From: Petr Štetiar <ynezz@true.cz>
Date: Fri, 24 May 2019 11:04:41 +0000 (+0200)
Subject: hotplug: improve error message during group ownership change
X-Git-Url: http://git.openwrt.org/?p=project%2Fprocd.git;a=commitdiff_plain;h=385b904b2f0a50030aaa33417a03f45babf4bd3d

hotplug: improve error message during group ownership change

procd currently outputs following error messages:

 procd: cannot set group dialout for /dev/ttyw8
 procd: cannot set group dialout for /dev/ttyq1
 procd: cannot set group dialout for /dev/ttywf

from which it's not clear where the problem is, if it's either getgrnam
or chown failing and why it's failing so this patch adds name of failed
function and its errno.

Ref: https://github.com/openwrt/openwrt/pull/1773#issuecomment-495555284
Signed-off-by: Petr Štetiar <ynezz@true.cz>
---

diff --git a/plug/hotplug.c b/plug/hotplug.c
index 799123d..fd29e62 100644
--- a/plug/hotplug.c
+++ b/plug/hotplug.c
@@ -25,6 +25,7 @@
 #include <libubox/uloop.h>
 #include <json-c/json.h>
 
+#include <errno.h>
 #include <fcntl.h>
 #include <unistd.h>
 #include <stdlib.h>
@@ -119,6 +120,30 @@ static void mkdir_p(char *dir)
 	}
 }
 
+static void chgrp_error(const char *group, const char *target, const char *failed)
+{
+	ERROR("cannot set group %s for %s (%s: %d)\n",
+	       group, target, failed, errno);
+}
+
+static void chgrp_target(struct blob_attr *bgroup, struct blob_attr *btarget)
+{
+	int ret = 0;
+	struct group *g = NULL;
+	const char *group = blobmsg_get_string(bgroup);
+	const char *target = blobmsg_get_string(btarget);
+
+	errno = 0;
+
+	g = getgrnam(group);
+	if (!g)
+		return chgrp_error(group, target, "getgrnam");
+
+	ret = chown(target, 0, g->gr_gid);
+	if (ret < 0)
+		return chgrp_error(group, target, "chown");
+}
+
 static void handle_makedev(struct blob_attr *msg, struct blob_attr *data)
 {
 	unsigned int oldumask = umask(0);
@@ -131,7 +156,6 @@ static void handle_makedev(struct blob_attr *msg, struct blob_attr *data)
 	char *minor = hotplug_msg_find_var(msg, "MINOR");
 	char *major = hotplug_msg_find_var(msg, "MAJOR");
 	char *subsystem = hotplug_msg_find_var(msg, "SUBSYSTEM");
-	int ret = 0;
 
 	blobmsg_parse_array(mkdev_policy, 3, tb, blobmsg_data(data), blobmsg_data_len(data));
 	if (tb[0] && tb[1] && minor && major && subsystem) {
@@ -147,17 +171,8 @@ static void handle_makedev(struct blob_attr *msg, struct blob_attr *data)
 		mknod(blobmsg_get_string(tb[0]),
 				m | strtoul(blobmsg_data(tb[1]), NULL, 8),
 				makedev(atoi(major), atoi(minor)));
-		if (tb[2]) {
-			struct group *g = getgrnam(blobmsg_get_string(tb[2]));
-
-			if (g)
-				ret = chown(blobmsg_get_string(tb[0]), 0, g->gr_gid);
-
-			if (!g || ret < 0)
-				ERROR("cannot set group %s for %s\n",
-					blobmsg_get_string(tb[2]),
-					blobmsg_get_string(tb[0]));
-		}
+		if (tb[2])
+			chgrp_target(tb[2], tb[0]);
 	}
 	umask(oldumask);
 }