On Mon, Jul 18, 2016 at 09:28:50AM +0000, Alexey Gerasev wrote:
> Hello, everybody!
>
> I am trying to port existing program from Linux to Xenomai. This program
> works with CAN devices via CAN raw sockets in single thread, and 'select'
> syscall is used for read/write multiplexing.
> I use Xenomai-3 branch 'stable-3.0.x'. When I try to use 'select' syscall
> on RTCAN sockets, it returns -1 and 'errno' is set to 19 - "No such
> device". I've found that there is no handler for 'select' event in RTCAN
> driver in 'xenomai-3/kernel/drivers/can/rtcan_raw.c' in 'rtcan_driver' at
> line 978.
> Does some fundamental reason for absence of 'rtcan_driver.select' handler
> for RTCAN sockets exist? Or it wasn't implemented just because 'select'
> syscall is rarely used?
>
> I have also tried to implement 'rtcan_driver.select' handler by myself. The
> patch is attached to this message.
> For XNSELECT_READ I use 'rtdm_sem_select' on socket semaphore like it is
> used in RTNet TCP driver in
> 'xenomai-3/kernel/drivers/net/stack/ipv4/tcp/tcp.c' at line 2083. For
> XNSELECT_WRITE I also use 'rtdm_sem_select' on device TX semaphore like in
> 'rtcan_raw_sendmsg' function.
> I have tested this implementation and it seems to be working.
> Please review it.
>
> Best regards,
> Alexey
> -------------- next part --------------
> A non-text attachment was scrubbed...
> Name: rtcan-select.patch
Ok, please, next time, could you put the patch inline in your
e-mail? Anyway, I just have a comment:
diff --git a/kernel/drivers/can/rtcan_raw.c b/kernel/drivers/can/rtcan_raw.c
index 693b927..8ecb5e7 100644
--- a/kernel/drivers/can/rtcan_raw.c
+++ b/kernel/drivers/can/rtcan_raw.c
@@ -964,6 +964,38 @@ ssize_t rtcan_raw_sendmsg(struct rtdm_fd *fd,
return ret;
}
+/***
+ * rtcan_raw_select
+ */
+static int rtcan_raw_select(struct rtdm_fd *fd,
+ rtdm_selector_t *selector,
+ enum rtdm_selecttype type,
+ unsigned fd_index)
+{
+ struct rtcan_socket *sock = rtdm_fd_to_private(fd);
+
+ switch (type) {
+ case XNSELECT_READ:
+ return rtdm_sem_select(&sock->recv_sem, selector, XNSELECT_READ,
fd_index);
+ case XNSELECT_WRITE:
+ {
+ struct rtcan_device *dev;
+ int ifindex = 0;
+
+ if (!(ifindex = atomic_read(&sock->ifindex)))
+ return -ENXIO;
Why do we need that? I mean, either the fd reference count is
sufficient for the interface to be linked unequivocally with the file
descriptor, and this dance is useless, or not, and the fact that you
use atomic_read will not make the race go away: ifindex may well
change between the time you read it, albeit atomically, and the time
you use it.
+
+ if ((dev = rtcan_dev_get_by_index(ifindex)) == NULL)
+ return -ENXIO;
I believe you have taken a reference on the device here, you need
to return it after the call to rtdm_sem_select.
--
Gilles.
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