Re: f_ops flag to speed up compatible ioctls in linux kernel

[filia@softhome.net]

Arjan van de Ven writes: 

> On Wed, Sep 01, 2004 at 03:50:11AM -0600, filia@softhome.net wrote:
>> Hi!  
>> 
>> Stop being arrogant.
>> Can you please elaborate on how to make Linux kernel support e.g. motion 
>> controllers? They do not fit *any* known to me driver interface. They have 
>> several axes, they have about twenty parameters (float or integer), and 
> 
> parameters nicely fit in sysfs. 
> 

 What about errors?
 "set di 200000" might fail for lots of reasons. 

>> they have several commands, a-la start, graceful stop, abrupt stop. Plus 
>> obviously diagnostics - about ten another commands with absolutely 
>> different parameters. And about ten motion monitoring commands. And this is 
>> one example I were need to program. 
> 
> a write() interface doesn't work???
> Hard to believe, you even call them commands.
> fd = open("/dev/funkydevice");
> write(fd, "start"); 
> 
> doesn't sound insane to me 
> 

 it doesn't, since you didn't tryed to make error handling. every thing can 
fail - this is control of mechanics - and it fails often and for a lot of 
reasons. Put here error handling (write(struct whatever) has to return 
another struct whatever2 filled with error description) and thread-safeness. 
Pluss some controllers do support multi-dimensional movements "start 
x,y,z,etc" - and you might have _several_ error structs. Atomicity is 
important for multi-dimensional moves too - move on given axes starts with 
single command. 

 hu? 

 I do not see much point in renaming ioctl() to write() all over the place - 
at least when people see ioctl() they understand that it is not standard 
functionality. write() will for sure confuse a lot of people. 

 --- with respect. best regards.
***    Philips @ Saarbruecken.