[{"id":1588,"web_url":"https://patchwork.libcamera.org/comment/1588/","msgid":"<20190511130935.GG4946@pendragon.ideasonboard.com>","date":"2019-05-11T13:09:35","subject":"Re: [libcamera-devel] [PATCH v3 08/11] libcamera: media_device: Add\n\tfunctions to lock device for other processes","submitter":{"id":2,"url":"https://patchwork.libcamera.org/api/people/2/","name":"Laurent Pinchart","email":"laurent.pinchart@ideasonboard.com"},"content":"Hi Niklas,\n\nThank you for the patch.\n\nOn Sat, May 11, 2019 at 11:19:04AM +0200, Niklas Söderlund wrote:\n> Add lock() and unlock() which are backed by lockf() and allows an\n\ns/allows/allow/\n\n> instance of libcamera to claim exclusive access to a media device.\n> These functions are the base of allowing multiple user of libcamera to\n> coexist in the system without stepping on each others toes.\n\ns/others/other's/\n\n> \n> Signed-off-by: Niklas Söderlund \n> ---\n> src/libcamera/include/media_device.h | 4 ++\n> src/libcamera/media_device.cpp | 58 +++++++++++++++++++++++++++-\n> 2 files changed, 61 insertions(+), 1 deletion(-)\n> \n> diff --git a/src/libcamera/include/media_device.h b/src/libcamera/include/media_device.h\n> index e513a2fee1b91a1b..7b88e2875d59dfc3 100644\n> --- a/src/libcamera/include/media_device.h\n> +++ b/src/libcamera/include/media_device.h\n> @@ -30,6 +30,9 @@ public:\n> \tvoid release();\n> \tbool busy() const { return acquired_; }\n> \n> +\tbool lock();\n> +\tvoid unlock();\n> +\n> \tint populate();\n> \tbool valid() const { return valid_; }\n> \n> @@ -58,6 +61,7 @@ private:\n> \tint fd_;\n> \tbool valid_;\n> \tbool acquired_;\n> +\tbool lockOwner_;\n> \n> \tint open();\n> \tvoid close();\n> diff --git a/src/libcamera/media_device.cpp b/src/libcamera/media_device.cpp\n> index 62c59e7e8fc0299f..874ecc06e4bd9c94 100644\n> --- a/src/libcamera/media_device.cpp\n> +++ b/src/libcamera/media_device.cpp\n> @@ -63,7 +63,8 @@ LOG_DEFINE_CATEGORY(MediaDevice)\n> * populate() before the media graph can be queried.\n> */\n> MediaDevice::MediaDevice(const std::string &deviceNode)\n> -\t: deviceNode_(deviceNode), fd_(-1), valid_(false), acquired_(false)\n> +\t: deviceNode_(deviceNode), fd_(-1), valid_(false), acquired_(false),\n> +\t lockOwner_(false)\n> {\n> }\n> \n> @@ -118,6 +119,61 @@ void MediaDevice::release()\n> \tacquired_ = false;\n> }\n> \n> +/**\n> + * \\brief Lock the device for use by other instances of libcamera\n\nThis sounds a bit weird to me. Maybe \"Lock the device from being used by\nother instances of libcamera\" ? Feedback from a native speaker would be\nappreciated here (and for the unlock() method below). Apart from this,\n\nReviewed-by: Laurent Pinchart \n\n> + *\n> + * Multiple instances of libcamera might be running on the same system, at the\n> + * same time. To allow the different instances to coexist, system resources in\n> + * the form of media devices must be accessible for enumerating the cameras\n> + * they provide at all times, while still allowing an instance to lock a\n> + * resource while it prepares to actively use a camera from the resource.\n> + *\n> + * This method shall not be called from a pipeline handler implementation\n> + * directly, as the base PipelineHandler implementation handles this on the\n> + * behalf of the specified implementation.\n> + *\n> + * \\return True if the device could be locked, false otherwise\n> + * \\sa unlock()\n> + */\n> +bool MediaDevice::lock()\n> +{\n> +\tif (fd_ == -1)\n> +\t\treturn false;\n> +\n> +\t/* Do not allow nested locking in the same libcamera instance. */\n> +\tif (lockOwner_)\n> +\t\treturn false;\n> +\n> +\tif (lockf(fd_, F_TLOCK, 0))\n> +\t\treturn false;\n> +\n> +\tlockOwner_ = true;\n> +\n> +\treturn true;\n> +}\n> +\n> +/**\n> + * \\brief Unlock the device and free it for use for libcamera instances\n> + *\n> + * This method shall not be called from a pipeline handler implementation\n> + * directly, as the base PipelineHandler implementation handles this on the\n> + * behalf of the specified implementation.\n> + *\n> + * \\sa lock()\n> + */\n> +void MediaDevice::unlock()\n> +{\n> +\tif (fd_ == -1)\n> +\t\treturn;\n> +\n> +\tif (!lockOwner_)\n> +\t\treturn;\n> +\n> +\tlockOwner_ = false;\n> +\n> +\tlockf(fd_, F_ULOCK, 0);\n> +}\n> +\n> /**\n> * \\fn MediaDevice::busy()\n> * \\brief Check if a device is in use","headers":{"Return-Path":"","Received":["from perceval.ideasonboard.com (perceval.ideasonboard.com\n\t[IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id EE2A060E4F\n\tfor ;\n\tSat, 11 May 2019 15:09:59 +0200 (CEST)","from pendragon.ideasonboard.com\n\t(dfj612yhrgyx302h3jwwy-3.rev.dnainternet.fi\n\t[IPv6:2001:14ba:21f5:5b00:ce28:277f:58d7:3ca4])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id 6607CD5;\n\tSat, 11 May 2019 15:09:59 +0200 (CEST)"],"DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1557580199;\n\tbh=KRNOnze35LL9But8UUlMuctSj2ux1yled3/74owGaWQ=;\n\th=Date:From:To:Cc:Subject:References:In-Reply-To:From;\n\tb=gEk8Tre7jUqF2WXMCCEXki79nlmf4xO67UgJF8HQpq348Wpghe3KXL/YCxVXeIzwY\n\tVT8RhKquwNMR73x4rAZp4xA0ZicAa53JTHBGa6hJLPaNhjHnD29Ccc0cUMrm7D6GQP\n\tXfrb3FvuEkBC/CyZrjdvnFXQiHY/jBqNLHTTtA3E=","Date":"Sat, 11 May 2019 16:09:35 +0300","From":"Laurent Pinchart ","To":"Niklas =?utf-8?q?S=C3=B6derlund?= ","Cc":"libcamera-devel@lists.libcamera.org","Message-ID":"<20190511130935.GG4946@pendragon.ideasonboard.com>","References":"<20190511091907.10050-1-niklas.soderlund@ragnatech.se>\n\t<20190511091907.10050-9-niklas.soderlund@ragnatech.se>","MIME-Version":"1.0","Content-Type":"text/plain; charset=utf-8","Content-Disposition":"inline","Content-Transfer-Encoding":"8bit","In-Reply-To":"<20190511091907.10050-9-niklas.soderlund@ragnatech.se>","User-Agent":"Mutt/1.10.1 (2018-07-13)","Subject":"Re: [libcamera-devel] [PATCH v3 08/11] libcamera: media_device: Add\n\tfunctions to lock device for other processes","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.23","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","X-List-Received-Date":"Sat, 11 May 2019 13:10:00 -0000"}}]