I am not sure but I had understanded that we need to implement the pool syscall, as described in ldd3 books, only for chardevices. For attributes in sysfs, the poll syscall is managed by the kernel/sysfs and we can simply use sysfs_notify on the kernel side. An event queue is managed for each attribute for this purprose. But as I say before I am not clear with this. You can read this : http://lists.linuxcoding.com/kernel/2006-q1/msg28166.html or this from the kernel source: /* Sysfs attribute files are pollable. The idea is that you read * the content and then you use 'poll' or 'select' to wait for * the content to change. When the content changes (assuming the * manager for the kobject supports notification), poll will * return POLLERR|POLLPRI, and select will return the fd whether * it is waiting for read, write, or exceptions. * Once poll/select indicates that the value has changed, you * need to close and re-open the file, as simply seeking and reading * again will not get new data, or reset the state of 'poll'. * Reminder: this only works for attributes which actively support * it, and it is not possible to test an attribute from userspace * to see if it supports poll (Nether 'poll' or 'select' return * an appropriate error code). When in doubt, set a suitable timeout value. */ --- En date de : Mer 7.1.09, Belisko Marek <marek.belisko@xxxxxxxxx> a écrit : > De: Belisko Marek <marek.belisko@xxxxxxxxx> > Objet: Re: sysfs_notify & poll > À: "PAtrick Gerber" <kpa_info@xxxxxxxx> > Cc: kernelnewbies@xxxxxxxxxxxx > Date: Mercredi 7 Janvier 2009, 15h09 > Hi, > > On Wed, Jan 7, 2009 at 2:21 PM, PAtrick Gerber > <kpa_info@xxxxxxxx> wrote: > > Thanks for the information. > > > > I have tested with the example from > http://linux.die.net/man/3/poll slightly modified (see the > attached file). > > If I test pool on the > "/sys/module/systest/sections/.data" file it seems > to work fine. But if I try the same test application with my > attribute (/sys/kernel/kobject_example/bar) created with the > example from linux sources > (samples/kobject/kobject_example.c) the result is an event > POLLERR. > > > > > Do you have any idea why ? Need I to add special code > for support poll syscall in my driver ? > Of course you should implement poll syscall in kernel > driver. But for > kobject-example it could be a problem > because you don't have a file operations in this > example. But thats > only my feeling ;) > Example for poll : (ldd3 > http://lwn.net/images/pdf/LDD3/ch06.pdf ) > > > > Thanks in advance > > > > --- En date de : Mer 7.1.09, Belisko Marek > <marek.belisko@xxxxxxxxx> a écrit : > > > >> De: Belisko Marek <marek.belisko@xxxxxxxxx> > >> Objet: Re: sysfs_notify & poll > >> À: "PAtrick Gerber" > <kpa_info@xxxxxxxx> > >> Date: Mercredi 7 Janvier 2009, 13h59 > >> Hi, > >> > >> On Wed, Jan 7, 2009 at 1:54 PM, PAtrick Gerber > >> <kpa_info@xxxxxxxx> wrote: > >> > Ok thanks. Usefull example. But I have > another > >> question: > >> > > >> > Need I to use poll or epoll ? I dont really > understand > >> the difference. > >> epoll is a variant of poll that can be used either > as Edge > >> or Level > >> Triggered interface and scales well to large > numbers of > >> watched fds. > >> For beginnig you can use normal poll syscall. > >> > >> > > >> > Thanks in advance for any help ! > >> > > >> > On Wed, Jan 7, 2009 at 9:40 AM, PAtrick > Gerber > >> <kpa_info@xxxxxxxx> wrote: > >> >> Hello, > >> >> > >> >> I would like to try to use sysfs_notify() > / poll() > >> mechanism from my > >> > driver > >> >> to notify some events to my application. > I'm > >> looking for a tiny > >> > example > >> >> showing the use of this mechanism. > >> >> > >> >> The driver side with sysfs_notify seems > quite > >> simple but I have absolutely > >> >> no idea about the application side. > >> > > >> > Fo poll method you canfind good description > and also > >> example at: > >> > http://linux.die.net/man/3/poll > >> > > >> >> > >> >> Thanks in advance > >> >> > >> >> Patrick > >> >> > >> > > >> > thanks, > >> > > >> > Marek > >> > > >> > > >> > > >> > > >> > > >> > > >> > > >> > >> thanks, > >> > >> Marek > >> > >> -- > >> as simple as primitive as possible > >> ---------------------------------------------- > >> Marek Beliško - open-nandra > >> Ruská Nová Ves 219 > >> 08005 Prešov > >> Slovakia > >> http://open-nandra.com > > > > > > > > thanks, > > Marek > > -- > as simple as primitive as possible > ---------------------------------------------- > Marek Beliško - open-nandra > Ruská Nová Ves 219 > 08005 Prešov > Slovakia > http://open-nandra.com -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
