Re: [PATCH 03/12] perf tools: Allow BPF program attach to uprobe events

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Fri, Nov 13, 2015 at 12:29:12PM +0000, Wang Nan escreveu:
> This patch appends new syntax to BPF object section name to support
> probing at uprobe event. Now we can use BPF program like this:
> 
>  SEC(
>  "exec=/lib64/libc.so.6\n"
>  "libcwrite=__write"
>  )
>  int libcwrite(void *ctx)
>  {
>      return 1;
>  }
> 
> Where, in section name of a program, before the main config string,
> we can use 'key=value' style options. Now the only option key "exec"
> is for uprobe probing.
> 
> Signed-off-by: Wang Nan <wangnan0@huawei.com>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> Cc: Zefan Li <lizefan@huawei.com>
> Cc: pi3orama@163.com
> ---
>  tools/perf/util/bpf-loader.c | 122 ++++++++++++++++++++++++++++++++++++++++---
>  tools/perf/util/bpf-loader.h |   1 +
>  2 files changed, 117 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/perf/util/bpf-loader.c b/tools/perf/util/bpf-loader.c
> index 4c50411..5f5505d 100644
> --- a/tools/perf/util/bpf-loader.c
> +++ b/tools/perf/util/bpf-loader.c
> @@ -110,6 +110,115 @@ bpf_prog_priv__clear(struct bpf_program *prog __maybe_unused,
>  }
>  
>  static int
> +config__exec(const char *value, struct perf_probe_event *pev)
> +{
> +	pev->uprobes = true;
> +	pev->target = strdup(value);

Shouldn't we check if this fails and return some failure error
accordingly?

> +	return 0;
> +}
> +
> +static struct {
> +	const char *key;
> +	const char *usage;
> +	const char *desc;
> +	int (*func)(const char *, struct perf_probe_event *);
> +} bpf_config_terms[] = {
> +	{
> +		"exec",
> +		"exec=<full path of file>",
> +		"Set uprobe target",
> +		config__exec,
> +	},

Even with the definition of the struct right above it, please use named
initializers, i.e. turn the avove into:

+	{
+		.key	= "exec",
+		.usage  = "exec=<full path of file>",
+		.desc	= "Set uprobe target",
+		.func	= config__exec,
+	},

> +};
> +
> +static int
> +do_config(const char *key, const char *value,
> +	  struct perf_probe_event *pev)
> +{
> +	unsigned int i;
> +
> +	pr_debug("config bpf program: %s=%s\n", key, value);
> +	for (i = 0; i < ARRAY_SIZE(bpf_config_terms); i++)
> +		if (strcmp(key, bpf_config_terms[i].key) == 0)
> +			return bpf_config_terms[i].func(value, pev);
> +
> +	pr_debug("BPF: ERROR: invalid config option in object: %s=%s\n",
> +		 key, value);
> +
> +	pr_debug("\nHint: Currently valid options are:\n");
> +	for (i = 0; i < ARRAY_SIZE(bpf_config_terms); i++)
> +		pr_debug("\t%s:\t%s\n", bpf_config_terms[i].usage,
> +			 bpf_config_terms[i].desc);
> +	pr_debug("\n");
> +
> +	return -BPF_LOADER_ERRNO__CONFIG_TERM;
> +}
> +
> +static const char *
> +parse_config_kvpair(const char *config_str, struct perf_probe_event *pev)
> +{
> +	char *text = strdup(config_str);
> +	char *sep, *line;
> +	const char *main_str = NULL;
> +	int err = 0;
> +
> +	if (!text) {

See, here you do it correctly, checking the strdup() return, providing
some debugging for -v usage _and_ the right ERR_PTR() return, well done!

