Re: [naviserver-devel] Problem with a Tcl extension and NaviServer

[Matthew B. <mm...@gm...>]

Hi Gustaf,

Thanks for the reply. I'll start looking into permissions issues and see if
anything there looks promising. I should also instrument the USB library
and try to get a better sense of what, exactly, is failing.

Regards,

Matt


On Thu, Jun 27, 2024 at 9:15 AM <
nav...@li...> wrote:

>
> Dear Mathew,
>
> The answer for your this problem is probably in the call of
> blink1_openById(devid);
>
> Without looking into this call, I would suspect first from my experience
> with NaviServer IoT projects a permission problem when accessing the
> hardware interface.
> For security reasons, NaviServer switches to a nonprivileged user ...
>
> all the best -g
>
> On 25.06.24 16:18, Matthew Burke wrote:
> > Hello!
> >
> > I am writing a Tcl extension in C to wrap a driver for a USB LED
> > status light. The extension runs fine from tclsh but there are issues
> > running it from a Tcl ?page under NaviServer.
> >
> > The extension implements one command via Tcl_CreateObjCommand. The
> > command proc implements a number of sub-commands broken into two
> > categories: device-independent functionality, e.g. count the number of
> > status lights that are plugged in, and device-dependent functionality,
> > e.g. attach to a status light, display a particular color, etc
> >
> > The device-independent sub-commands work when run in a Tcl page. For
> > example, this page runs fine when served from NaviServer:
> >
> >
> > package require blink
> >
> > set n [blink enumerate]
> >
> > ns_return 200 text/html "
> > There are <strong>$n</strong> devices plugged in.
> > "
> >
> >
> > In order to have a device display a color, etc., you first have to run
> > the "open" command. And that's not working. So here's an example Tcl
> page:
> >
> >
> > package require blink
> >
> > set d [blink open 0]
> > set q [ns_conn query]
> > set s [ns_parsequery $q]
> >
> > set red [ns_set get $s red 255]
> > set green [ns_set get $s green 0]
> > set blue [ns_set get $s blue 0]
> >
> > blink set $d $red $green $blue
> >
> > ns_return 200 text/html "
> > ? ? <p>Query: [ns_conn query]</p>
> >
> > ? ? <ul>
> > ? ? <li>Red: $red</li>
> > ? ? <li>Green: $green</li>
> > ? ? <li>Blue: $blue</li>
> > ? ? </ul>
> > "
> >
> >
> > When this page is served, I get an error in the line: set d [blink
> > open 0].
> >
> > There is a C struct, Blinker, ?that contains data about the attached
> > device. My C code first allocates
> > memory for the struct
> >
> >
> > blinkPtr = (Blinker *)Tcl_Alloc(sizeof(Blinker));
> >
> >
> > and this seems to work -- blinkPtr is non-NULL after the assignment.
> > Then there is a function from the driver library that actually
> > attaches to the device:
> >
> > blinkPtr->device = blink1_openById(devid);
> >
> > It should return the memory address of an allocated structure that's
> > part of the USB library. But the?function?returns NULL. (Just to
> > reiterate, this works fine when run from tclsh and returns a non-NULL
> > value.)
> >
> > I'm assuming there is some sort of memory protection or similar that I
> > need to take into account. Any suggestions on what to look at would be
> > greatly appreciated.
> >
> > Thanks,
> >
> > Matt
> >
> > P.S. This is on macOS 14.3. I'm compiling the extension as follows:
> >
> > clang -dynamiclib -DUSE_TCL_STUBS -I/usr/local/ns/include
> > -L/usr/local/ns/lib -ltclstub8.6 -o blink.dylib blink.c
> > -L/usr/local/lib -lBlink1
> >
> >
> >
> >
> > _______________________________________________
> > naviserver-devel mailing list
> > nav...@li...
> > https://lists.sourceforge.net/lists/listinfo/naviserver-devel
>
>
>
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