[libhid-discuss] libhid problems with interrupt_read/write

[Thomas Maclean]

Greetings:

Please excuse me if this is the wrong forum to ask about libhid usage
problems ...

I am trying to debug a problem I am having with Bruce Perens' Ion
software, which uses libhid to access a USB HID-connected home automation
controller.  (See http://www.perens.com/Ion/ )

The software uses hid_interrupt_write and and
hid_interrupt_read to access the controller.  I am using libhid-svn
(changelist 330) on a Centos 4 platform  (a redhat clone), with
libusb-0.1.8-3.

The software compiles without problem.  The first time it runs fine, the
second and subsequent times, it segfaults.  (If I run it under gdb, it
segafaults every second time only.)  Ion has a call to hid_interrupt_write
in the main function.  If I wrap this call in a function call in another
function, it doesn't crash, but frequently returns 21.  If I add unrelated
lines of code (like a new case in a switch statement that desn't do
anything!), it sometimes segfaults.

I stripped down the code to the point where it writes the command to the
HID and then fecthes any available bytes from the output HID, in a loop
every 0.5 seconds (20 times). I added calls to hid_set_debug and
hid_set_debug_stream.  In my stripped-down version, it seems that write
works the first time, reads work and then the second write fails and
subsequent reads fail. hid_close works.  My stripped-down version doens't
segfault (but doesn't do anything useful!)

My questions:

1)  How stable is the libhid code in SVN? (i.e. is it believed robust, or
highly experimental?)  No criticism implied ... I'm new around here and I
don't know.

2) Any suggestions as to why I might be seeing segfaults (in believed good
code)?

3) Any idea why me second write fails? What should I be doing differently?

Many Thanks!

Regards,
tom m.