Re: [PATCH v2 1/3] perf/sdt : Listing of SDT markers by perf

[Hemant Kumar]

Hi Andi,

On 07/18/2014 11:20 PM, Andi Kleen wrote:
> Hemant Kumar <hemant@xxxxxxxxxxxxxxxxxx> writes:
>
> First I should say supporting these probes is very useful. Thanks for
> working on this.

Thanks a lot for the appreciation.

> > +
> > +#define SDT_CACHE_DIR "/var/cache/perf/"
> This requires running perf as root, right?

Yes!

> It would be better to use the $HOME cache dir, like the recent JSON patches.

Hmm, seems like a good idea! We can use ~/.debug as Masami suggested.

> > +#define SDT_CACHE "perf-sdt.cache"
> > +#define SDT_CACHE_TMP "perf-sdt.cache.tmp"
> > +
> > +#define DELIM ':'
> > +
> > +struct path_list {
> > +	char path[PATH_MAX];
> > +	struct list_head list;
> > +} execs;
> > +
> > +/* Write operation for cache */
> > +static void write_cache(FILE *cache, char *buffer)
> > +{
> > +	fprintf(cache, "%s", buffer);
> > +}
> > +
> The function seems redundant.

Yeah, right. Will remove it.

> > +/*
> > + * get_sdt_note_info() is the function actually responsible for
> > + * flushing the SDT notes info into the "cache" file or to the
> > + * stdout if "cache" points to NULL. Also, this function finds out
> > + * the build-id of an ELF to be written into "cache".
> > + */
> > +static void get_sdt_note_info(struct list_head *start, const char *target,
> > +			      FILE *cache)
> > +{
> > +	struct sdt_note *pos;
> > +	u8 build_id[BUILD_ID_SIZE];
> > +	char sbuild_id[BUILD_ID_SIZE * 2 + 1];
> > +	char buffer[2 * PATH_MAX];
> > +
> > +	if (list_empty(start))
> > +		return;
> > +
> > +	/* Read the build id of the file */
> > +	if (filename__read_build_id(target, &build_id,
> > +				    sizeof(build_id)) < 0) {
> > +		pr_debug("Couldn't read build-id in %s\n", target);
> pr_info ?

Ok, pr_info will be better.

> > +
> > +/*
> > + * Finds out the libraries present in a system as shown by the command
> > + * "ldconfig --print-cache". Uses "=>" and '/' to find out the start of a
> > + * dso path.
> > + */
> This seems like a hack. How would that handle chroot, containers etc. ?

Right now, it doesn't handle chroot, containers and other path related
stuff. We will have to figure that out!

> > +static inline void append_path(char *path, struct list_head *list)
> > +{
> > +	char *res_path = NULL;
> > +	struct path_list *tmp = NULL;
> > +
> > +	res_path = (char *)malloc(sizeof(char) * PATH_MAX);
> > +
> > +	if (!res_path)
> > +		return;
> > +
> > +	memset(res_path, '\0', PATH_MAX);
> > +
> > +	if (realpath(path, res_path) && !is_present_in_list(list, res_path)) {
>
> O^2 algorithm ?

:) Will improve that by using a hash table.

> > +/*
> > + * Obtain the list of paths from the PATH env variable
> > + */
> Same as above. This probably needs to be more configurable to handle
> more ways to find binaries.

We can make it more configurable, but by default, it should go for
binaries in these directories. What would you suggest?

Thanks a lot for reviewing the patch. :)

--
Thanks,
Hemant Kumar

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