<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <meta name="Generator" content="Microsoft Word 15 (filtered medium)"> <style></style> </head> <body lang="EN-US" link="blue" vlink="purple"> <div class="WordSection1"> <p class="MsoNormal">Hi Mantas<o:p></o:p></p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">>>You really seem to be intent on using select() rather than an existing event loop or, at least, standard poll(); curious why.<o:p></o:p></p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">There is existing code blocking on select, so it seems like the easiest way to crowbar DBus into my code.<o:p></o:p></p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">>>Also, the 'sender' field is always a bus name (not sure but I think it's always the unique ":1.x" name), so "sender='testsignal'," would never match dbus-send (or anything at all).<o:p></o:p></p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">Is there a way to “match” against “:1.x” with sd-bus i.e. instead of “testsignal”? Is it advised to match against this, or should I have the emitting program request a name?<o:p></o:p></p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">Thanks,<o:p></o:p></p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">Brian<o:p></o:p></p> <p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p> <p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p> <p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> Mantas Mikulėnas [mailto:grawity@gmail.com] <br> <b>Sent:</b> Thursday, January 7, 2016 10:36 PM<br> <b>To:</b> Gorman, Brian (Vancouver)<br> <b>Cc:</b> systemd-devel@lists.freedesktop.org<br> <b>Subject:</b> Re: [systemd-devel] Multicast signaling with sd-bus questions<o:p></o:p></span></p> <p class="MsoNormal"><o:p> </o:p></p> <div> <div> <div> <p class="MsoNormal">On Fri, Jan 8, 2016 at 2:37 AM, Gorman, Brian (Vancouver) <<a href="mailto:bgorman@hp.com" target="_blank">bgorman@hp.com</a>> wrote:<o:p></o:p></p> <blockquote style="border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in"> <div> <div> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Hi all, I am in the process of considering using sd-bus to coordinate a system-wide multicast messaging system between daemons. At this time I only have resources to look into using libsystemd without system running. It seems the sd-bus documentation is very sparse compared to sd-event – does this mean sd-bus is more immature?<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">My initial goal is to be able to select() on dbus-signals. Unfortunately my dbus experience is quite minimal, and I am not sure what this will take. Here is my initial attempt adapted from Lennarts tutorial – I have no idea if this is the right approach I was hoping if this list could perhaps provide some guidance as I suspect I am doing a few things wrong.<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">int main(int argc, char *argv[]) {<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> sd_bus_slot *slot = NULL;<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> sd_bus *bus = NULL;<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> int r;<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> int fd;<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> fd_set rd_fdset;<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> int my_user_data;<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> /* Connect to the system bus this time */<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> r = sd_bus_open_system(&bus);<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> if (r < 0) {<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> fprintf(stderr, "Failed to connect to bus: %s\n", strerror(-r));<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> goto finish;<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> }<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> r = sd_bus_request_name(bus, "Test.Me", 0);<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> if (r < 0) {<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> fprintf(stderr, "Failed to acquire service name: %s\n", strerror(-r));<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> goto finish;<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> }<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> r = sd_bus_add_match(<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> bus,<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> slot,<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> "type='signal',"<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> "sender='testsignal',"<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> "interface='Japan.Reset',"<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> "member='Test',"<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> "path='/Japan'",<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> my_signal_callback,<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> my_user_data);<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> fd = sd_bus_get_fd(bus);<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> if (fd < 0)<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> assert(0);<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> FD_ZERO(&rd_fdset);<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> FD_SET(fd, &rd_fdset);<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> for (;;) {<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;text-indent:.5in"> select(fd +1, &rd_fdset, NULL, NULL,NULL);<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> r = sd_bus_process(bus, NULL);<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> if (r < 0) {<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> fprintf(stderr, "Failed to process bus: %s\n", strerror(-r));<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> goto finish;<o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> } <o:p></o:p></p> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> }<o:p></o:p></p> </div> </div> </blockquote> <div> <p class="MsoNormal"><o:p> </o:p></p> </div> <div> <p class="MsoNormal">You really seem to be intent on using select() rather than an existing event loop or, at least, standard poll(); curious why.<o:p></o:p></p> </div> <div> <p class="MsoNormal"> <o:p></o:p></p> </div> <blockquote style="border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in"> <div> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">From here I was hoping to run something like “dbus-send –system –dest=Test.Me –print-reply /Japan Japan.Reset.Test string:”Hello””<o:p></o:p></p> </div> </blockquote> <div> <p class="MsoNormal"><o:p> </o:p></p> </div> <div> <p class="MsoNormal">You're sending a method call here, not a signal. (And signals wouldn't have a reply to --print; that's the main difference from methods.) Try `dbus-send --type=signal` or `gdbus emit`.<o:p></o:p></p> </div> <div> <p class="MsoNormal"><o:p> </o:p></p> </div> <div> <p class="MsoNormal">Also, the 'sender' field is always a bus name (not sure but I think it's always the unique ":1.x" name), so "sender='testsignal'," would never match dbus-send (or anything at all).<o:p></o:p></p> </div> <div> <p class="MsoNormal"><o:p> </o:p></p> </div> <blockquote style="border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in"> <div> <div> <p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">It currently get errors about DBUs complaining that Test.Me was not provided in any .service files when executing the above command.<o:p></o:p></p> </div> </div> </blockquote> <div> <p class="MsoNormal"><o:p> </o:p></p> </div> <div> <p class="MsoNormal">It says that because there's no connection who has claimed the "Test.Me" bus name, so dbus-daemon is trying to auto-start the apropriate daemon. On the system bus, AFAIK, the default policy only allows whitelisted names to be claimed, and usually only by root.<o:p></o:p></p> </div> <div> <p class="MsoNormal"><o:p> </o:p></p> </div> <div> <p class="MsoNormal">See the various dbus-daemon config drop-ins at /etc/dbus-1/system.d/, for example. (Many of them also try to whitelist the available method calls at dbus-daemon level, although that's not required – some services check credentials manually or use polkit.)<o:p></o:p></p> </div> <div> <p class="MsoNormal"><o:p> </o:p></p> </div> <div> <p class="MsoNormal">For development & debugging, you could use the session bus, which has no such restrictions.<o:p></o:p></p> </div> <div> <p class="MsoNormal"><o:p> </o:p></p> </div> <div> <p class="MsoNormal">(That said, I'm not sure why sd_bus_request_name would have succeeded in that case?)<o:p></o:p></p> </div> </div> <div> <p class="MsoNormal"><o:p> </o:p></p> </div> <p class="MsoNormal">-- <o:p></o:p></p> <div> <div> <p class="MsoNormal">Mantas Mikulėnas <<a href="mailto:grawity@gmail.com" target="_blank">grawity@gmail.com</a>><o:p></o:p></p> </div> </div> </div> </div> </div> </body> </html>