linux-kernel - Re: [PATCH perf/core v10 09/23] perf probe: Show all cached probes

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Date:	Sat, 11 Jun 2016 09:28:09 +0900
From:	Masami Hiramatsu <mhiramat@...nel.org>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	linux-kernel@...r.kernel.org, Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Hemant Kumar <hemant@...ux.vnet.ibm.com>,
	Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
	Brendan Gregg <brendan.d.gregg@...il.com>
Subject: Re: [PATCH perf/core v10 09/23] perf probe: Show all cached probes

On Thu, 9 Jun 2016 11:22:55 -0300
Arnaldo Carvalho de Melo <acme@...nel.org> wrote:

> Em Wed, Jun 08, 2016 at 06:30:30PM +0900, Masami Hiramatsu escreveu:
> > +char *build_id_cache__origname(const char *sbuild_id)
> > +{
> > +	char *linkname;
> > +	char buf[PATH_MAX];
> > +	char *ret = NULL, *p;
> > +	size_t offs = 5;	/* == strlen("../..") */
> > +
> > +	linkname = build_id_cache__linkname(sbuild_id, NULL, 0);
> > +	if (!linkname)
> > +		return NULL;
> > +
> > +	if (readlink(linkname, buf, PATH_MAX) < 0)
> > +		goto out;
> > +	/* The link should be "../..<origpath>/<sbuild_id>" */
> > +	p = strrchr(buf, '/');	/* Cut off the "/<sbuild_id>" */
> > +	if (p && (p > buf + offs)) {
> > +		*p = '\0';
> > +		if (buf[offs + 1] == '[')
> > +			offs++;	/*
> > +				 * This is a DSO name, like [kernel.kallsyms].
> > +				 * Skip the first '/', since this is not the
> > +				 * cache of a regular file.
> > +				 */
> > +		ret = strdup(buf + offs);	/* Skip "../..[/]" */
> 
> strdup can fail.

Ah, right.

> 
> > +	}
> > +out:
> > +	free(linkname);
> > +	return ret;
> > +}
> > +
> >  static const char *build_id_cache__basename(bool is_kallsyms, bool is_vdso)
> >  {
> >  	return is_kallsyms ? "kallsyms" : (is_vdso ? "vdso" : "elf");
> > @@ -390,6 +419,59 @@ void disable_buildid_cache(void)
> >  	no_buildid_cache = true;
> >  }
> >  
> > +int build_id_cache__list_all(struct strlist **result)
> > +{
> > +	struct strlist *toplist, *list, *bidlist;
> > +	struct str_node *nd, *nd2;
> > +	char *topdir, *linkdir;
> > +	char sbuild_id[SBUILD_ID_SIZE];
> > +	int ret = 0;
> > +
> > +	/* Open the top-level directory */
> > +	if (asprintf(&topdir, "%s/.build-id/", buildid_dir) < 0)
> > +		return -errno;
> 
> Wouldn't be better to just return -1 and leave the caller to look at
> errno? I know that there is code that does that, but better stick to the
> errno convention?

Hmm, IMHO, that may depends on case. This case is possible,
but in below case, pr_debug() also calls libc function and
it can override the errno. This can also happen when we run
some cleanup code before returning.

So, I think it will be good for enough small functions, but
not good for complex bigger functions.

>From the viewpoint of debugging, maybe it is also possible
to return -N, where N is based on the place where the error
happens :)

> > +	toplist = lsdir(topdir, lsdir_no_dot_filter);
> > +	if (!toplist) {
> > +		pr_debug("Failed to opendir %s\n", topdir);
> > +		ret = -errno;
> 
> ditto
> 
> > +		goto out;
> > +	}
> > +	bidlist = strlist__new(NULL, NULL);
> > +	strlist__for_each(nd, toplist) {
> > +		if (asprintf(&linkdir, "%s/%s", topdir, nd->s) < 0) {
> > +			ret = -errno;
> > +			goto out;
> > +		}
> > +		/* Open the lower-level directory */
> > +		list = lsdir(linkdir, lsdir_no_dot_filter);
> > +		if (!list) {
> > +			pr_debug("Failed to open %s: %d\n", linkdir, -errno);
> > +			goto next;
> > +		}
> > +		strlist__for_each(nd2, list) {
> > +			ret = snprintf(sbuild_id, SBUILD_ID_SIZE, "%s%s",
> > +					nd->s, nd2->s);
> > +			if (ret != SBUILD_ID_SIZE - 1) {
> > +				pr_debug("%s/%s is not buildid cache\n",
> > +					nd->s, nd2->s);
> > +				continue;
> > +			}
> > +			strlist__add(bidlist, sbuild_id);
> 
> strlist__add() can fail, please check its result.

Ah, I forgot to update that...

> 
> > +		}
> > +		strlist__delete(list);
> > +next:
> > +		free(linkdir);
> > +	}
> > +
> > +	*result = bidlist;
> > +out:
> > +	if (toplist)
> > +		strlist__delete(toplist);
> 
> No need for checking toplist.

OK.

> 
> > +	free(topdir);
> > +
> > +	return ret;
> > +}
> 
> <SNIP>
> 
> - Arnaldo

Thank you!

-- 
Masami Hiramatsu <mhiramat@...nel.org>