From patchwork Fri May 11 19:19:46 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Luiz Capitulino X-Patchwork-Id: 158569 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 994DBB700C for ; Sat, 12 May 2012 05:20:02 +1000 (EST) Received: from localhost ([::1]:58849 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SSvNf-0005NW-Jr for incoming@patchwork.ozlabs.org; Fri, 11 May 2012 15:19:59 -0400 Received: from eggs.gnu.org ([208.118.235.92]:39640) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SSvNT-0005Dc-Lt for qemu-devel@nongnu.org; Fri, 11 May 2012 15:19:49 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1SSvNQ-0007Nf-4P for qemu-devel@nongnu.org; Fri, 11 May 2012 15:19:47 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51133) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SSvNP-0007MQ-S3 for qemu-devel@nongnu.org; Fri, 11 May 2012 15:19:44 -0400 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id q4BJJen8026778 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Fri, 11 May 2012 15:19:41 -0400 Received: from localhost (ovpn-116-25.ams2.redhat.com [10.36.116.25]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id q4BJJcag016793; Fri, 11 May 2012 15:19:39 -0400 From: Luiz Capitulino To: mdroth@linux.vnet.ibm.com Date: Fri, 11 May 2012 16:19:46 -0300 Message-Id: <1336763987-10920-2-git-send-email-lcapitulino@redhat.com> In-Reply-To: <1336763987-10920-1-git-send-email-lcapitulino@redhat.com> References: <1336763987-10920-1-git-send-email-lcapitulino@redhat.com> X-Scanned-By: MIMEDefang 2.68 on 10.5.11.22 X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 209.132.183.28 Cc: qemu-devel@nongnu.org Subject: [Qemu-devel] [PATCH 1/2] qemu-ga: guest-suspend: make the API synchronous X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Currently, qemu-ga has a SIGCHLD handler that automatically reaps terminated children processes. The idea is to avoid having qemu-ga commands blocked waiting for children to terminate. That approach has two problems: 1. qemu-ga is unable to detect errors in the child, meaning that qemu-ga returns success even if the child fails to perform its task 2. if a command does depend on the child exit status, the command has to play tricks to bypass the automatic reaper Case 2 impacts the guest-suspend-* API, because it has to execute an external program to check for suspend support. Today, to bypass the automatic reaper, suspend code has to double fork and pass exit status information through a pipe. Besides being complex, this is prone to race condition bugs. Indeed, the current code does have such bugs. Making the guest-suspend-* API synchronous (ie. by dropping the SIGCHLD handler and calling waitpid() from commands) is a much simpler approach, which fixes current race conditions bugs and enables commands to detect errors in the child. This commit does just that. There's a side effect though, guest-shutdown will generate zombies if shutting down fails. This will be fixed by the next commit. Signed-off-by: Luiz Capitulino --- qemu-ga.c | 17 +------ qga/commands-posix.c | 124 ++++++++++++++++++++------------------------------ 2 files changed, 51 insertions(+), 90 deletions(-) diff --git a/qemu-ga.c b/qemu-ga.c index 822f527..c0ca8b2 100644 --- a/qemu-ga.c +++ b/qemu-ga.c @@ -104,16 +104,9 @@ static void quit_handler(int sig) } #ifndef _WIN32 -/* reap _all_ terminated children */ -static void child_handler(int sig) -{ - int status; - while (waitpid(-1, &status, WNOHANG) > 0) /* NOTHING */; -} - static gboolean register_signal_handlers(void) { - struct sigaction sigact, sigact_chld; + struct sigaction sigact; int ret; memset(&sigact, 0, sizeof(struct sigaction)); @@ -130,14 +123,6 @@ static gboolean register_signal_handlers(void) return false; } - memset(&sigact_chld, 0, sizeof(struct sigaction)); - sigact_chld.sa_handler = child_handler; - sigact_chld.sa_flags = SA_NOCLDSTOP; - ret = sigaction(SIGCHLD, &sigact_chld, NULL); - if (ret == -1) { - g_error("error