svn commit: r274017 - head/sys/kern

[Julian Elischer]

On 11/3/14, 4:21 PM, Julian Elischer wrote:
> 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
... "bloating out the stack" ...
> 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);
>>   }
>>
>>
>>
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