{"id":26510,"url":"https://patchwork.libcamera.org/api/patches/26510/?format=json","web_url":"https://patchwork.libcamera.org/patch/26510/","project":{"id":1,"url":"https://patchwork.libcamera.org/api/projects/1/?format=json","name":"libcamera","link_name":"libcamera","list_id":"libcamera_core","list_email":"libcamera-devel@lists.libcamera.org","web_url":"","scm_url":"","webscm_url":""},"msgid":"<20260408115630.12456-4-johannes.goede@oss.qualcomm.com>","date":"2026-04-08T11:56:30","name":"[3/3] libcamera: v4l2_device: add lock() and unlock() methods","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"0fd248ba42b917bc321531b299cbefa29f4b57d8","submitter":{"id":242,"url":"https://patchwork.libcamera.org/api/people/242/?format=json","name":"Hans de Goede","email":"johannes.goede@oss.qualcomm.com"},"delegate":null,"mbox":"https://patchwork.libcamera.org/patch/26510/mbox/","series":[{"id":5877,"url":"https://patchwork.libcamera.org/api/series/5877/?format=json","web_url":"https://patchwork.libcamera.org/project/libcamera/list/?series=5877","date":"2026-04-08T11:56:27","name":"libcamera: Finer grained MediaDevice locking","version":1,"mbox":"https://patchwork.libcamera.org/series/5877/mbox/"}],"comments":"https://patchwork.libcamera.org/api/patches/26510/comments/","check":"pending","checks":"https://patchwork.libcamera.org/api/patches/26510/checks/","tags":{},"headers":{"Return-Path":"","X-Original-To":"parsemail@patchwork.libcamera.org","Delivered-To":"parsemail@patchwork.libcamera.org","Received":["from lancelot.ideasonboard.com (lancelot.ideasonboard.com\n\t[92.243.16.209])\n\tby patchwork.libcamera.org (Postfix) with ESMTPS id 8B65EC32BB\n\tfor ;\n\tWed, 8 Apr 2026 11:56:41 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id 436D762E13;\n\tWed, 8 Apr 2026 13:56:41 +0200 (CEST)","from mx0b-0031df01.pphosted.com (mx0b-0031df01.pphosted.com\n\t[205.220.180.131])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 189C462E34\n\tfor ;\n\tWed, 8 Apr 2026 13:56:38 +0200 (CEST)","from pps.filterd (m0279872.ppops.net [127.0.0.1])\n\tby mx0a-0031df01.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id\n\t638BOaDe1619593 for ;\n\tWed, 8 Apr 2026 11:56:38 GMT","from mail-qt1-f197.google.com (mail-qt1-f197.google.com\n\t[209.85.160.197])\n\tby mx0a-0031df01.pphosted.com (PPS) with ESMTPS id 4ddacrjnvq-1\n\t(version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NOT)\n\tfor ;\n\tWed, 08 Apr 2026 11:56:37 +0000 (GMT)","by mail-qt1-f197.google.com with SMTP id\n\td75a77b69052e-50d831e8083so76716411cf.3\n\tfor ;\n\tWed, 08 Apr 2026 04:56:37 -0700 (PDT)","from t14s\n\t(2001-1c00-0c32-7800-07d4-cca3-ec08-7ac7.cable.dynamic.v6.ziggo.nl.\n\t[2001:1c00:c32:7800:7d4:cca3:ec08:7ac7])\n\tby smtp.gmail.com with ESMTPSA id\n\ta640c23a62f3a-b9c3c97219dsm632410766b.5.2026.04.08.04.56.35\n\t(version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256);\n\tWed, 08 Apr 2026 04:56:35 -0700 (PDT)"],"Authentication-Results":"lancelot.ideasonboard.com; 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To allow the different instances to coexist, system resources like\n+ * v4l2 devices must be accessible for enumerating the cameras they provide at\n+ * all times, while still allowing an instance to lock a resource while it\n+ * prepares to actively use a camera from the resource.\n+ *\n+ * \\return True if the device could be locked, false otherwise\n+ * \\sa unlock()\n+ */\n+bool V4L2Device::lock()\n+{\n+\tif (!fd_.isValid())\n+\t\treturn false;\n+\n+\tif (lockf(fd_.get(), F_TLOCK, 0))\n+\t\treturn false;\n+\n+\treturn true;\n+}\n+\n+/**\n+ * \\brief Unlock the device and free it for use for libcamera instances\n+ *\n+ * \\sa lock()\n+ */\n+void V4L2Device::unlock()\n+{\n+\tif (!fd_.isValid())\n+\t\treturn;\n+\n+\tstd::ignore = lockf(fd_.get(), F_ULOCK, 0);\n+}\n+\n /**\n * \\fn V4L2Device::isOpen()\n * \\brief Check if the V4L2 device node is open\n","prefixes":["3/3"]}