Re: [Outreachy kernel] [PATCH v2] Staging: rtl8188eu: Use put_unaligned_le16

[Preeti U Murthy <preeti@linux.vnet.ibm.com>]

Hi Vaishali,

On 02/18/2015 05:17 PM, Vaishali Thakkar wrote:
> This patch introduces the use of function put_unaligned_le16.

Why is the use of put_unaligned_le16 better than memcpy here ?
Can this be figured out?

Regards
Preeti U Murthy
> 
> This is done using Coccinelle and semantic patch used is as follows:
> 
> @a@
> typedef u16, __le16, uint16_t;
> {u16,__le16,uint16_t} e16;
> identifier tmp;
> expression ptr;
> expression y,e;
> type T;
> @@
> 
> - tmp = cpu_to_le16(y);
> 
> <+... when != tmp
> (
> - memcpy(ptr, (T)&tmp, \(2\|sizeof(u16)\|sizeof(__le16)\|sizeof(uint16_t)\|sizeof(e16)\));
> + put_unaligned_le16(y,ptr);
> |
> - memcpy(ptr, (T)&tmp, ...);
> + put_unaligned_le16(y,ptr);
> )
> ...+>
> ? tmp = e
> 
> @@ type T; identifier a.tmp; @@
> 
> - T tmp;
> ...when != tmp
> 
> Here, use of variable tim_bitmap_le and variable itself is removed. To be compatible
> with changes header file is added too.
> 
> Signed-off-by: Vaishali Thakkar <vthakkar1994@gmail.com>
> ---
> Changes since v1:
> 	-Use of variable tim_bitmap_le is removed
> 	-Variable tim_bitmap_le is removed
> 	-To be compatible with changes header file is added
> 	-Commit log is edited
> 
>  drivers/staging/rtl8188eu/core/rtw_ap.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/staging/rtl8188eu/core/rtw_ap.c b/drivers/staging/rtl8188eu/core/rtw_ap.c
> index da19145..e65ee6e 100644
> --- a/drivers/staging/rtl8188eu/core/rtw_ap.c
> +++ b/drivers/staging/rtl8188eu/core/rtw_ap.c
> @@ -23,6 +23,7 @@
>  #include <drv_types.h>
>  #include <wifi.h>
>  #include <ieee80211.h>
> +#include <asm/unaligned.h>
> 
>  #ifdef CONFIG_88EU_AP_MODE
> 
> @@ -78,11 +79,8 @@ static void update_BCNTIM(struct adapter *padapter)
>  	if (true) {
>  		u8 *p, *dst_ie, *premainder_ie = NULL;
>  		u8 *pbackup_remainder_ie = NULL;
> -		__le16 tim_bitmap_le;
>  		uint offset, tmp_len, tim_ielen, tim_ie_offset, remainder_ielen;
> 
> -		tim_bitmap_le = cpu_to_le16(pstapriv->tim_bitmap);
> -
>  		p = rtw_get_ie(pie + _FIXED_IE_LENGTH_, _TIM_IE_, &tim_ielen, pnetwork_mlmeext->IELength - _FIXED_IE_LENGTH_);
>  		if (p != NULL && tim_ielen > 0) {
>  			tim_ielen += 2;
> @@ -137,9 +135,9 @@ static void update_BCNTIM(struct adapter *padapter)
>  			*dst_ie++ = 0;
> 
>  		if (tim_ielen == 4) {
> -			*dst_ie++ = *(u8 *)&tim_bitmap_le;
> +			*dst_ie++ = pstapriv->tim_bitmap & 0xff;
>  		} else if (tim_ielen == 5) {
> -			memcpy(dst_ie, &tim_bitmap_le, 2);
> +			put_unaligned_le16(pstapriv->tim_bitmap, dst_ie);
>  			dst_ie += 2;
>  		}
>