> +		pr_debug("No enough memory: dup config_str failed\n");
> +		return ERR_PTR(-ENOMEM);
> +	}
> +
> +	line = text;
> +	while ((sep = strchr(line, '\n'))) {
> +		char *equ;
> +
> +		*sep = '\0';
> +		equ = strchr(line, '=');
> +		if (!equ) {
> +			pr_warning("WARNING: invalid config in BPF object: %s\n",
> +				   line);
> +			pr_warning("\tShould be 'key=value'.\n");
> +			goto nextline;
> +		}
> +		*equ = '\0';
> +
> +		err = do_config(line, equ + 1, pev);
> +		if (err)
> +			break;
> +nextline:
> +		line = sep + 1;
> +	}
> +
> +	if (!err)
> +		main_str = config_str + (line - text);
> +	free(text);
> +
> +	if (err)
> +		return ERR_PTR(err);
> +
> +	return main_str;


No biggie, but doing:

	return err ? ERR_PTR(err) : main_str;

Is more compact and clear :-)

> +}
> +
> +static int
> +parse_config(const char *config_str, struct perf_probe_event *pev)
> +{
> +	const char *main_str;
> +	int err;
> +
> +	main_str = parse_config_kvpair(config_str, pev);

Also just for compactness, just a suggestion, doing:

	const char *main_str = parse_config_kvpair(config_str, pev);

Saves screen real state :-)

> +	if (IS_ERR(main_str))
> +		return PTR_ERR(main_str);
> +
> +	err = parse_perf_probe_command(main_str, pev);
> +	if (err < 0) {
> +		pr_debug("bpf: '%s' is not a valid config string\n",
> +			 config_str);
> +		/* parse failed, don't need clear pev. */
> +		return -BPF_LOADER_ERRNO__CONFIG;
> +	}
> +	return 0;
> +}
> +
> +static int
>  config_bpf_program(struct bpf_program *prog)
>  {
>  	struct perf_probe_event *pev = NULL;
> @@ -131,13 +240,9 @@ config_bpf_program(struct bpf_program *prog)
>  	pev = &priv->pev;
>  
>  	pr_debug("bpf: config program '%s'\n", config_str);
> -	err = parse_perf_probe_command(config_str, pev);
> -	if (err < 0) {
> -		pr_debug("bpf: '%s' is not a valid config string\n",
> -			 config_str);
> -		err = -BPF_LOADER_ERRNO__CONFIG;
> +	err = parse_config(config_str, pev);
> +	if (err)
>  		goto errout;
> -	}
>  
>  	if (pev->group && strcmp(pev->group, PERF_BPF_PROBE_GROUP)) {
>  		pr_debug("bpf: '%s': group for event is set and not '%s'.\n",
> @@ -340,6 +445,7 @@ static const char *bpf_loader_strerror_table[NR_ERRNO] = {
>  	[ERRCODE_OFFSET(EVENTNAME)]	= "No event name found in config string",
>  	[ERRCODE_OFFSET(INTERNAL)]	= "BPF loader internal error",
>  	[ERRCODE_OFFSET(COMPILE)]	= "Error when compiling BPF scriptlet",
> +	[ERRCODE_OFFSET(CONFIG_TERM)]	= "Invalid config term in config string",
>  };
>  
>  static int
> @@ -420,6 +526,10 @@ int bpf__strerror_probe(struct bpf_object *obj __maybe_unused,
>  			int err, char *buf, size_t size)
>  {
>  	bpf__strerror_head(err, buf, size);
> +	case BPF_LOADER_ERRNO__CONFIG_TERM: {
> +		scnprintf(buf, size, "%s (add -v to see detail)", emsg);
> +		break;
> +	}
>  	bpf__strerror_entry(EEXIST, "Probe point exist. Try use 'perf probe -d \"*\"'");
>  	bpf__strerror_entry(EACCES, "You need to be root");
>  	bpf__strerror_entry(EPERM, "You need to be root, and /proc/sys/kernel/kptr_restrict should be 0");
> diff --git a/tools/perf/util/bpf-loader.h b/tools/perf/util/bpf-loader.h
> index 9caf3ae..d19f5c5 100644
> --- a/tools/perf/util/bpf-loader.h
> +++ b/tools/perf/util/bpf-loader.h
> @@ -20,6 +20,7 @@ enum bpf_loader_errno {
>  	BPF_LOADER_ERRNO__EVENTNAME,	/* Event name is missing */
>  	BPF_LOADER_ERRNO__INTERNAL,	/* BPF loader internal error */
>  	BPF_LOADER_ERRNO__COMPILE,	/* Error when compiling BPF scriptlet */
> +	BPF_LOADER_ERRNO__CONFIG_TERM,	/* Invalid config term in config term */
>  	__BPF_LOADER_ERRNO__END,
>  };
>  
> -- 
> 1.8.3.4