[PATCH v2] pasta.c: modify hostname when detaching new namespace

[PATCH v2] pasta.c: modify hostname when detaching new namespace

[Danish Prakash]

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 | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/pasta.c b/pasta.c
index 31e1e000ee1b..7ce502d3f299 100644
--- a/pasta.c
+++ b/pasta.c
@@ -50,6 +50,8 @@
 #include "netlink.h"
 #include "log.h"
 
+#define HOSTNAME_PREFIX		"pasta-"
+
 /* PID of child, in case we created a namespace */
 int pasta_child_pid;
 
@@ -178,6 +180,7 @@ struct pasta_spawn_cmd_arg {
  */
 static int pasta_spawn_cmd(void *arg)
 {
+	char hostname[HOST_NAME_MAX + 1] = HOSTNAME_PREFIX;
 	const struct pasta_spawn_cmd_arg *a;
 	sigset_t set;
 
@@ -188,6 +191,13 @@ 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 + sizeof(HOSTNAME_PREFIX) - 1, HOST_NAME_MAX + 1 -
+        sizeof(HOSTNAME_PREFIX)) || errno == ENAMETOOLONG) {
+        hostname[HOST_NAME_MAX] = '\0';
+		if (sethostname(hostname, strlen(hostname)))
+			warn("Unable to set pasta-prefixed hostname");
+	}
+
 	/* Wait for the parent to be ready: see main() */
 	sigemptyset(&set);
 	sigaddset(&set, SIGUSR1);
-- 
@@ -50,6 +50,8 @@
 #include "netlink.h"
 #include "log.h"
 
+#define HOSTNAME_PREFIX		"pasta-"
+
 /* PID of child, in case we created a namespace */
 int pasta_child_pid;
 
@@ -178,6 +180,7 @@ struct pasta_spawn_cmd_arg {
  */
 static int pasta_spawn_cmd(void *arg)
 {
+	char hostname[HOST_NAME_MAX + 1] = HOSTNAME_PREFIX;
 	const struct pasta_spawn_cmd_arg *a;
 	sigset_t set;
 
@@ -188,6 +191,13 @@ 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 + sizeof(HOSTNAME_PREFIX) - 1, HOST_NAME_MAX + 1 -
+        sizeof(HOSTNAME_PREFIX)) || errno == ENAMETOOLONG) {
+        hostname[HOST_NAME_MAX] = '\0';
+		if (sethostname(hostname, strlen(hostname)))
+			warn("Unable to set pasta-prefixed hostname");
+	}
+
 	/* Wait for the parent to be ready: see main() */
 	sigemptyset(&set);
 	sigaddset(&set, SIGUSR1);
-- 
2.45.2

Re: [PATCH v2] pasta.c: modify hostname when detaching new namespace

[Stefano Brivio]

On Tue, 30 Jul 2024 11:31:23 +0530
Danish Prakash <contact@danishpraka.sh> wrote:

> 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>

Thanks for following up with this! I just applied it with some coding
style fixes:

> ---
>  pasta.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/pasta.c b/pasta.c
> index 31e1e000ee1b..7ce502d3f299 100644
> --- a/pasta.c
> +++ b/pasta.c
> @@ -50,6 +50,8 @@
>  #include "netlink.h"
>  #include "log.h"
>  
> +#define HOSTNAME_PREFIX		"pasta-"
> +
>  /* PID of child, in case we created a namespace */
>  int pasta_child_pid;
>  
> @@ -178,6 +180,7 @@ struct pasta_spawn_cmd_arg {
>   */
>  static int pasta_spawn_cmd(void *arg)
>  {
> +	char hostname[HOST_NAME_MAX + 1] = HOSTNAME_PREFIX;
>  	const struct pasta_spawn_cmd_arg *a;
>  	sigset_t set;
>  
> @@ -188,6 +191,13 @@ 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 + sizeof(HOSTNAME_PREFIX) - 1, HOST_NAME_MAX + 1 -

This exceeds 80 columns.

> +        sizeof(HOSTNAME_PREFIX)) || errno == ENAMETOOLONG) {

This is indented with spaces instead of tabs, and "errno ==
ENAMETOOLONG" is not aligned with !gethostname(), despite logically
being at the same level.

See also my previous emails about this:
  https://archives.passt.top/passt-dev/20240523162347.44e6faf3@elisabeth/
  https://archives.passt.top/passt-dev/20240524193918.151fd2fc@elisabeth/

> +        hostname[HOST_NAME_MAX] = '\0';

And this should be aligned with the rest of the clause body, that is,
indented one level on top of the conditional. With (two) tabs, not
spaces.

> +		if (sethostname(hostname, strlen(hostname)))
> +			warn("Unable to set pasta-prefixed hostname");
> +	}
> +
>  	/* Wait for the parent to be ready: see main() */
>  	sigemptyset(&set);
>  	sigaddset(&set, SIGUSR1);

-- 
Stefano