Am 06.06.2012 13:20, schrieb Ian Abbott: > On 2012-06-06 10:49, Dan Carpenter wrote: >> On Wed, Jun 06, 2012 at 11:45:43AM +0200, walter harms wrote: >>> >>> >>> Am 06.06.2012 11:28, schrieb Ian Abbott: >>>> On 2012-06-05 12:01, Dan Carpenter wrote: >>>>> On Tue, Jun 05, 2012 at 12:06:10PM +0200, walter harms wrote: >>>>>> Hi all, >>>>>> the patch is fine with me but i have a few basic questions: >>>>>> >>>>>> Why the (void *) at all ? it returns a name what is a const char *. >>>>>> >>>>> >>>>> We're really returning a pointer to a private struct, it's just that >>>>> the first element on the struct always has to be a pointer to char *. >>>> >>>> To be pedantic, it's really returning a pointer to some member of type >>>> 'const char *' within a private struct. To make life easier for >>>> themselves, those drivers make that the first member of the private >>>> struct so a void pointer to the member is also a void pointer to the >>>> struct. >>>> >>> >>> I do not like it. It is confusing. >> >> Yep. > > But at least the confusion is concentrated in a single place! From the > individual drivers' point of view it's fairly simple (as long as it puts > the 'const char pointer to board name' member at the top of its private > data structure). > Sometimes you can not write "clean" code but a few lines of comments are then a must. >>> Are these struct comedi_driver *driv of different size every time ? >> >> Nope. > > It's the private board information data structures for each driver that > are different sizes, but the size is passed in the comedi comedi_driver > 'offset' member along with the 'board_name' and 'num_names' members. Not > all drivers set those members and just use the 'driver_name' to match > any supported device, but I digress. > If i can believe the comments in the structure offset is the distance to the next name /* offset in bytes from one board name pointer to the next */ and the name is not the first entry it is the second. That means any program assuming that this code returns a (struct comedi_driver *) has to do some correction or it will be off-bye-one sizeof(struct comedi_driver *). Please correct me if i am wrong: I have no clue how dev->board_ptr is used, if it works it is fine with me. re, wh _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/devel