configuring signal handler: %s", strerror(errno)); - } - return true; } diff --git a/qga/commands-posix.c b/qga/commands-posix.c index 2ce9b82..a61f9e0 100644 --- a/qga/commands-posix.c +++ b/qga/commands-posix.c @@ -512,117 +512,86 @@ static void guest_fsfreeze_cleanup(void) #define SUSPEND_SUPPORTED 0 #define SUSPEND_NOT_SUPPORTED 1 -/** - * This function forks twice and the information about the mode support - * status is passed to the qemu-ga process via a pipe. - * - * This approach allows us to keep the way we reap terminated children - * in qemu-ga quite simple. - */ static void bios_supports_mode(const char *pmutils_bin, const char *pmutils_arg, const char *sysfile_str, Error **err) { - pid_t pid; - ssize_t ret; char *pmutils_path; - int status, pipefds[2]; - - if (pipe(pipefds) < 0) { - error_set(err, QERR_UNDEFINED_ERROR); - return; - } + pid_t pid, rpid; + int status; pmutils_path = g_find_program_in_path(pmutils_bin); pid = fork(); if (!pid) { - struct sigaction act; - - memset(&act, 0, sizeof(act)); - act.sa_handler = SIG_DFL; - sigaction(SIGCHLD, &act, NULL); + char buf[32]; /* hopefully big enough */ + ssize_t ret; + int fd; setsid(); - close(pipefds[0]); reopen_fd_to_null(0); reopen_fd_to_null(1); reopen_fd_to_null(2); - pid = fork(); - if (!pid) { - int fd; - char buf[32]; /* hopefully big enough */ - - if (pmutils_path) { - execle(pmutils_path, pmutils_bin, pmutils_arg, NULL, environ); - } - - /* - * If we get here either pm-utils is not installed or execle() has - * failed. Let's try the manual method if the caller wants it. - */ - - if (!sysfile_str) { - _exit(SUSPEND_NOT_SUPPORTED); - } - - fd = open(LINUX_SYS_STATE_FILE, O_RDONLY); - if (fd < 0) { - _exit(SUSPEND_NOT_SUPPORTED); - } + if (pmutils_path) { + execle(pmutils_path, pmutils_bin, pmutils_arg, NULL, environ); + } - ret = read(fd, buf, sizeof(buf)-1); - if (ret <= 0) { - _exit(SUSPEND_NOT_SUPPORTED); - } - buf[ret] = '\0'; + /* + * If we get here either pm-utils is not installed or execle() has + * failed. Let's try the manual method if the caller wants it. + */ - if (strstr(buf, sysfile_str)) { - _exit(SUSPEND_SUPPORTED); - } + if (!sysfile_str) { + _exit(SUSPEND_NOT_SUPPORTED); + } + fd = open(LINUX_SYS_STATE_FILE, O_RDONLY); + if (fd < 0) { _exit(SUSPEND_NOT_SUPPORTED); } - if (pid > 0) { - wait(&status); - } else { - status = SUSPEND_NOT_SUPPORTED; + ret = read(fd, buf, sizeof(buf)-1); + if (ret <= 0) { + _exit(SUSPEND_NOT_SUPPORTED); } + buf[ret] = '\0'; - ret = write(pipefds[1], &status, sizeof(status)); - if (ret != sizeof(status)) { - _exit(EXIT_FAILURE); + if (strstr(buf, sysfile_str)) { + _exit(SUSPEND_SUPPORTED); } - _exit(EXIT_SUCCESS); + _exit(SUSPEND_NOT_SUPPORTED); } - close(pipefds[1]); g_free(pmutils_path); if (pid < 0) { - error_set(err, QERR_UNDEFINED_ERROR); - goto out; - } - - ret = read(pipefds[0], &status, sizeof(status)); - if (ret == sizeof(status) && WIFEXITED(status) && - WEXITSTATUS(status) == SUSPEND_SUPPORTED) { - goto out; + goto undef_err; + } + + rpid = waitpid(pid, &status, 0); + if (rpid == pid && WIFEXITED(status)) { + switch (WEXITSTATUS(status)) { + case SUSPEND_SUPPORTED: + return; + case SUSPEND_NOT_SUPPORTED: + error_set(err, QERR_UNSUPPORTED); + return; + default: + goto undef_err; + } } - error_set(err, QERR_UNSUPPORTED); - -out: - close(pipefds[0]); +undef_err: + error_set(err, QERR_UNDEFINED_ERROR); } static void guest_suspend(const char *pmutils_bin, const char *sysfile_str, Error **err) { - pid_t pid; char *pmutils_path; + pid_t rpid, pid; + int status; pmutils_path = g_find_program_in_path(pmutils_bin); @@ -664,9 +633,16 @@ static void guest_suspend(const char *pmutils_bin, const char *sysfile_str, g_free(pmutils_path); if (pid < 0) { - error_set(err, QERR_UNDEFINED_ERROR); + goto exit_err; + } + + rpid = waitpid(pid, &status, 0); + if (rpid == pid && WIFEXITED(status) && !WEXITSTATUS(status)) { return; } + +exit_err: + error_set(err, QERR_UNDEFINED_ERROR); } void qmp_guest_suspend_disk(Error **err)