[PATCH] drivers: video: Remove useless checks

[PATCH] drivers: video: Remove useless checks

[Maxin B John]

Comparing unsigned less than zero will never be true.
Removing similar checks from 'fbmem.c' and 'fbcmap.c'.

Please let me know your comments.

Signed-off-by: Maxin B. John <maxin.john@gmail.com>
---
diff --git a/drivers/video/fbcmap.c b/drivers/video/fbcmap.c
index 5c3960d..15cf8fc 100644
--- a/drivers/video/fbcmap.c
+++ b/drivers/video/fbcmap.c
@@ -285,8 +285,7 @@ int fb_set_user_cmap(struct fb_cmap_user *cmap, struct fb_info *info)
 		rc = -ENODEV;
 		goto out;
 	}
-	if (cmap->start < 0 || (!info->fbops->fb_setcolreg &&
-				!info->fbops->fb_setcmap)) {
+	if (!info->fbops->fb_setcolreg && !info->fbops->fb_setcmap) {
 		rc = -EINVAL;
 		goto out1;
 	}
diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
index 5aac00e..9edca4d 100644
--- a/drivers/video/fbmem.c
+++ b/drivers/video/fbmem.c
@@ -1143,7 +1143,7 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
 			return -EFAULT;
 		if (con2fb.console < 1 || con2fb.console > MAX_NR_CONSOLES)
 			return -EINVAL;
-		if (con2fb.framebuffer < 0 || con2fb.framebuffer >= FB_MAX)
+		if (con2fb.framebuffer >= FB_MAX)
 			return -EINVAL;
 		if (!registered_fb[con2fb.framebuffer])
 			request_module("fb%d", con2fb.framebuffer);

Re: [PATCH] drivers: video: Remove useless checks

[Maxin B John]

Hi Paul,

Please let me know your comments on this patch.

Best Regards,
Maxin

On Thu, May 19, 2011 at 9:27 PM, Maxin B John <maxin.john@gmail.com> wrote:
> Comparing unsigned less than zero will never be true.
> Removing similar checks from 'fbmem.c' and 'fbcmap.c'.
>
> Please let me know your comments.
>
> Signed-off-by: Maxin B. John <maxin.john@gmail.com>
> ---
> diff --git a/drivers/video/fbcmap.c b/drivers/video/fbcmap.c
> index 5c3960d..15cf8fc 100644
> --- a/drivers/video/fbcmap.c
> +++ b/drivers/video/fbcmap.c
> @@ -285,8 +285,7 @@ int fb_set_user_cmap(struct fb_cmap_user *cmap, struct fb_info *info)
>                rc = -ENODEV;
>                goto out;
>        }
> -       if (cmap->start < 0 || (!info->fbops->fb_setcolreg &&
> -                               !info->fbops->fb_setcmap)) {
> +       if (!info->fbops->fb_setcolreg && !info->fbops->fb_setcmap) {
>                rc = -EINVAL;
>                goto out1;
>        }
> diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
> index 5aac00e..9edca4d 100644
> --- a/drivers/video/fbmem.c
> +++ b/drivers/video/fbmem.c
> @@ -1143,7 +1143,7 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
>                        return -EFAULT;
>                if (con2fb.console < 1 || con2fb.console > MAX_NR_CONSOLES)
>                        return -EINVAL;
> -               if (con2fb.framebuffer < 0 || con2fb.framebuffer >= FB_MAX)
> +               if (con2fb.framebuffer >= FB_MAX)
>                        return -EINVAL;
>                if (!registered_fb[con2fb.framebuffer])
>                        request_module("fb%d", con2fb.framebuffer);
>

Re: [PATCH] drivers: video: Remove useless checks

[Tim Gardner]

On 05/19/2011 12:27 PM, Maxin B John wrote:
> Comparing unsigned less than zero will never be true.
> Removing similar checks from 'fbmem.c' and 'fbcmap.c'.
>
> Please let me know your comments.
>
> Signed-off-by: Maxin B. John<maxin.john@gmail.com>
> ---
> diff --git a/drivers/video/fbcmap.c b/drivers/video/fbcmap.c
> index 5c3960d..15cf8fc 100644
> --- a/drivers/video/fbcmap.c
> +++ b/drivers/video/fbcmap.c
> @@ -285,8 +285,7 @@ int fb_set_user_cmap(struct fb_cmap_user *cmap, struct fb_info *info)
>   		rc = -ENODEV;
>   		goto out;
>   	}
> -	if (cmap->start<  0 || (!info->fbops->fb_setcolreg&&
> -				!info->fbops->fb_setcmap)) {
> +	if (!info->fbops->fb_setcolreg&&  !info->fbops->fb_setcmap) {
>   		rc = -EINVAL;
>   		goto out1;
>   	}
> diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
> index 5aac00e..9edca4d 100644
> --- a/drivers/video/fbmem.c
> +++ b/drivers/video/fbmem.c
> @@ -1143,7 +1143,7 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
>   			return -EFAULT;
>   		if (con2fb.console<  1 || con2fb.console>  MAX_NR_CONSOLES)
>   			return -EINVAL;
> -		if (con2fb.framebuffer<  0 || con2fb.framebuffer>= FB_MAX)
> +		if (con2fb.framebuffer>= FB_MAX)
>   			return -EINVAL;
>   		if (!registered_fb[con2fb.framebuffer])
>   			request_module("fb%d", con2fb.framebuffer);
>

Looks right to me, though there are other places that suffer from the 
same issue. See fb_set_cmap() and its use of 'int start' and cmap->start.

rtg
-- 
Tim Gardner tim.gardner@canonical.com

Re: [PATCH] drivers: video: Remove useless checks

[Maxin B John]

Hi,

On Wed, May 25, 2011 at 1:47 PM, Tim Gardner <tim.gardner@canonical.com> wrote:
> On 05/19/2011 12:27 PM, Maxin B John wrote:
>>
>> Comparing unsigned less than zero will never be true.
>> Removing similar checks from 'fbmem.c' and 'fbcmap.c'.
>
> Looks right to me, though there are other places that suffer from the same
> issue. See fb_set_cmap() and its use of 'int start' and cmap->start.

