[PATCH v2] staging: vt6655: use memset to make code clearer

[PATCH v2] staging: vt6655: use memset to make code clearer

[Nam Cao]

A line of code sets the entire struct vnt_rdes0 to zero by treating it as
unsigned int. This works because sizeof(unsigned int) is equal to
sizeof(struct vnt_rdes0) (4 bytes). However it is not obvious what this
code is doing. Re-write this using memset to make the code clearer.

Signed-off-by: Nam Cao <namcaov@gmail.com>
---
v2: re-write commit message because previous message describes a
non-existent problem.

 drivers/staging/vt6655/device_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/staging/vt6655/device_main.c b/drivers/staging/vt6655/device_main.c
index 8e2a976aaaad..a38657769c20 100644
--- a/drivers/staging/vt6655/device_main.c
+++ b/drivers/staging/vt6655/device_main.c
@@ -867,7 +867,7 @@ static bool device_alloc_rx_buf(struct vnt_private *priv,
 		return false;
 	}
 
-	*((unsigned int *)&rd->rd0) = 0; /* FIX cast */
+	memset((void *)&rd->rd0, 0, sizeof(rd->rd0));
 
 	rd->rd0.res_count = cpu_to_le16(priv->rx_buf_sz);
 	rd->rd0.owner = OWNED_BY_NIC;
-- 
2.25.1

Re: [PATCH v2] staging: vt6655: use memset to make code clearer

[Greg KH]

On Fri, Sep 09, 2022 at 11:08:57AM +0200, Nam Cao wrote:
> A line of code sets the entire struct vnt_rdes0 to zero by treating it as
> unsigned int. This works because sizeof(unsigned int) is equal to
> sizeof(struct vnt_rdes0) (4 bytes). However it is not obvious what this
> code is doing. Re-write this using memset to make the code clearer.
> 
> Signed-off-by: Nam Cao <namcaov@gmail.com>
> ---
> v2: re-write commit message because previous message describes a
> non-existent problem.
> 
>  drivers/staging/vt6655/device_main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/staging/vt6655/device_main.c b/drivers/staging/vt6655/device_main.c
> index 8e2a976aaaad..a38657769c20 100644
> --- a/drivers/staging/vt6655/device_main.c
> +++ b/drivers/staging/vt6655/device_main.c
> @@ -867,7 +867,7 @@ static bool device_alloc_rx_buf(struct vnt_private *priv,
>  		return false;
>  	}
>  
> -	*((unsigned int *)&rd->rd0) = 0; /* FIX cast */
> +	memset((void *)&rd->rd0, 0, sizeof(rd->rd0));

Why do you have to cast this to (void *)?  That should almost never be
needed.

thanks,

greg k-h

Re: [PATCH v2] staging: vt6655: use memset to make code clearer

[Nam Cao]

On Fri, Sep 9, 2022 at 12:23 PM Greg KH <gregkh@linuxfoundation.org> wrote:
> Why do you have to cast this to (void *)?  That should almost never be
> needed.

Because I want to suppress a compiler warning:
drivers/staging/vt6655/device_main.c:869:9: warning: passing argument
1 of ‘memset’ discards ‘volatile’ qualifier from pointer target type
[-Wdiscarded-qualifiers]
  869 |  memset(&rd->rd0, 0, sizeof(rd->rd0));
      |         ^~~~~~~~

Best regards,
Nam

Re: [PATCH v2] staging: vt6655: use memset to make code clearer

[Greg KH]

On Fri, Sep 09, 2022 at 01:29:44PM +0200, Nam Cao wrote:
> On Fri, Sep 9, 2022 at 12:23 PM Greg KH <gregkh@linuxfoundation.org> wrote:
> > Why do you have to cast this to (void *)?  That should almost never be
> > needed.
> 
> Because I want to suppress a compiler warning:
> drivers/staging/vt6655/device_main.c:869:9: warning: passing argument
> 1 of ‘memset’ discards ‘volatile’ qualifier from pointer target type
> [-Wdiscarded-qualifiers]
>   869 |  memset(&rd->rd0, 0, sizeof(rd->rd0));
>       |         ^~~~~~~~

Why would that have a type of "volatile"?  That should be fixed first
please.

thanks,

greg k-h