linux-kernel - Re: [PATCH 1/3] tracing/probes: support '%pd' type for print struct dentry's name

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Date: Fri, 19 Jan 2024 23:57:06 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Ye Bin <yebin10@...wei.com>
Cc: <rostedt@...dmis.org>, <mathieu.desnoyers@...icios.com>,
 <linux-trace-kernel@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] tracing/probes: support '%pd' type for print struct
 dentry's name

On Fri, 19 Jan 2024 09:38:46 +0800
Ye Bin <yebin10@...wei.com> wrote:

> Similar to '%pd' for printk, use 'pd' for print struct dentry's name.

No, please use '%pd' as a type instead.

> 
> Signed-off-by: Ye Bin <yebin10@...wei.com>
> ---
>  kernel/trace/trace_probe.c | 38 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
> 
> diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> index 4dc74d73fc1d..460f98b85b1c 100644
> --- a/kernel/trace/trace_probe.c
> +++ b/kernel/trace/trace_probe.c
> @@ -11,6 +11,7 @@
>   */
>  #define pr_fmt(fmt)	"trace_probe: " fmt
>  
> +#include <linux/dcache.h>
>  #include <linux/bpf.h>
>  #include "trace_btf.h"
>  
> @@ -86,6 +87,8 @@ static const struct fetch_type probe_fetch_types[] = {
>  			    "__data_loc char[]"),
>  	__ASSIGN_FETCH_TYPE("symstr", string, string, sizeof(u32), 1, 1,
>  			    "__data_loc char[]"),
> +	__ASSIGN_FETCH_TYPE("pd", string, string, sizeof(u32), 1, 1,
> +			    "__data_loc char[]"),

And you don't need to add a new type.
Similar to the preprocessor macro, this should be done before parsing the
args. See traceprobe_expand_meta_args(), you can scan the args and search
argument end with ':%pd'. If you find that, you can replace it with 
"+0x%lx(%s):string". Then, you don't need any of these complex fetch type.

Thank you,

>  	/* Basic types */
>  	ASSIGN_FETCH_TYPE(u8,  u8,  0),
>  	ASSIGN_FETCH_TYPE(u16, u16, 0),
> @@ -1090,6 +1093,25 @@ static int __parse_bitfield_probe_arg(const char *bf,
>  	return (BYTES_TO_BITS(t->size) < (bw + bo)) ? -EINVAL : 0;
>  }
>  
> +static char* traceprobe_expand_dentry(const char *argv)
> +{
> +	#define DENTRY_EXPAND_LEN 7  /* +0xXX() */
> +	char *new_argv;
> +	int len = strlen(argv) + 1 + DENTRY_EXPAND_LEN;
> +
> +	new_argv = kmalloc(len, GFP_KERNEL);
> +	if (!new_argv)
> +		return NULL;
> +
> +	if (snprintf(new_argv, len, "+0x%lx(%s)",
> +		     offsetof(struct dentry, d_name.name), argv) >= len) {
> +		kfree(new_argv);
> +		return NULL;
> +	}
> +
> +	return new_argv;
> +}
> +
>  /* String length checking wrapper */
>  static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
>  					   struct probe_arg *parg,
> @@ -1099,6 +1121,7 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
>  	char *t, *t2, *t3;
>  	int ret, len;
>  	char *arg;
> +	char *org_arg = NULL;
>  
>  	arg = kstrdup(argv, GFP_KERNEL);
>  	if (!arg)
> @@ -1182,6 +1205,16 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
>  			 parg->count);
>  	}
>  
> +	if (!strcmp("pd", parg->type->name)) {
> +		char *temp;
> +
> +		temp = traceprobe_expand_dentry(arg);
> +		if (!temp)
> +			goto out;
> +		org_arg = arg;
> +		arg = temp;
> +	}
> +
>  	code = tmp = kcalloc(FETCH_INSN_MAX, sizeof(*code), GFP_KERNEL);
>  	if (!code)
>  		goto out;
> @@ -1243,6 +1276,10 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
>  				goto fail;
>  			}
>  		}
> +
> +		if (!strcmp(parg->type->name, "pd"))
> +			code++;
> +
>  		/* If op == DEREF, replace it with STRING */
>  		if (!strcmp(parg->type->name, "ustring") ||
>  		    code->op == FETCH_OP_UDEREF)
> @@ -1321,6 +1358,7 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
>  	kfree(tmp);
>  out:
>  	kfree(arg);
> +	kfree(org_arg);
>  
>  	return ret;
>  }
> -- 
> 2.31.1
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>