[openbeos] Re: parallel driver
- From: philippe.houdoin@xxxxxxx
- To: openbeos@xxxxxxxxxxxxx
- Date: Thu, 28 Mar 2002 17:05:19 +0100 (MET)
>> Bear in mind that the ioctl in R5 seems to be broken as it
>> doesn't always pass back the correct error value, so we're
>> having to add parameters to all the structures to pass the
>> error value back.
>
> I didn't know about this, is it experience or did you read
> about this elsewhere ? Btw This is one thing to be corrected
> in R1 :)
From experience.
In a /dev/misc/test R5 driver control hook code:
swith(op) {
case MY_DRIVER_OP:
return B_BAD_VALUE;
...
};
In a userland app:
int fd, rc;
fd = open("/dev/misc/test", O_RDWR);
if (fd < 0)
return;
rc = ioctl(fd, MY_DRIVER_OP, NULL, 0);
printf("ioctl() returns %d\n", rc);
close(fd);
Under both vanilla and BONE R5 BeOS kernels, you will get:
"ioctl() returns -1".
But... B_BAD_VALUE != B_ERROR ;-)
In fact, it's not a BUG at all.
From ioctl() man page:
[...]
RETURN VALUE
Usually, on success zero is returned.
A few ioctls use the return value as an output parameter and return a
nonnegative value on success. On error, -1 is returned, and errno is
set appropriately.
It's just something to remember when you plan to use heavily ioctl()
to communicate with a driver code: you can't use the ioctl() returns value
to sent back a meaningfull result code.
So, one more thing to NOT fix for R1. :-p
-Philippe.
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