svn commit: r274017 - head/sys/kern

[Julian Elischer]

On 11/3/14, 3:46 PM, Mateusz Guzik wrote:
> Author: mjg
> Date: Mon Nov  3 07:46:51 2014
> New Revision: 274017
> URL: https://svnweb.freebsd.org/changeset/base/274017
>
> Log:
>    Provide an on-stack temporary buffer for small ioctl requests.
I'm not sure I like this. We don't know how many more levels
of stack may be needed.
I know that machines are getting faster with more memory,
but the current move towards bloating out the
worries me.  we started out with a single page of stack (SHARED
with the U-area!). I think we are now at several pages.. I forget, is 
it 8?
I'm open to being persuaded but I think we need to have a discussion
about stack usage. We used to say that anything greater that, say
64 bytes should probably be allocated.

> Modified:
>    head/sys/kern/sys_generic.c
>
> Modified: head/sys/kern/sys_generic.c
> ==============================================================================
> --- head/sys/kern/sys_generic.c	Mon Nov  3 07:18:42 2014	(r274016)
> +++ head/sys/kern/sys_generic.c	Mon Nov  3 07:46:51 2014	(r274017)
> @@ -649,6 +649,7 @@ sys_ioctl(struct thread *td, struct ioct
>   	u_long com;
>   	int arg, error;
>   	u_int size;
> +	u_char smalldata[128];
>   	caddr_t data;
>   
>   	if (uap->com > 0xffffffff) {
> @@ -680,17 +681,18 @@ sys_ioctl(struct thread *td, struct ioct
>   			arg = (intptr_t)uap->data;
>   			data = (void *)&arg;
>   			size = 0;
> -		} else
> -			data = malloc((u_long)size, M_IOCTLOPS, M_WAITOK);
> +		} else {
> +			if (size <= sizeof(smalldata))
> +				data = smalldata;
> +			else
> +				data = malloc((u_long)size, M_IOCTLOPS, M_WAITOK);
> +		}
>   	} else
>   		data = (void *)&uap->data;
>   	if (com & IOC_IN) {
>   		error = copyin(uap->data, data, (u_int)size);
> -		if (error) {
> -			if (size > 0)
> -				free(data, M_IOCTLOPS);
> -			return (error);
> -		}
> +		if (error != 0)
> +			goto out;
>   	} else if (com & IOC_OUT) {
>   		/*
>   		 * Zero the buffer so the user always
> @@ -704,7 +706,8 @@ sys_ioctl(struct thread *td, struct ioct
>   	if (error == 0 && (com & IOC_OUT))
>   		error = copyout(data, uap->data, (u_int)size);
>   
> -	if (size > 0)
> +out:
> +	if (size > 0 && data != (caddr_t)&smalldata)
>   		free(data, M_IOCTLOPS);
>   	return (error);
>   }
>
>
>