Re: [PATCH v4 05/13] tpm: add cursor based buffer functions for response parsing

["Jarkko Sakkinen" <jarkko@kernel.org>]

On Tue Apr 4, 2023 at 12:39 AM EEST, James Bottomley wrote:
> Extracting values from returned TPM buffers can be hard.  Add cursor
> based (moving poiner) functions that make it easier to extract TPM
> returned values from a buffer.
>
> Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
>
> ---
> v4: add kernel doc and reword commit
> ---
>  drivers/char/tpm/tpm-buf.c | 48 ++++++++++++++++++++++++++++++++++++++
>  include/linux/tpm.h        |  3 +++
>  2 files changed, 51 insertions(+)
>
> diff --git a/drivers/char/tpm/tpm-buf.c b/drivers/char/tpm/tpm-buf.c
> index b7e42fb6266c..da0f6e725c3f 100644
> --- a/drivers/char/tpm/tpm-buf.c
> +++ b/drivers/char/tpm/tpm-buf.c
> @@ -6,6 +6,8 @@
>  #include <linux/module.h>
>  #include <linux/tpm.h>
>  
> +#include <asm/unaligned.h>
> +
>  static int __tpm_buf_init(struct tpm_buf *buf)
>  {
>  	buf->data = (u8 *)__get_free_page(GFP_KERNEL);
> @@ -229,3 +231,49 @@ void tpm_buf_append_2b(struct tpm_buf *buf, struct tpm_buf *tpm2b)
>  	tpm_buf_reset_int(tpm2b);
>  }
>  EXPORT_SYMBOL_GPL(tpm_buf_append_2b);
> +
> +/* functions for unmarshalling data and moving the cursor */
> +
> +/**
> + * tpm_get_inc_u8 - read a u8 and move pointer beyond it
> + * @ptr: pointer to pointer
> + *
> + * @return: value read
> + */
> +u8 tpm_get_inc_u8(const u8 **ptr)
> +{
> +	return *((*ptr)++);
> +}
> +EXPORT_SYMBOL_GPL(tpm_get_inc_u8);
> +
> +/**
> + * tpm_get_inc_u16 - read a u16 and move pointer beyond it
> + * @ptr: pointer to pointer
> + *
> + * @return: value read (converted from big endian)
> + */
> +u16 tpm_get_inc_u16(const u8 **ptr)
> +{
> +	u16 val;
> +
> +	val = get_unaligned_be16(*ptr);
> +	*ptr += sizeof(val);
> +	return val;
> +}
> +EXPORT_SYMBOL_GPL(tpm_get_inc_u16);
> +
> +/**
> + * tpm_get_inc_u32 - read a u32 and move pointer beyond it
> + * @ptr: pointer to pointer
> + *
> + * @return: value read (converted from big endian)
> + */
> +u32 tpm_get_inc_u32(const u8 **ptr)
> +{
> +	u32 val;
> +
> +	val = get_unaligned_be32(*ptr);
> +	*ptr += sizeof(val);
> +	return val;
> +}
> +EXPORT_SYMBOL_GPL(tpm_get_inc_u32);
> diff --git a/include/linux/tpm.h b/include/linux/tpm.h
> index 76d495cb5b08..845eadfed715 100644
> --- a/include/linux/tpm.h
> +++ b/include/linux/tpm.h
> @@ -336,6 +336,9 @@ void tpm_buf_append_u8(struct tpm_buf *buf, const u8 value);
>  void tpm_buf_append_u16(struct tpm_buf *buf, const u16 value);
>  void tpm_buf_append_u32(struct tpm_buf *buf, const u32 value);
>  void tpm_buf_append_2b(struct tpm_buf *buf, struct tpm_buf *tpm2b);
> +u8 tpm_get_inc_u8(const u8 **ptr);
> +u16 tpm_get_inc_u16(const u8 **ptr);
> +u32 tpm_get_inc_u32(const u8 **ptr);
>  
>  /*
>   * Check if TPM device is in the firmware upgrade mode.
> -- 
> 2.35.3

Why not just inline functions?

BR, Jarkko