lib/process: Add process helpers

We've grown-out of pb_run_cmd a little, as we have a number of different
process types:

   boot():
    - kexec: short-running process, run synchronously
    - boot hooks: short-running, run sync, need exit code & stdout

   network init:
    - interface configuration: short running, run sync
    - udhcp processes are long running, we may want completion, but
      doesn't block other actions

   downloads:
    - potentially long-running, block parse progress

   config nvram:
    - read: short running, can block, need stdout
    - write: short running, can block

We'd like to introduce proper asynchronous processes, to allow config &
boot-option downloads without blocking the discover server.

This change introduces a new type for processes, 'struct process'. These
structures are created with process_create, and run with
process_run_sync or process_run_async. The latter reports completion
through a callback member of struct process.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>

2 files changed, 513 insertions, 0 deletions

diff --git a/lib/process/process.c b/lib/process/process.c
new file mode 100644
index 0000000..e1a158b
--- /dev/null
+++ b/lib/process/process.c
@@ -0,0 +1,437 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include <assert.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/wait.h>
+
+#include <process/process.h>
+#include <talloc/talloc.h>
+#include <waiter/waiter.h>
+#include <log/log.h>
+
+struct procset {
+	struct waitset		*waitset;
+	struct list		async_list;
+	int			sigchld_pipe[2];
+	struct waiter		*sigchld_waiter;
+};
+
+/* Internal data type for process handling
+ *
+ * Allocation: these structures may have multiple references:
+ *  - from the original ctx pointer
+ *  - due to inclusion in async_list
+ *  - due to a currently-registered waiter
+ *
+ */
+struct process_info {
+#ifdef DEBUG
+	/* prevent talloc_free(process) from working */
+	int			__pad;
+#endif
+	struct process		process;
+	struct list_item	async_list;
+	int			stdout_buf_len;
+	struct waiter		*stdout_waiter;
+	int			stdout_pipe[2];
+	void			*orig_ctx;
+};
+
+static struct procset *procset;
+
+static struct process_info *get_info(struct process *process)
+{
+	return container_of(process, struct process_info, process);
+}
+
+/* Read as much as possible into the currently-allocated stdout buffer, and
+ * possibly realloc it for the next read */
+static int process_read_stdout_once(struct process_info *procinfo)
+{
+	struct process *process = &procinfo->process;
+	int rc, fd, max_len;
+
+	assert(process->keep_stdout);
+
+	fd = procinfo->stdout_pipe[0];
+
+	max_len =  procinfo->stdout_buf_len - process->stdout_len - 1;
+
+	rc = read(fd, process->stdout_buf + process->stdout_len, max_len);
+	if (rc <= 0)
+		return rc;
+
+	process->stdout_len += rc;
+	if (process->stdout_len == procinfo->stdout_buf_len - 1) {
+		procinfo->stdout_buf_len *= 2;
+		process->stdout_buf = talloc_realloc(procinfo,
+				process->stdout_buf, char,
+				procinfo->stdout_buf_len);
+	}
+
+	return rc;
+}
+
+static int process_setup_stdout_pipe(struct process_info *procinfo)
+{
+	int rc;
+
+	if (!procinfo->process.keep_stdout)
+		return 0;
+
+	procinfo->stdout_buf_len = 4096;
+	procinfo->process.stdout_len = 0;
+	procinfo->process.stdout_buf = talloc_array(procinfo, char,
+			procinfo->stdout_buf_len);
+
+	rc = pipe(procinfo->stdout_pipe);
+	if (rc) {
+		pb_log("pipe failed");
+		return rc;
+	}
+	return 0;
+}
+
+static void process_setup_stdout_parent(struct process_info *procinfo)
+{
+	if (!procinfo->process.keep_stdout)
+		return;
+
+	close(procinfo->stdout_pipe[1]);
+}
+
+static void process_setup_stdout_child(struct process_info *procinfo)
+{
+	int log = fileno(pb_log_get_stream());
+
+	if (procinfo->process.keep_stdout)
+		dup2(procinfo->stdout_pipe[1], STDOUT_FILENO);
+	else
+		dup2(log, STDOUT_FILENO);
+
+	dup2(log, STDERR_FILENO);
+}
+
+static void process_finish_stdout(struct process_info *procinfo)
+{
+	close(procinfo->stdout_pipe[0]);
+	procinfo->process.stdout_buf[procinfo->process.stdout_len] = '\0';
+}
+
+static int process_read_stdout(struct process_info *procinfo)
