{"id":24144,"url":"https://patchwork.libcamera.org/api/1.1/patches/24144/?format=json","web_url":"https://patchwork.libcamera.org/patch/24144/","project":{"id":1,"url":"https://patchwork.libcamera.org/api/1.1/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":"<20250815141237.2235085-1-barnabas.pocze@ideasonboard.com>","date":"2025-08-15T14:12:37","name":"[RFC,v1] apps: cam: Use signalfd","commit_ref":null,"pull_url":null,"state":"superseded","archived":false,"hash":"b37c0ca36519f41589376772f5a25f2177349895","submitter":{"id":216,"url":"https://patchwork.libcamera.org/api/1.1/people/216/?format=json","name":"Barnabás Pőcze","email":"barnabas.pocze@ideasonboard.com"},"delegate":null,"mbox":"https://patchwork.libcamera.org/patch/24144/mbox/","series":[{"id":5386,"url":"https://patchwork.libcamera.org/api/1.1/series/5386/?format=json","web_url":"https://patchwork.libcamera.org/project/libcamera/list/?series=5386","date":"2025-08-15T14:12:37","name":"[RFC,v1] apps: cam: Use signalfd","version":1,"mbox":"https://patchwork.libcamera.org/series/5386/mbox/"}],"comments":"https://patchwork.libcamera.org/api/patches/24144/comments/","check":"pending","checks":"https://patchwork.libcamera.org/api/patches/24144/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 8E508BEFBE\n\tfor ;\n\tFri, 15 Aug 2025 14:12:43 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id C94386924E;\n\tFri, 15 Aug 2025 16:12:42 +0200 (CEST)","from perceval.ideasonboard.com (perceval.ideasonboard.com\n\t[213.167.242.64])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 1414D61443\n\tfor ;\n\tFri, 15 Aug 2025 16:12:41 +0200 (CEST)","from pb-laptop.local (185.221.141.188.nat.pool.zt.hu\n\t[185.221.141.188])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id F1B8A56D\n\tfor ;\n\tFri, 15 Aug 2025 16:11:45 +0200 (CEST)"],"Authentication-Results":"lancelot.ideasonboard.com; dkim=pass (1024-bit key;\n\tunprotected) header.d=ideasonboard.com header.i=@ideasonboard.com\n\theader.b=\"jPGbHIvZ\"; dkim-atps=neutral","DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1755267106;\n\tbh=iSEEvTzxH/kZ6+Qooc2+hH3qsUAIFaVNhsZIqs4+2mI=;\n\th=From:To:Subject:Date:From;\n\tb=jPGbHIvZHj8sjVr6364OJ/n4l2Z4RBNykTGYQ1QAhGzuYaQu2+jCQqEmIP1OdOufO\n\tfn+9P+dPTbsxiyaHgKMuV6/wPa3shbUzP+W4hXfYeGJURIRVWMsWFIQWvl3XNUkHVU\n\t6OrarDbUetmx/fC1zfzZU1Vn2tbr9AfgXN0OYi8Q=","From":"=?utf-8?q?Barnab=C3=A1s_P=C5=91cze?= ","To":"libcamera-devel@lists.libcamera.org","Subject":"[RFC PATCH v1] apps: cam: Use signalfd","Date":"Fri, 15 Aug 2025 16:12:37 +0200","Message-ID":"<20250815141237.2235085-1-barnabas.pocze@ideasonboard.com>","X-Mailer":"git-send-email 2.50.1","MIME-Version":"1.0","Content-Type":"text/plain; charset=UTF-8","Content-Transfer-Encoding":"8bit","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","Errors-To":"libcamera-devel-bounces@lists.libcamera.org","Sender":"\"libcamera-devel\" "},"content":"Use a signalfd to detect `SIGINT` instead of registering a signal handler in\norder to remove the `CamApp` singleton. This is better than using a normal\nsignal handler: a signal can arrive after the `CamApp` object has been destroyed,\nleading to a use-after-free. Modifying the `CamApp::app_` in the destructor is\nnot a good alternative because that would not be async signal safe (unless it\nis made atomic).