10-eblake@redhat.com> In-Reply-To: <20250411010732.358817-8-eblake@redhat.com> References: <20250411010732.358817-8-eblake@redhat.com> MIME-Version: 1.0 Content-type: text/plain X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Received-SPF: pass client-ip=170.10.129.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -26 X-Spam_score: -2.7 X-Spam_bar: -- X-Spam_report: (-2.7 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.593, 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_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_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 The 'want_zero' parameter to raw_co_block_status() was added so that we can avoid potentially time-consuming lseek(SEEK_DATA) calls throughout the file (working around poor filesystems that have O(n) rather than O(1) extent probing). But when it comes to learning if a file is completely sparse (for example, it was just created), always claiming that a file is all data without even checking offset 0 breaks what would otherwise be attempts at useful optimizations for a known-zero mirror destination. Note that this allows file-posix to report a file as completely zero if it was externally created (such as via 'truncate --size=$n file') as entirely sparse; however, it does NOT work for files created internally by blockdev-create. That's because blockdev-create intentionally does a sequence of truncate(0), truncate(size), allocate_first_block(), in order to make it possible for gluster on XFS to probe the sector size for direct I/O (which doesn't work if the first block is sparse). That will be addressed in a later patch. Signed-off-by: Eric Blake --- block/file-posix.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/block/file-posix.c b/block/file-posix.c index 56d1972d156..67e83528cf5 100644 --- a/block/file-posix.c +++ b/block/file-posix.c @@ -3217,7 +3217,14 @@ static int coroutine_fn raw_co_block_status(BlockDriverState *bs, return ret; } - if (!want_zero) { + /* + * If want_zero is clear, then the caller wants speed over + * accuracy, and the only place where SEEK_DATA should be + * attempted is at the start of the file to learn if the file has + * any data at all (anywhere else, just blindly claim the entire + * file is data). + */ + if (!want_zero && offset) { *pnum = bytes; *map = offset; *file = bs;