[PATCH] pasta.c: modify hostname when detaching new namespace

[Danish Prakash <contact@danishpraka.sh>]

When invoking pasta without any arguments, it's difficult
to tell whether we are in the new namespace or not leaving
users a bit confused. This change modifies the host namespace
to add a prefix "pasta-" to make it a bit more obvious.

Signed-off-by: Danish Prakash <contact@danishpraka.sh>
---
 pasta.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/pasta.c b/pasta.c
index 31e1e00..840a2b1 100644
--- a/pasta.c
+++ b/pasta.c
@@ -180,6 +180,8 @@ static int pasta_spawn_cmd(void *arg)
 {
 	const struct pasta_spawn_cmd_arg *a;
 	sigset_t set;
+	char hostname[HOST_NAME_MAX+1], pasta_hostname[HOST_NAME_MAX+1];
+	char *hostname_prefix = "pasta-";
 
 	/* We run in a detached PID and mount namespace: mount /proc over */
 	if (mount("", "/proc", "proc", 0, NULL))
@@ -188,6 +190,17 @@ static int pasta_spawn_cmd(void *arg)
 	if (write_file("/proc/sys/net/ipv4/ping_group_range", "0 0"))
 		warn("Cannot set ping_group_range, ICMP requests might fail");
 
+	if (gethostname(hostname, HOST_NAME_MAX+1) == 0) {
+		if ((strlen(hostname) + strlen(hostname_prefix)) > HOST_NAME_MAX) {
+			hostname[strlen(hostname)-strlen(hostname_prefix)] = '\0';
+		}
+		sprintf(pasta_hostname, "%s%s", hostname_prefix, hostname);
+
+		if (sethostname(pasta_hostname, strlen(pasta_hostname)) != 0) {
+			warn("Unable to set pasta-prefixed hostname");
+		}
+	}
+
 	/* Wait for the parent to be ready: see main() */
 	sigemptyset(&set);
 	sigaddset(&set, SIGUSR1);
-- 
@@ -180,6 +180,8 @@ static int pasta_spawn_cmd(void *arg)
 {
 	const struct pasta_spawn_cmd_arg *a;
 	sigset_t set;
+	char hostname[HOST_NAME_MAX+1], pasta_hostname[HOST_NAME_MAX+1];
+	char *hostname_prefix = "pasta-";
 
 	/* We run in a detached PID and mount namespace: mount /proc over */
 	if (mount("", "/proc", "proc", 0, NULL))
@@ -188,6 +190,17 @@ static int pasta_spawn_cmd(void *arg)
 	if (write_file("/proc/sys/net/ipv4/ping_group_range", "0 0"))
 		warn("Cannot set ping_group_range, ICMP requests might fail");
 
+	if (gethostname(hostname, HOST_NAME_MAX+1) == 0) {
+		if ((strlen(hostname) + strlen(hostname_prefix)) > HOST_NAME_MAX) {
+			hostname[strlen(hostname)-strlen(hostname_prefix)] = '\0';
+		}
+		sprintf(pasta_hostname, "%s%s", hostname_prefix, hostname);
+
+		if (sethostname(pasta_hostname, strlen(pasta_hostname)) != 0) {
+			warn("Unable to set pasta-prefixed hostname");
+		}
+	}
+
 	/* Wait for the parent to be ready: see main() */
 	sigemptyset(&set);
 	sigaddset(&set, SIGUSR1);
-- 
2.45.1