\n\nSigned-off-by: Barnabás Pőcze \n---\n src/apps/cam/main.cpp | 66 +++++++++++++++++++------------------------\n 1 file changed, 29 insertions(+), 37 deletions(-)\n\n--\n2.50.1","diff":"diff --git a/src/apps/cam/main.cpp b/src/apps/cam/main.cpp\nindex fa266eca6..cbc85b59f 100644\n--- a/src/apps/cam/main.cpp\n+++ b/src/apps/cam/main.cpp\n@@ -13,6 +13,8 @@\n #include \n #include \n\n+#include \n+\n #include \n #include \n\n@@ -27,15 +29,12 @@ using namespace libcamera;\n class CamApp\n {\n public:\n-\tCamApp();\n-\n-\tstatic CamApp *instance();\n+\tCamApp(EventLoop &loop);\n\n \tint init(int argc, char **argv);\n \tvoid cleanup();\n\n \tint exec();\n-\tvoid quit();\n\n private:\n \tvoid cameraAdded(std::shared_ptr cam);\n@@ -46,26 +45,17 @@ private:\n\n \tstatic std::string cameraName(const Camera *camera);\n\n-\tstatic CamApp *app_;\n \tOptionsParser::Options options_;\n\n \tstd::unique_ptr cm_;\n\n \tstd::atomic_uint loopUsers_;\n-\tEventLoop loop_;\n+\tEventLoop *loop_ = nullptr;\n };\n\n-CamApp *CamApp::app_ = nullptr;\n-\n-CamApp::CamApp()\n-\t: loopUsers_(0)\n-{\n-\tCamApp::app_ = this;\n-}\n-\n-CamApp *CamApp::instance()\n+CamApp::CamApp(EventLoop &loop)\n+\t: loopUsers_(0), loop_(&loop)\n {\n-\treturn CamApp::app_;\n }\n\n int CamApp::init(int argc, char **argv)\n@@ -103,11 +93,6 @@ int CamApp::exec()\n \treturn ret;\n }\n\n-void CamApp::quit()\n-{\n-\tloop_.exit();\n-}\n-\n int CamApp::parseOptions(int argc, char *argv[])\n {\n \tStreamKeyValueParser streamKeyValue;\n@@ -205,7 +190,7 @@ void CamApp::cameraRemoved(std::shared_ptr cam)\n void CamApp::captureDone()\n {\n \tif (--loopUsers_ == 0)\n-\t\tEventLoop::instance()->exit(0);\n+\t\tloop_->exit(0);\n }\n\n int CamApp::run()\n@@ -290,7 +275,7 @@ int CamApp::run()\n \t}\n\n \tif (loopUsers_)\n-\t\tloop_.exec();\n+\t\tloop_->exec();\n\n \t/* 6. Stop capture. */\n \tfor (const auto &session : sessions) {\n@@ -345,29 +330,36 @@ std::string CamApp::cameraName(const Camera *camera)\n \treturn name;\n }\n\n-namespace {\n-\n-void signalHandler([[maybe_unused]] int signal)\n+int main(int argc, char **argv)\n {\n-\tstd::cout << \"Exiting\" << std::endl;\n-\tCamApp::instance()->quit();\n-}\n+\tauto sigfd = [] {\n+\t\tsigset_t ss;\n\n-} /* namespace */\n+\t\tsigemptyset(&ss);\n+\t\tsigaddset(&ss, SIGINT);\n+\t\tsigprocmask(SIG_BLOCK, &ss, nullptr);\n\n-int main(int argc, char **argv)\n-{\n-\tCamApp app;\n+\t\treturn UniqueFD(signalfd(-1, &ss, SFD_CLOEXEC | SFD_NONBLOCK));\n+\t}();\n+\tif (!sigfd.isValid())\n+\t\treturn EXIT_FAILURE;\n+\n+\tEventLoop loop;\n+\tCamApp app(loop);\n \tint ret;\n\n+\tloop.addFdEvent(sigfd.get(), EventLoop::Read, [&] {\n+\t\tsignalfd_siginfo si;\n+\t\tstd::ignore = read(sigfd.get(), &si, sizeof(si));\n+\n+\t\tstd::cout << \"Exiting\" << std::endl;\n+\t\tloop.exit(0);\n+\t});\n+\n \tret = app.init(argc, argv);\n \tif (ret)\n \t\treturn ret == -EINTR ? 0 : EXIT_FAILURE;\n\n-\tstruct sigaction sa = {};\n-\tsa.sa_handler = &signalHandler;\n-\tsigaction(SIGINT, &sa, nullptr);\n-\n \tif (app.exec())\n \t\treturn EXIT_FAILURE;\n\n","prefixes":["RFC","v1"]}