[PATCH 13/35] monitor: disable nvmf-autoconnect udev rules in autoconnect mode

[mwilck at suse.com]

From: Martin Wilck <mwilck at suse.com>

If autoconnect is enabled, disable the respective udev rules
by symlinking /run/udev/rules.d to /dev/null, in order to avoid
the connections being set up by the monitor and the udev workers
at the same time. This is probably the preferred mode of operation
for the monitor.

Users can override this by copying 70-nvmf-autoconnect.rules
from /usr/lib/udev/rules.d to /etc/udev/rules.d (/etc/udev/rules.d
takes precedence over /run/udev/rules.d).

If the symlink can't be created for some reason, autoconnect will
be disabled. There is  only one exception: If
/run/udev/rules.d/70-nvmf-autoconnect.rules already points to
/dev/null at startup, autoconnect can be left on, but the symlink
isn't removed on exit.

Signed-off-by: Martin Wilck <mwilck at suse.com>
---
 monitor.c | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 73 insertions(+), 2 deletions(-)

diff --git a/monitor.c b/monitor.c
index ecf3be2..2a906db 100644
--- a/monitor.c
+++ b/monitor.c
@@ -17,14 +17,18 @@
 
 #include <stddef.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <unistd.h>
 #include <errno.h>
 #include <libudev.h>
 #include <signal.h>
 #include <time.h>
+#include <limits.h>
 #include <syslog.h>
+#include <sys/stat.h>
 #include <sys/epoll.h>
 
+#include "common.h"
 #include "nvme-status.h"
 #include "util/argconfig.h"
 #include "monitor.h"
@@ -33,6 +37,7 @@
 
 static struct monitor_config {
 	bool autoconnect;
+	bool skip_udev_on_exit;
 } mon_cfg;
 
 static struct udev *udev;
@@ -45,6 +50,8 @@ static void close_ptr(int *p)
 	}
 }
 
+CLEANUP_FUNC(char)
+
 static void cleanup_monitor(struct udev_monitor **pmon)
 {
 	if (*pmon) {
@@ -174,12 +181,64 @@ static int monitor_main_loop(struct udev_monitor *monitor)
 	return ret;
 }
 
+static const char autoconnect_rules[] = "/run/udev/rules.d/70-nvmf-autoconnect.rules";
+
+static int monitor_disable_udev_rules(void)
+{
+	CLEANUP(char, path) = strdup(autoconnect_rules);
+	char *s1, *s2;
+	int rc;
+
+	if (!path)
+		return -ENOMEM;
+
+	s2 = strrchr(path, '/');
+	for (s1 = s2 - 1; s1 > path && *s1 != '/'; s1--);
+
+	*s2 = *s1 = '\0';
+	rc = mkdir(path, 0755);
+	if (rc == 0 || errno == EEXIST) {
+		*s1 = '/';
+		rc = mkdir(path, 0755);
+		if (rc == 0 || errno == EEXIST) {
+			*s2 = '/';
+			rc = symlink("/dev/null", path);
+		}
+	}
+	if (rc) {
+		if (errno == EEXIST) {
+			char target[PATH_MAX];
+
+			if (readlink(path, target, sizeof(target)) != -1 &&
+			    !strcmp(target, "/dev/null")) {
+				log(LOG_INFO,
+				    "symlink %s -> /dev/null exists already\n",
+				    autoconnect_rules);
+				return 1;
+			}
+		}
+		log(LOG_ERR, "error creating %s: %m\n", autoconnect_rules);
+	} else
+		log(LOG_INFO, "created %s\n", autoconnect_rules);
+
+	return rc ? (errno ? -errno : -EIO) : 0;
+}
+
+static void monitor_enable_udev_rules(void)
+{
+	if (unlink(autoconnect_rules) == -1 && errno != ENOENT)
+		log(LOG_ERR, "error removing %s: %m\n", autoconnect_rules);
+	else
+		log(LOG_INFO, "removed %s\n", autoconnect_rules);
+}
+
 static int monitor_parse_opts(const char *desc, int argc, char **argv)
 {
 	bool quiet = false;
 	bool verbose = false;
 	bool debug = false;
-	int ret;
+	int ret = 0;
+
 	OPT_ARGS(opts) = {
 		OPT_FLAG("autoconnect",    'A', &mon_cfg.autoconnect, "automatically connect newly discovered controllers"),
 		OPT_FLAG("silent",         'S', &quiet,               "log level: silent"),
@@ -198,7 +257,17 @@ static int monitor_parse_opts(const char *desc, int argc, char **argv)
 		log_level = LOG_INFO;
 	if (debug)
 		log_level = LOG_DEBUG;
-
+	if (mon_cfg.autoconnect) {
+		ret = monitor_disable_udev_rules();
+		if (ret < 0) {
+			mon_cfg.autoconnect = false;
+			log(LOG_WARNING, "autoconnect disabled\n");
+			ret = 0;
+		} else if (ret > 0) {
+			mon_cfg.skip_udev_on_exit = true;
+			ret = 0;
+		}
+	}
 	return ret;
 }
 
@@ -221,6 +290,8 @@ int aen_monitor(const char *desc, int argc, char **argv)
 		udev_monitor_unref(monitor);
 	}
 	udev = udev_unref(udev);
+	if (mon_cfg.autoconnect && !mon_cfg.skip_udev_on_exit)
+		monitor_enable_udev_rules();
 out:
 	return nvme_status_to_errno(ret, true);
 }
-- 
2.29.2