Re: [PATCH v3 04/24] powerpc/secvar: Handle format string in the consumer

["Nicholas Piggin" <npiggin@gmail.com>]

On Wed Jan 18, 2023 at 4:10 PM AEST, Andrew Donnellan wrote:
> From: Russell Currey <ruscur@russell.cc>
>
> The code that handles the format string in secvar-sysfs.c is entirely
> OPAL specific, so create a new "format" op in secvar_operations to make
> the secvar code more generic.  No functional change.
>
> Signed-off-by: Russell Currey <ruscur@russell.cc>
> Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com>
>
> ---
>
> v2: Use sysfs_emit() instead of sprintf() (gregkh)
>
> v3: Enforce format string size limit (ruscur)
> ---
>  arch/powerpc/include/asm/secvar.h            |  3 +++
>  arch/powerpc/kernel/secvar-sysfs.c           | 23 ++++--------------
>  arch/powerpc/platforms/powernv/opal-secvar.c | 25 ++++++++++++++++++++
>  3 files changed, 33 insertions(+), 18 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/secvar.h b/arch/powerpc/include/asm/secvar.h
> index 07ba36f868a7..8b6475589120 100644
> --- a/arch/powerpc/include/asm/secvar.h
> +++ b/arch/powerpc/include/asm/secvar.h
> @@ -11,12 +11,15 @@
>  #include <linux/types.h>
>  #include <linux/errno.h>
>  
> +#define SECVAR_MAX_FORMAT_LEN	30 // max length of string returned by ->format()
> +
>  extern const struct secvar_operations *secvar_ops;
>  
>  struct secvar_operations {
>  	int (*get)(const char *key, u64 key_len, u8 *data, u64 *data_size);
>  	int (*get_next)(const char *key, u64 *key_len, u64 keybufsize);
>  	int (*set)(const char *key, u64 key_len, u8 *data, u64 data_size);
> +	ssize_t (*format)(char *buf);
>  };
>  
>  #ifdef CONFIG_PPC_SECURE_BOOT
> diff --git a/arch/powerpc/kernel/secvar-sysfs.c b/arch/powerpc/kernel/secvar-sysfs.c
> index 462cacc0ca60..d3858eedd72c 100644
> --- a/arch/powerpc/kernel/secvar-sysfs.c
> +++ b/arch/powerpc/kernel/secvar-sysfs.c
> @@ -21,26 +21,13 @@ static struct kset *secvar_kset;
>  static ssize_t format_show(struct kobject *kobj, struct kobj_attribute *attr,
>  			   char *buf)
>  {
> -	ssize_t rc = 0;
> -	struct device_node *node;
> -	const char *format;
> -
> -	node = of_find_compatible_node(NULL, NULL, "ibm,secvar-backend");
> -	if (!of_device_is_available(node)) {
> -		rc = -ENODEV;
> -		goto out;
> -	}
> +	char tmp[SECVAR_MAX_FORMAT_LEN];
> +	ssize_t len = secvar_ops->format(tmp);
>  
> -	rc = of_property_read_string(node, "format", &format);
> -	if (rc)
> -		goto out;
> +	if (len <= 0)
> +		return -EIO;

AFAIKS this does have a functional change, it loses the return value.
Why not return len if it is < 0, and -EIO if len == 0?

Thanks,
Nick