+{
+	int rc;
+
+	if (!procinfo->process.keep_stdout)
+		return 0;
+
+	do {
+		rc = process_read_stdout_once(procinfo);
+	} while (rc > 0);
+
+	process_finish_stdout(procinfo);
+
+	return rc < 0 ? rc : 0;
+}
+
+static int process_stdout_cb(void *arg)
+{
+	struct process_info *procinfo = arg;
+	int rc;
+
+	rc = process_read_stdout_once(procinfo);
+
+	/* if we're going to signal to the waitset that we're done (ie, non-zero
+	 * return value), then the waiters will remove us, so we drop the
+	 * reference */
+	if (rc < 0) {
+		talloc_unlink(procset, procinfo);
+		procinfo->stdout_waiter = NULL;
+		rc = -1;
+	} else {
+		rc = 0;
+	}
+
+	return rc;
+}
+
+static void sigchld_sigaction(int signo, siginfo_t *info,
+		void *arg __attribute__((unused)))
+{
+	pid_t pid;
+	int rc;
+
+	if (signo != SIGCHLD)
+		return;
+
+	pid = info->si_pid;
+
+	rc = write(procset->sigchld_pipe[1], &pid, sizeof(pid));
+	if (rc != sizeof(pid))
+		pb_log("%s: write failed: %s\n", __func__, strerror(errno));
+}
+
+static int sigchld_pipe_event(void *arg)
+{
+	struct process_info *procinfo;
+	struct procset *procset = arg;
+	struct process *process;
+	int pid, rc;
+
+	rc = read(procset->sigchld_pipe[0], &pid, sizeof(pid));
+	if (rc != sizeof(pid))
+		return 0;
+
+	process = NULL;
+	list_for_each_entry(&procset->async_list, procinfo, async_list) {
+		if (procinfo->process.pid == pid) {
+			process = &procinfo->process;
+			break;
+		}
+	}
+
+	/* We'll receive SIGCHLD for synchronous processes too; just ignore */
+	if (!process)
+		return 0;
+
+	rc = waitpid(process->pid, &process->exit_status, WNOHANG);
+
+	/* if the process is still running, ignore the event. We leave
+	 * the process in async_list so we can manage the final signal */
+	if (rc == 0)
+		return 0;
+
+	/* ensure we have all of the child's stdout */
+	process_read_stdout(procinfo);
+
+	if (process->exit_cb)
+		process->exit_cb(process);
+
+	list_remove(&procinfo->async_list);
+	talloc_unlink(procset, procinfo);
+
+	return 0;
+}
+
+static int process_fini(void *p)
+{
+	struct procset *procset = p;
+	struct sigaction sa;
+
+	memset(&sa, 0, sizeof(sa));
+	sa.sa_handler = SIG_DFL;
+
+	sigaction(SIGCHLD, &sa, NULL);
+
+	waiter_remove(procset->sigchld_waiter);
+
+	close(procset->sigchld_pipe[0]);
+	close(procset->sigchld_pipe[1]);
+	return 0;
+}
+
+struct procset *process_init(void *ctx, struct waitset *set)
+{
+	struct sigaction sa;
+	int rc;
+
+	procset = talloc(ctx, struct procset);
+	procset->waitset = set;
+	list_init(&procset->async_list);
+
+	rc = pipe(procset->sigchld_pipe);
+	if (rc) {
+		pb_log("%s: pipe() failed: %s\n", __func__, strerror(errno));
+		goto err_free;
+	}
+
+	procset->sigchld_waiter = waiter_register_io(set,
+					procset->sigchld_pipe[0], WAIT_IN,
+					sigchld_pipe_event, procset);
+	if (!procset->sigchld_waiter)
+		goto err_close;
+
+	memset(&sa, 0, sizeof(sa));
+	sa.sa_sigaction = sigchld_sigaction;
+	sa.sa_flags = SA_SIGINFO | SA_NOCLDSTOP;
+
+	rc = sigaction(SIGCHLD, &sa, NULL);
+	if (rc) {
+		pb_log("%s: sigaction() failed: %s\n", __func__,
+				strerror(errno));
+		goto err_remove;
+	}
+
+	talloc_set_destructor(procset, process_fini);
+
+	return procset;
+
+err_remove:
+	waiter_remove(procset->sigchld_waiter);
+err_close:
+	close(procset->sigchld_pipe[0]);
+	close(procset->sigchld_pipe[1]);
+err_free:
+	talloc_free(procset);
+	return NULL;
+}
+
+struct process *process_create(void *ctx)
+{
+	struct process_info *info = talloc_zero(ctx, struct process_info);
+	info->orig_ctx = ctx;
+	return &info->process;
+}
+
+void process_release(struct process *process)
+{
+	struct process_info *info = get_info(process);
+	talloc_unlink(info->orig_ctx, info);
+}
+
+static int process_run_common(struct process_info *procinfo)
+{
+	struct process *process = &procinfo->process;
+	const char *arg;
+	char *logmsg;
+	pid_t pid;
+	int rc, i;
+
+	logmsg = talloc_asprintf(procinfo, " exe:  %s\n argv:", process->path);
+	for (i = 0, arg = process->argv[i]; arg; i++, arg = process->argv[i])
+		logmsg = talloc_asprintf_append(logmsg, " '%s'", arg);
+
+	pb_log("Running command:\n%s\n", logmsg);
+
+	rc = process_setup_stdout_pipe(procinfo);
+	if (rc)
