[PATCH 1/4] drivers/net/enic: decrement sizeof size in strncmp

[PATCH 1/4] drivers/net/enic: decrement sizeof size in strncmp

[Julia Lawall]

From: Julia Lawall <julia@diku.dk>

As observed by Joe Perches, sizeof of a constant string includes the
trailing 0.  If what is wanted is to check the initial characters of
another string, this trailing 0 should not be taken into account.  If an
exact match is wanted, strcmp should be used instead.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@
expression foo;
constant char *abc;
@@

strncmp(foo, abc, 
- sizeof(abc)
+ sizeof(abc)-1
 )
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>

---
 drivers/net/enic/vnic_dev.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff -u -p a/drivers/net/enic/vnic_dev.c b/drivers/net/enic/vnic_dev.c
--- a/drivers/net/enic/vnic_dev.c
+++ b/drivers/net/enic/vnic_dev.c
@@ -358,9 +358,9 @@ int vnic_dev_hw_version(struct vnic_dev 
 	if (err)
 		return err;
 
-	if (strncmp(fw_info->hw_version, "A1", sizeof("A1")) == 0)
+	if (strncmp(fw_info->hw_version, "A1", sizeof("A1") - 1) == 0)
 		*hw_ver = VNIC_DEV_HW_VER_A1;
-	else if (strncmp(fw_info->hw_version, "A2", sizeof("A2")) == 0)
+	else if (strncmp(fw_info->hw_version, "A2", sizeof("A2") - 1) == 0)
 		*hw_ver = VNIC_DEV_HW_VER_A2;
 	else
 		*hw_ver = VNIC_DEV_HW_VER_UNKNOWN;

Re: [PATCH 1/4] drivers/net/enic: decrement sizeof size in strncmp

[Jörg-Volker Peetz]

Julia Lawall wrote:
<snip>
> strncmp(foo, abc, 
> - sizeof(abc)
> + sizeof(abc)-1
>  )
<snip>
> -	if (strncmp(fw_info->hw_version, "A1", sizeof("A1")) == 0)
> +	if (strncmp(fw_info->hw_version, "A1", sizeof("A1") - 1) == 0)
>  		*hw_ver = VNIC_DEV_HW_VER_A1;
> -	else if (strncmp(fw_info->hw_version, "A2", sizeof("A2")) == 0)
> +	else if (strncmp(fw_info->hw_version, "A2", sizeof("A2") - 1) == 0)
<snip>
Why not use strlen(abc) instead of sizeof(abc) - 1 ?
-- 
Regards,
Jörg-Volker.

Re: [PATCH 1/4] drivers/net/enic: decrement sizeof size in strncmp

[Jörg-Volker Peetz]

Julia Lawall wrote:
> From: Julia Law all <julia@diku.dk>
> 
> As observed by Joe Perches, sizeof of a constant string includes the
> trailing 0.  If what is wanted is to check the initial characters of
> another string, this trailing 0 should not be taken into account.  If an
> exact match is wanted, strcmp should be used instead.
> 
> The semantic patch that makes this change is as follows:
> (http://coccinelle.lip6.fr/)
> 
> // <smpl>
> @@
> expression foo;
> constant char *abc;
> @@
> 
> strncmp(foo, abc, 
> - sizeof(abc)
> + sizeof(abc)-1
>  )
> // </smpl>
> 
<snip>
How about this pattern (uses length of first argument):

strncmp(foo, abc,
- sizeof(foo)

?
-- 
Best regards,
Jörg-Volker.

Re: [PATCH 1/4] drivers/net/enic: decrement sizeof size in strncmp

[Scott Feldman]

Thanks Julia/Jorg.  We'll pick up change in next enic patch series.

-scott


On 11/11/09 11:48 PM, "Julia Lawall" <julia@diku.dk> wrote:

> From: Julia Lawall <julia@diku.dk>
> 
> As observed by Joe Perches, sizeof of a constant string includes the
> trailing 0.  If what is wanted is to check the initial characters of
> another string, this trailing 0 should not be taken into account.  If an
> exact match is wanted, strcmp should be used instead.
> 
> The semantic patch that makes this change is as follows:
> (http://coccinelle.lip6.fr/)
> 
> // <smpl>
> @@
> expression foo;
> constant char *abc;
> @@
> 
> strncmp(foo, abc,
> - sizeof(abc)
> + sizeof(abc)-1
>  )
> // </smpl>
> 
> Signed-off-by: Julia Lawall <julia@diku.dk>
> 
> ---
>  drivers/net/enic/vnic_dev.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff -u -p a/drivers/net/enic/vnic_dev.c b/drivers/net/enic/vnic_dev.c
> --- a/drivers/net/enic/vnic_dev.c
> +++ b/drivers/net/enic/vnic_dev.c
> @@ -358,9 +358,9 @@ int vnic_dev_hw_version(struct vnic_dev
> if (err)
> return err;
>  
> - if (strncmp(fw_info->hw_version, "A1", sizeof("A1")) == 0)
> + if (strncmp(fw_info->hw_version, "A1", sizeof("A1") - 1) == 0)
> *hw_ver = VNIC_DEV_HW_VER_A1;
> - else if (strncmp(fw_info->hw_version, "A2", sizeof("A2")) == 0)
> + else if (strncmp(fw_info->hw_version, "A2", sizeof("A2") - 1) == 0)
> *hw_ver = VNIC_DEV_HW_VER_A2;
> else
> *hw_ver = VNIC_DEV_HW_VER_UNKNOWN;