2022-09-09 09:23:56

by Nam Cao

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

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 <[email protected]>
---
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

2022-09-09 11:00:41

by Greg Kroah-Hartman

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

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 <[email protected]>
> ---
> 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

2022-09-09 12:00:48

by Greg Kroah-Hartman

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

On Fri, Sep 09, 2022 at 01:29:44PM +0200, Nam Cao wrote:
> On Fri, Sep 9, 2022 at 12:23 PM Greg KH <[email protected]> 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

2022-09-09 12:00:55

by Nam Cao

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

On Fri, Sep 9, 2022 at 12:23 PM Greg KH <[email protected]> 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