Re: [PATCH v4 1/7] libtracefs: Implement tracefs_instances()

["Yordan Karadzhov (VMware)" <y.karadz@gmail.com>]

On 2.07.21 г. 6:54, Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
> 
> Implement tracefs_instances() that will take a regex (or NULL for all) and
> return a list of instances in the system.
> 
> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
> ---
>   include/tracefs.h      |  1 +
>   src/tracefs-instance.c | 78 ++++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 79 insertions(+)
> 
> diff --git a/include/tracefs.h b/include/tracefs.h
> index da8ad4189d4d..a21d2d2f22a6 100644
> --- a/include/tracefs.h
> +++ b/include/tracefs.h
> @@ -44,6 +44,7 @@ int tracefs_instance_file_read_number(struct tracefs_instance *instance,
>   int tracefs_instance_file_open(struct tracefs_instance *instance,
>   			       const char *file, int mode);
>   int tracefs_instances_walk(int (*callback)(const char *, void *), void *context);
> +char **tracefs_instances(const char *regex);
>   
>   bool tracefs_instance_exists(const char *name);
>   bool tracefs_file_exists(struct tracefs_instance *instance, const char *name);
> diff --git a/src/tracefs-instance.c b/src/tracefs-instance.c
> index 2aeb529903bd..d833fae0fb0c 100644
> --- a/src/tracefs-instance.c
> +++ b/src/tracefs-instance.c
> @@ -14,6 +14,7 @@
>   #include <sys/stat.h>
>   #include <fcntl.h>
>   #include <dirent.h>
> +#include <regex.h>
>   #include <limits.h>
>   #include <pthread.h>
>   #include "tracefs.h"
> @@ -630,6 +631,83 @@ out:
>   	return fret;
>   }
>   
> +static inline bool match(const char *str, regex_t *re)
> +{
> +	if (!re)
> +		return true;
> +	return regexec(re, str, 0, NULL, 0) == 0;
> +}
> +
> +struct instance_list {
> +	regex_t		*re;
> +	char		**list;
> +	int		size;
> +	int		failed;
> +};
> +
> +static int build_list(const char *name, void *data)
> +{
> +	struct instance_list *list = data;
> +	char **instances;
> +	int ret = -1;
> +
> +	if (!match(name, list->re))
> +		return 0;
> +
> +	instances = realloc(list->list, list->size + 2);
> +	if (!instances)
> +		goto out;
> +
> +	list->list = instances;
Hi Steven,

I am not sure what was your original intention here, but this doesn't 
seem to work properly. Maybe we need something like this:

	int size =  sizeof(*instances) * (list->size + 2);
	instances = realloc(list->list, size);
	if (!instances)
		goto out;

	instances[list->size + 1] = NULL;




> +	list->list[list->size] = strdup(name);
> +	if (!list->list[list->size])
> +		goto out;
> +
> +	list->size++;
> +	ret = 0;
> +
> + out:
> +	list->failed = ret;
> +	return ret;
> +}
> +
> +/**
> + * tracefs_instances - return a list of instance names
> + * @regex: A regex of instances to filter on (NULL to match all)
> + *
> + * Returns a list of names of existing instances, that must be
> + * freed with tracefs_list_free(). Note, if there are no matches
> + * then an empty list will be returned (not NULL).
> + * NULL on error.
> + */
> +char **tracefs_instances(const char *regex)
> +{
> +	struct instance_list list = { .re = NULL, .list = NULL };
> +	regex_t re;
> +	int ret;
> +
> +	if (regex) {
> +		ret = regcomp(&re, regex, REG_ICASE|REG_NOSUB);
> +		if (ret < 0)
> +			return NULL;
> +		list.re = &re;
> +	}
> +
> +	ret = tracefs_instances_walk(build_list, &list);
> +	if (ret < 0 || list.failed) {
> +		tracefs_list_free(list.list);
> +		list.list = NULL;
> +	} else {
> +		if (!list.list) {
> +			/* No matches should produce an empty list */
> +			list.list = malloc(sizeof(*list.list));
> +			if (list.list)
> +				list.list[0] = NULL;
> +		}

Or you can just do:
				return calloc(1, sizeof(*list.list));

Thanks!
Yordan

> +	}
> +	return list.list;
> +}
> +
>   /**
>    * tracefs_get_clock - Get the current trace clock
>    * @instance: ftrace instance, can be NULL for the top instance
>