Thank you very much for reviewing the patch. As per your suggestion, I
have checked
the scenario is fb_set_cmap() and the use of 'int start' and 'cmap->start'.

IMHO, that scenario doesn't fall under the comparison of unsigned int
< 0. That scenario
looks similar to the below given code to me:
/*---------------------------------*/
#include <stdio.h>

int
main ()
{
  unsigned int u_int = -1;
  int s_int = 0;
  s_int = u_int;
  if (s_int < 0)
    printf ("s_int is less than 0\n");
  return 0;
}
/*---------------------------------*/

Please let me know your comments.

Best Regards,
Maxin

Re: [PATCH] drivers: video: Remove useless checks

[Tim Gardner]

On 05/26/2011 03:30 AM, Maxin B John wrote:
> Hi,
>
> On Wed, May 25, 2011 at 1:47 PM, Tim Gardner<tim.gardner@canonical.com>  wrote:
>> On 05/19/2011 12:27 PM, Maxin B John wrote:
>>>
>>> Comparing unsigned less than zero will never be true.
>>> Removing similar checks from 'fbmem.c' and 'fbcmap.c'.
>>
>> Looks right to me, though there are other places that suffer from the same
>> issue. See fb_set_cmap() and its use of 'int start' and cmap->start.
>
> Thank you very much for reviewing the patch. As per your suggestion, I
> have checked
> the scenario is fb_set_cmap() and the use of 'int start' and 'cmap->start'.
>
> IMHO, that scenario doesn't fall under the comparison of unsigned int
> <  0. That scenario
> looks similar to the below given code to me:
> /*---------------------------------*/
> #include<stdio.h>
>
> int
> main ()
> {
>    unsigned int u_int = -1;
>    int s_int = 0;
>    s_int = u_int;
>    if (s_int<  0)
>      printf ("s_int is less than 0\n");
>    return 0;
> }
> /*---------------------------------*/
>
> Please let me know your comments.
>
> Best Regards,
> Maxin
>

IMHO mixing signed and unsigned comparisons like this is just wrong. Its 
unnecessarily complicated and misleading, especially for a device 
driver. I'm a firm believer in the KISS philosophy for driver development.

Its likely that the reason the fb code got into this situation is 
because a type was changed from signed to unsigned whence long ago, and 
nobody has bothered to clean it up.

rtg
-- 
Tim Gardner tim.gardner@canonical.com

Re: [PATCH] drivers: video: Remove useless checks

[Maxin B John]

Hi,

> IMHO mixing signed and unsigned comparisons like this is just wrong. Its
> unnecessarily complicated and misleading, especially for a device driver.

Yes. I do agree with you.

> Its likely that the reason the fb code got into this situation is because a
> type was changed from signed to unsigned whence long ago, and nobody has
> bothered to clean it up.

Thats possible. Similar useless checks are present in other subsystems
of the kernel as well.

WBR,
Maxin

Re: [PATCH] drivers: video: Remove useless checks

[Maxin B John]

ping ...

On Thu, May 19, 2011 at 7:27 PM, Maxin B John <maxin.john@gmail.com> wrote:
> Comparing unsigned less than zero will never be true.
> Removing similar checks from 'fbmem.c' and 'fbcmap.c'.
>
> Please let me know your comments.
>
> Signed-off-by: Maxin B. John <maxin.john@gmail.com>
> ---
> diff --git a/drivers/video/fbcmap.c b/drivers/video/fbcmap.c
> index 5c3960d..15cf8fc 100644
> --- a/drivers/video/fbcmap.c
> +++ b/drivers/video/fbcmap.c
> @@ -285,8 +285,7 @@ int fb_set_user_cmap(struct fb_cmap_user *cmap, struct fb_info *info)
>                rc = -ENODEV;
>                goto out;
>        }
> -       if (cmap->start < 0 || (!info->fbops->fb_setcolreg &&
> -                               !info->fbops->fb_setcmap)) {
> +       if (!info->fbops->fb_setcolreg && !info->fbops->fb_setcmap) {
>                rc = -EINVAL;
>                goto out1;
>        }
> diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
> index 5aac00e..9edca4d 100644
> --- a/drivers/video/fbmem.c
> +++ b/drivers/video/fbmem.c
> @@ -1143,7 +1143,7 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
>                        return -EFAULT;
>                if (con2fb.console < 1 || con2fb.console > MAX_NR_CONSOLES)
>                        return -EINVAL;
> -               if (con2fb.framebuffer < 0 || con2fb.framebuffer >= FB_MAX)
> +               if (con2fb.framebuffer >= FB_MAX)
>                        return -EINVAL;
>                if (!registered_fb[con2fb.framebuffer])
>                        request_module("fb%d", con2fb.framebuffer);
>

Re: [PATCH] drivers: video: Remove useless checks

[Joe Perches]

On Fri, 2011-06-03 at 10:29 +0100, Maxin B John wrote:
> ping ...
> On Thu, May 19, 2011 at 7:27 PM, Maxin B John <maxin.john@gmail.com> wrote:
> > Comparing unsigned less than zero will never be true.
> > Removing similar checks from 'fbmem.c' and 'fbcmap.c'.
> > Please let me know your comments.

http://lkml.org/lkml/2004/11/23/171