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

[Nicholas Piggin]

On Wed Jan 18, 2023 at 4:10 PM AEST, Andrew Donnellan wrote:
> From: Russell Currey <ruscur@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> Signed-off-by: Andrew Donnellan <ajd@xxxxxxxxxxxxx>
>
> ---
>
> 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);

Maybe pass the buf size as an argument here? Which is a bit less error
prone and more flexible than finding the right #define for it.

Thanks,
Nick