zdev: Implement --no-settle

There are some situations where running "udevadm settle" can result in
a deadlock, such as in the early stages of initial RAM-disk processing.

Introduce a new command-line option --no-settle that can be used to
suppress calling "udevadm settle" to allow chzdev to be run in such
situations.

Signed-off-by: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

zdev/src/chzdev.c

@@ -95,6 +95,7 @@ struct options {
 	struct util_list *base;		/* List of struct strlist_node */
 	unsigned int verbose:1;
 	unsigned int quiet:1;
+	unsigned int no_settle:1;
 };
 
 /* Makefile converts chzdev_usage.txt into C file which we include here. */
@@ -136,6 +137,7 @@ enum {
 	OPT_VERSION		= 'v',
 	OPT_VERBOSE		= 'V',
 	OPT_QUIET		= 'q',
+	OPT_NO_SETTLE		= (OPT_ANONYMOUS_BASE+__COUNTER__),
 };
 
 static struct opts_conflict conflict_list[] = {
@@ -217,6 +219,7 @@ static const struct option opt_list[] = {
 	{ "base",		required_argument, NULL, OPT_BASE },
 	{ "verbose",		no_argument,	NULL, OPT_VERBOSE },
 	{ "quiet",		no_argument,	NULL, OPT_QUIET },
+	{ "no-settle",		no_argument,	NULL, OPT_NO_SETTLE },
 	{ NULL,			no_argument,	NULL, 0 },
 };
 
@@ -937,6 +940,11 @@ static exit_code_t parse_options(struct options *opts, int argc, char *argv[])
 			opts->quiet = 1;
 			break;
 
+		case OPT_NO_SETTLE:
+			/* --no-settle */
+			opts->no_settle = 1;
+			break;
+
 		case ':':
 			/* Missing option argument. */
 			syntax("Option '%s' requires an argument\n",
@@ -2904,6 +2912,7 @@ int main(int argc, char *argv[])
 	force	= opts.force;
 	yes	= opts.yes;
 	dryrun	= opts.dryrun;
+	udev_no_settle = opts.no_settle;
 	path_set_base(opts.base);
 
 	if (dryrun)

zdev/src/chzdev_usage.txt

@@ -54,5 +54,6 @@ OPTIONS
       --no-root-update   Skip root device update
       --dry-run          Display changes without applying
       --base PATH        Use PATH as base for accessing files
+      --no-settle        Do not wait for udev to settle
   -V, --verbose          Print additional run-time information
   -q, --quiet            Print only minimal run-time information

zdev/src/udev.c

@@ -24,6 +24,7 @@
 #include "udev.h"
 
 int udev_need_settle = 0;
+int udev_no_settle;
 
 /* Create a newly allocated udev entry. */
 static struct udev_entry_node *udev_entry_node_new(const char *key,
@@ -403,5 +404,7 @@ exit_code_t udev_remove_rule(const char *type, const char *id)
 /* Wait for all current udev events to finish. */
 void udev_settle(void)
 {
+	if (udev_no_settle)
+		return;
 	misc_system(err_ignore, "%s settle", PATH_UDEVADM);
 }