+		return rc;
+
+	pid = fork();
+	if (pid < 0) {
+		pb_log("%s: fork failed: %s\n", __func__, strerror(errno));
+		return pid;
+	}
+
+	if (pid == 0) {
+		process_setup_stdout_child(procinfo);
+		execvp(process->path, (char * const *)process->argv);
+		exit(EXIT_FAILURE);
+	}
+
+	process_setup_stdout_parent(procinfo);
+	process->pid = pid;
+
+	return 0;
+}
+
+int process_run_sync(struct process *process)
+{
+	struct process_info *procinfo = get_info(process);
+	int rc;
+
+	rc = process_run_common(procinfo);
+	if (rc)
+		return rc;
+
+	process_read_stdout(procinfo);
+
+	rc = waitpid(process->pid, &process->exit_status, 0);
+	if (rc == -1) {
+		pb_log("%s: waitpid failed: %s\n", __func__, strerror(errno));
+		return rc;
+	}
+
+	return 0;
+}
+
+int process_run_async(struct process *process)
+{
+	struct process_info *procinfo = get_info(process);
+	int rc;
+
+	rc = process_run_common(procinfo);
+	if (rc)
+		return rc;
+
+	if (process->keep_stdout) {
+		procinfo->stdout_waiter = waiter_register_io(procset->waitset,
+						procinfo->stdout_pipe[0],
+						WAIT_IN, process_stdout_cb,
+						procinfo);
+		talloc_reference(procset, procinfo);
+	}
+
+	list_add(&procset->async_list, &procinfo->async_list);
+	talloc_reference(procset, procinfo);
+
+	return 0;
+}
+
+void process_stop_async(struct process *process)
+{
+	kill(process->pid, SIGTERM);
+}
+
+int process_run_simple_argv(void *ctx, const char *argv[])
+{
+	struct process *process;
+	int rc;
+
+	process = process_create(ctx);
+
+	process->path = argv[0];
+	process->argv = argv;
+
+	rc = process_run_sync(process);
+
+	if (!rc)
+		rc = process->exit_status;
+
+	process_release(process);
+
+	return rc;
+}
+
+int process_run_simple(void *ctx, const char *name, ...)
+{
+	int rc, i, n_argv = 1;
+	const char **argv;
+	va_list ap;
+
+	va_start(ap, name);
+	while (va_arg(ap, char *))
+		n_argv++;
+	va_end(ap);
+
+	argv = talloc_array(ctx, const char *, n_argv + 1);
+	argv[0] = name;
+
+	va_start(ap, name);
+	for (i = 1; i < n_argv; i++)
+		argv[i] = va_arg(ap, const char *);
+	va_end(ap);
+
+	argv[i] = NULL;
+
+	rc = process_run_simple_argv(ctx, argv);
+
+	talloc_free(argv);
+
+	return rc;
+}
diff --git a/lib/process/process.h b/lib/process/process.h
new file mode 100644
index 0000000..9e2a2d1
--- /dev/null
+++ b/lib/process/process.h
@@ -0,0 +1,76 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+#ifndef PROCESS_H
+#define PROCESS_H
+
+#include <stdbool.h>
+#include <sys/types.h>
+
+#include <list/list.h>
+#include <waiter/waiter.h>
+
+struct process;
+struct procset;
+
+typedef void	(*process_exit_cb)(struct process *);
+
+struct process {
+	/* caller-provided configuration */
+	const char		*path;
+	const char		**argv;
+	bool			keep_stdout;
+	process_exit_cb		exit_cb;
+	void			*data;
+
+	/* runtime data */
+	pid_t			pid;
+	int			stdout_len;
+	char			*stdout_buf;
+
+	/* post-execution information */
+	int			exit_status;
+};
+
+/* Process management system init. process_init must be called before
+ * process_create. The pointer returned can be talloc_free()-ed, or can be
+ * automatically freed through destruction of the ctx talloc tree.
+ */
+struct procset *process_init(void *ctx, struct waitset *set);
+
+struct process *process_create(void *ctx);
+
+/* process_release: release our reference to the process, but potentially
+ * leave it running. When the process exits, associated resources will
+ * be deallocated.
+ */
+void process_release(struct process *process);
+
+/* Synchronous interface. These functions will all block while waiting for
+ * the process to exit.
+ */
+int process_run_sync(struct process *process);
+int process_run_simple_argv(void *ctx, const char *argv[]);
+int process_run_simple(void *ctx, const char *name, ...)
+	__attribute__((sentinel(0)));
+
+/* Asynchronous interface. When a process is run with process_run_async, the
+ * function returns without wait()ing for the child process to exit. If the
+ * process' exit_cb member is set, that callback will be invoked when the
+ * process exits.
+ */
+int process_run_async(struct process *process);
+
+void process_stop_async(struct process *process);
+#endif /* PROCESS_H */