Looks good

Reviewed-by Jon Derrick <jonathan.derrick@intel.com>

On Fri, 2019-02-01 at 21:50 +0100, David Kozub wrote:
> From: Jonas Rabenstein <jonas.rabenstein@studium.uni-erlangen.de>
> 
> Split the header generation from the (normal) memcpy part if a
> bytestring is copied into the command buffer. This allows in-place
> generation of the bytestring content. For example, copy_from_user may be
> used without an intermediate buffer.
> 
> Signed-off-by: Jonas Rabenstein <jonas.rabenstein@studium.uni-erlangen.de>
> Reviewed-by: Scott Bauer <sbauer@plzdonthack.me>
> ---
>  block/sed-opal.c | 23 +++++++++++++++--------
>  1 file changed, 15 insertions(+), 8 deletions(-)
> 
> diff --git a/block/sed-opal.c b/block/sed-opal.c
> index 4225f23b2165..4b0a63b9d7c9 100644
> --- a/block/sed-opal.c
> +++ b/block/sed-opal.c
> @@ -586,14 +586,11 @@ static void add_token_u64(int *err, struct opal_dev *cmd, u64 number)
>  		add_token_u8(err, cmd, number >> (len * 8));
>  }
>  
> -static void add_token_bytestring(int *err, struct opal_dev *cmd,
> -				 const u8 *bytestring, size_t len)
> +static u8 *add_bytestring_header(int *err, struct opal_dev *cmd, size_t len)
>  {
>  	size_t header_len = 1;
>  	bool is_short_atom = true;
> -
> -	if (*err)
> -		return;
> +	char *start;
>  
>  	if (len & ~SHORT_ATOM_LEN_MASK) {
>  		header_len = 2;
> @@ -602,17 +599,27 @@ static void add_token_bytestring(int *err, struct opal_dev *cmd,
>  
>  	if (!can_add(err, cmd, header_len + len)) {
>  		pr_debug("Error adding bytestring: end of buffer.\n");
> -		return;
> +		return NULL;
>  	}
>  
>  	if (is_short_atom)
>  		add_short_atom_header(cmd, true, false, len);
>  	else
>  		add_medium_atom_header(cmd, true, false, len);
> +	start = &cmd->cmd[cmd->pos];
> +	return start;
> +}
>  
> -	memcpy(&cmd->cmd[cmd->pos], bytestring, len);
> -	cmd->pos += len;
> +static void add_token_bytestring(int *err, struct opal_dev *cmd,
> +				 const u8 *bytestring, size_t len)
> +{
> +	u8 *start;
>  
> +	start = add_bytestring_header(err, cmd, len);
> +	if (!start)
> +		return;
> +	memcpy(start, bytestring, len);
> +	cmd->pos += len;
>  }
>  
>  static int build_locking_range(u8 *buffer, size_t length, u8 lr)