linux-kernel - Re: [PATCH] tpm: Replace scnprintf() with sysfs_emit() and sysfs_emit

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Message-ID: <aFs4H0gT286-cmvC@kernel.org>
Date: Wed, 25 Jun 2025 02:43:27 +0300
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Chelsy Ratnawat <chelsyratnawat2001@...il.com>
Cc: peterhuewe@....de, jgg@...pe.ca, linux-integrity@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tpm: Replace scnprintf() with sysfs_emit() and
 sysfs_emit_at() in sysfs show functions

On Thu, Jun 19, 2025 at 05:37:07AM -0700, Chelsy Ratnawat wrote:
> Replace calls to scnprintf() with sysfs_emit() and sysfs_emit_at() in
> sysfs show functions. These helpers are preferred in sysfs callbacks
> because they automatically handle buffer sizing (PAGE_SIZE) and
> improve safety and readability.
> 
> Signed-off-by: Chelsy Ratnawat <chelsyratnawat2001@...il.com>

Some comments about the commit message.

Don't use "readability" as an argument as it is something that we cannot
measure, and thus useless documentation.

I neither don't understand "PAGE_SIZE" in the parentheses, or how it
"connects" to the sentence. And what do you mean exactly by safety?

Off-topic'ish:

In the Jargon world, safety is actually different than security :-)
Commercial airline planes have great safety (through redundancy)
and not as great (information) security. Just to reflect why
"safety" is neither an argument ...


> ---
>  drivers/char/tpm/tpm_ppi.c | 26 +++++++++++++-------------
>  1 file changed, 13 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_ppi.c b/drivers/char/tpm/tpm_ppi.c
> index bc7b1b4501b3..421c6264bac9 100644
> --- a/drivers/char/tpm/tpm_ppi.c
> +++ b/drivers/char/tpm/tpm_ppi.c
> @@ -52,7 +52,7 @@ static ssize_t tpm_show_ppi_version(struct device *dev,
>  {
>  	struct tpm_chip *chip = to_tpm_chip(dev);
>  
> -	return scnprintf(buf, PAGE_SIZE, "%s\n", chip->ppi_version);
> +	return sysfs_emit(buf, "%s\n", chip->ppi_version);
>  }
>  
>  static ssize_t tpm_show_ppi_request(struct device *dev,
> @@ -87,11 +87,11 @@ static ssize_t tpm_show_ppi_request(struct device *dev,
>  		else {
>  			req = obj->package.elements[1].integer.value;
>  			if (tpm_ppi_req_has_parameter(req))
> -				size = scnprintf(buf, PAGE_SIZE,
> +				size = sysfs_emit(buf,
>  				    "%llu %llu\n", req,
>  				    obj->package.elements[2].integer.value);
>  			else
> -				size = scnprintf(buf, PAGE_SIZE,
> +				size = sysfs_emit(buf,
>  						"%llu\n", req);
>  		}
>  	} else if (obj->package.count == 2 &&
> @@ -100,7 +100,7 @@ static ssize_t tpm_show_ppi_request(struct device *dev,
>  		if (obj->package.elements[0].integer.value)
>  			size = -EFAULT;
>  		else
> -			size = scnprintf(buf, PAGE_SIZE, "%llu\n",
> +			size = sysfs_emit(buf, "%llu\n",
>  				 obj->package.elements[1].integer.value);
>  	}
>  
> @@ -211,9 +211,9 @@ static ssize_t tpm_show_ppi_transition_action(struct device *dev,
>  	}
>  
>  	if (ret < ARRAY_SIZE(info) - 1)
> -		status = scnprintf(buf, PAGE_SIZE, "%d: %s\n", ret, info[ret]);
> +		status = sysfs_emit(buf, "%d: %s\n", ret, info[ret]);
>  	else
> -		status = scnprintf(buf, PAGE_SIZE, "%d: %s\n", ret,
> +		status = sysfs_emit(buf, "%d: %s\n", ret,
>  				   info[ARRAY_SIZE(info)-1]);
>  	return status;
>  }
> @@ -255,22 +255,22 @@ static ssize_t tpm_show_ppi_response(struct device *dev,
>  	res = ret_obj[2].integer.value;
>  	if (req) {
>  		if (res == 0)
> -			status = scnprintf(buf, PAGE_SIZE, "%llu %s\n", req,
> +			status = sysfs_emit(buf, "%llu %s\n", req,
>  					   "0: Success");
>  		else if (res == 0xFFFFFFF0)
> -			status = scnprintf(buf, PAGE_SIZE, "%llu %s\n", req,
> +			status = sysfs_emit(buf, "%llu %s\n", req,
>  					   "0xFFFFFFF0: User Abort");
>  		else if (res == 0xFFFFFFF1)
> -			status = scnprintf(buf, PAGE_SIZE, "%llu %s\n", req,
> +			status = sysfs_emit(buf, "%llu %s\n", req,
>  					   "0xFFFFFFF1: BIOS Failure");
>  		else if (res >= 1 && res <= 0x00000FFF)
> -			status = scnprintf(buf, PAGE_SIZE, "%llu %llu: %s\n",
> +			status = sysfs_emit(buf, "%llu %llu: %s\n",
>  					   req, res, "Corresponding TPM error");
>  		else
> -			status = scnprintf(buf, PAGE_SIZE, "%llu %llu: %s\n",
> +			status = sysfs_emit(buf, "%llu %llu: %s\n",
>  					   req, res, "Error");
>  	} else {
> -		status = scnprintf(buf, PAGE_SIZE, "%llu: %s\n",
> +		status = sysfs_emit(buf, "%llu: %s\n",
>  				   req, "No Recent Request");
>  	}
>  
> @@ -314,7 +314,7 @@ static ssize_t show_ppi_operations(acpi_handle dev_handle, char *buf, u32 start,
>  		}
>  
>  		if (ret > 0 && ret < ARRAY_SIZE(info))
> -			str += scnprintf(str, PAGE_SIZE, "%d %d: %s\n",
> +			str += sysfs_emit_at(str, "%d %d: %s\n",
>  					 i, ret, info[ret]);
>  	}
>  
> -- 
> 2.47.1
> 

BR, Jarkko