Jan Kiszka escreveu:
Rodrigo Rosenfeld Rosas wrote:
Hi Jan, it just happened once and I couldn't reproduce (I didn't want to reproduce it too since I would need to restart my computer because the driver wouldn't unload)...

When it happened I forgot to start the timer running the latency program and

Already running latest SVN version?
Almost there ;) That is why your patch didn't apply cleany, but I just needed to include two "#include" and "#define" lines to drvlib.c or something like...

 rt_timer_start&friends became
deprecated last weekend, so you can't forget this step anymore.
I didn't use rt_timer_start at all. I was doing as you suggested, calling another program to start the timer, like "latency".

my driver failed to load and due to some mistake I've made (I have not indentified it yet), it crashed on rmmoding. I need to check this, but I still think it is a good idea to make the sanity checks...

We need some XENO_ASSERT that is only active when CONFIG_XENO_OPT_DEBUG
is set. I don't want to put such checks in production code, but I see
that they may help debugging early drivers.
I understand your concernings but I really don't think they are relevant... This checks will be much faster then the procedure itself and it would conform to normal munmap behaviour. From man page:

"The address start must be a multiple of the page size. All pages containing a part of the indicated range are unmapped, and subsequent references to these pages will generate SIGSEGV. It is not an error if the indicated range does not contain any mapped pages."

I think that if there was an extra parameter for user_info, it would also verify for validity. BTW, I think there is missing some documentation about the user_info parameter. I had to remember our conversation and look at the code to understand that I should record "current" on this parameter on the moment I called mmap and passing it again on munmap. And it would be good to see the rtdm_user_info_t defined as struct task_struct on the documentation.

I have not written the user-space program yet, so you'll have to wait until monday, when I'll be able to test it, hopefully. But it seems to be working... I changed my driver design. I do the mmap's on driver initialization and just pass the returned addresses on the IOCTL, so I can do them in a RT-context. The problem is that even if the user call an IOCTL to

Hmm, I guess there is still some lacking documentation about what is
possible with RTDM. If you call an IOCTL from RT context, you end up in
the _rt-handler the driver of a device may have registered (if there is
no _rt-handler at all, the _nrt one is invoked, but this is likely not
relevant here).

I assume that you were wondering how to call rtdm_mmap_to_user from this
real-time handler, right?
No. I know it is not possible from the moment. I think I did not explain myself very well. I was wondering how to define a RT mmap like ioctl. As I know I could not use rtdm_mmap_to_user then, I thought in another way of doing it. So I mmaped on driver initialization. On the IOCTL I just passed the already known addresses to the user requesting it. I would have to explain you how these buffers work on V4L2. It is a bit long explanation but I can explain it on other message if you wish.

Well, the trick is to return -ENOSYS for those
IOCTL codes that can only be handled by the _nrt-handler. Xenomai will
then switch your RT task to secondary mode, restart the IOCTL, and the
mmap can safely be executed.
But as I've said, it is not the behaviour I want :)

Well, maybe you do not have any arguments for rtdm_mmap_to_user that
should be influenced by the user's IOCTL.
That is my case.

In this case your current driver design is ok as well. I just wanted to 
underline that it is not necessarily the only way.
But I couldn't find other way of doing it in a RT-context.

munmap, it will still be possible to him to continue using the provided address and this would result in a problem. But, as in all situations, there

When rtdm_munmap is executed, the virtual address range becomes invalid
for the user. Thus any further access to it will raise a segfault.
That's the only problem, but it will not influence the driver integrity.
Yes, that is the problem. Since I only mark as unused on the munmap IOCTL, it would be possible to the user to continue using that address even after the munmap IOCTL call. It I was using a really rtdm_munmap, it wouldn't be possible. It would be a better behaviour, but it would not be run on RT-context. That is the trade-off.

are trade-offs and I prefer to rely on the user, while providing a RT-MMAP-IOCTL. Of course it isn't really a mmap, but if the user don't mess with the pointers, it will work like if it was...

The user can only access the window you mapped in and only as long as it
is mapped.
In my case, it is always mapped to make possible the RT-IOCTLs.
And if you map it read-only, there is even no chance to
destroy potential management structures of the hardware or the driver
within this range.
I do not want to make it read-only because it will probably be very usefull to the user to write on it. The user may want to capture a frame and do some image processing routines on the same memory area when it is possible, avoiding to copy that memory region.
Hope you understood me, I wrote it a little confusing... :)

We will see...
Happy WE,
Happy weekend for you too,


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