[lxc-devel] [PATCH] set the monitor process title to something useful

[Serge Hallyn]

Quoting Tycho Andersen (tycho.andersen at canonical.com):
> Instead of having a parent process that's called whatever the caller of the
> library is called, we instead set it to "[lxc monitor] <lxcpath> <container>"
> 
> Signed-off-by: Tycho Andersen <tycho.andersen at canonical.com>
> ---
>  src/lxc/lxccontainer.c | 10 +++++++++
>  src/lxc/utils.c        | 61 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  src/lxc/utils.h        |  1 +
>  3 files changed, 72 insertions(+)
> 
> diff --git a/src/lxc/lxccontainer.c b/src/lxc/lxccontainer.c
> index 4da1627..1176a6f 100644
> --- a/src/lxc/lxccontainer.c
> +++ b/src/lxc/lxccontainer.c
> @@ -598,6 +598,7 @@ static bool lxcapi_start(struct lxc_container *c, int useinit, char * const argv
>  	* while container is running...
>  	*/
>  	if (daemonize) {
> +		char title[2048];
>  		lxc_monitord_spawn(c->config_path);
>  
>  		pid_t pid = fork();
> @@ -612,6 +613,15 @@ static bool lxcapi_start(struct lxc_container *c, int useinit, char * const argv
>  			return wait_on_daemonized_start(c, pid);
>  		}
>  
> +		/* We don't really care if this doesn't print all the
> +		 * characters; all that it means is that the proctitle will be
> +		 * ugly. Similarly, we also don't care if setproctitle()
> +		 * fails. */
> +
> +		snprintf(title, sizeof(title), "[lxc monitor] %s %s", c->config_path, c->name);
> +		INFO("Attempting to set proc title to %s", title);
> +		setproctitle(title);
> +
>  		/* second fork to be reparented by init */
>  		pid = fork();
>  		if (pid < 0) {
> diff --git a/src/lxc/utils.c b/src/lxc/utils.c
> index 93de1c3..f517ee6 100644
> --- a/src/lxc/utils.c
> +++ b/src/lxc/utils.c
> @@ -39,6 +39,7 @@
>  #include <sys/types.h>
>  #include <sys/wait.h>
>  #include <assert.h>
> +#include <sys/prctl.h>
>  
>  #include "utils.h"
>  #include "log.h"
> @@ -1540,3 +1541,63 @@ char *get_template_path(const char *t)
>  
>  	return tpath;
>  }
> +
> +/*
> + * Sets the process title to the specified title. Note:
> + *   1. this function requires root to succeed
> + *   2. it clears /proc/self/environ
> + *   3. it may not succed (e.g. if title is longer than /proc/self/environ +
> + *      the original title)
> + */
> +int setproctitle(char *title)
> +{
> +	char buf[2048], *tmp;
> +	FILE *f;
> +	int i, len, ret = 0;
> +	unsigned long arg_start, arg_end, env_start, env_end;
> +
> +	f = fopen_cloexec("/proc/self/stat", "r");
> +	if (!f) {
> +		return -1;
> +	}
> +
> +	tmp = fgets(buf, sizeof(buf), f);
> +	fclose(f);
> +	if (!tmp) {
> +		return -1;
> +	}
> +
> +	/* Skip the first 47 fields, column 48-51 are ARG_START and
> +	 * ARG_END. */
> +	tmp = strchr(buf, ' ');
> +	for (i = 0; i < 46; i++)
> +		tmp = strchr(tmp+1, ' ');

Could you add a check here at each step for tmp != NULL?  Or just

	for (i = 0; i < 46 && tmp; i++)
		tmp = strchr(tmp+1, ' ');
	if (!tmp)
		return -1;

> +
> +	i = sscanf(tmp, "%lu %lu %lu %lu", &arg_start, &arg_end, &env_start, &env_end);
> +	if (i != 4) {
> +		return -1;
> +	}
> +
> +	/* We're truncating the environment, so we should use at most the
> +	 * length of the argument + environment for the title. */
> +	len = strlen(title);
> +	if (len > env_end - arg_start) {
> +		arg_end = env_end;
> +		len = env_end - arg_start;
> +	} else {
> +		arg_end = arg_start + len;
> +	}
> +
> +	env_start = arg_end;
> +	env_end = env_start;
> +
> +	/* memcpy instead of strcpy since this isn't null terminated */
> +	memcpy((void*)arg_start, title, len);
> +
> +	ret |= prctl(PR_SET_MM, PR_SET_MM_ARG_START,   (long)arg_start, 0, 0);
> +	ret |= prctl(PR_SET_MM, PR_SET_MM_ARG_END,     (long)arg_end, 0, 0);
> +	ret |= prctl(PR_SET_MM, PR_SET_MM_ENV_START,   (long)env_start, 0, 0);
> +	ret |= prctl(PR_SET_MM, PR_SET_MM_ENV_END,     (long)env_end, 0, 0);
> +
> +	return ret;
> +}
> diff --git a/src/lxc/utils.h b/src/lxc/utils.h
> index b23cd8e..cc18906 100644
> --- a/src/lxc/utils.h
> +++ b/src/lxc/utils.h
> @@ -286,3 +286,4 @@ int print_to_file(const char *file, const char *content);
>  bool switch_to_ns(pid_t pid, const char *ns);
>  int is_dir(const char *path);
>  char *get_template_path(const char *t);
> +int setproctitle(char *title);
> -- 
> 2.1.0
> 
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