Re: Pseudo-device driver & select ??

From: Aziz Kezzou (french.linuxian_at_gmail.com)
Date: 05/27/05

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To: dave baukus <dbaukus@chiaro.com>, freebsd-hackers <freebsd-hackers@freebsd.org>, freebsd-net <freebsd-net@freebsd.org>

    > >
    > > Aziz Kezzou wrote:
    > > > Hi all,
    > > > I am trying to implement a small kld pseudo-device driver on FreeBSD 5.3 that
    > > > behaves just like a socket with regards to the select system call.
    > > >
    > > > Currently, I am using the sample echo pseudo-device driver from
    > > > http://www.freebsd.org/doc/en_US.ISO8859-1/books/arch-handbook/driverbasics-char.html
    > > > as an example. However, whenever I call select on the file
    > > > descriptor of "/dev/echo" it always returns even when there is no data
    > > > to be read.
    > > >
    > > > I looked at the socket code and it looks like I need to provide my own
    > > > "fo_select" function in the fileops data structure. Am i right ? How
    > > > do I do that ? The sample echo pseudo-device driver above uses
    > > > "struct cdevsw" instead...
    > > >
    > > > Thanks
    > > > -aziz
    > > > _______________________________________________
    > > > freebsd-net@freebsd.org mailing list
    > > > http://lists.freebsd.org/mailman/listinfo/freebsd-net
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    > > >
    > > >
    > > look at spec_poll()
    > > I beleive that when your device is opened the fileops{} will
    > > point to the spec ops and you're code will be entered via
    > > spec_poll() - now you just need to implement the poll/select notion
    > > for your device.
    > >
    >
    > Thanks,
    > Actually, il turned out to be very simple.
    > I needed only to provide a "d_poll" function as part of the structure
    > cdevsw, as follows :
    >
    > /* Character device entry points */
    > static struct cdevsw echo_cdevsw = {
    > .d_version = D_VERSION,
    > .d_open = echo_open,
    > .d_close = echo_close,
    > .d_read = echo_read,
    > .d_write = echo_write,
    > .d_poll = echo_poll,
    > .d_name = "echo",
    > };
    >
    > with echo_poll :
    > static int
    > echo_poll(struct cdev *dev, int events, struct thread *td)
    > {
    >
    > uprintf( "echo_poll called : data_available = %d!\n", data_available );
    > if(data_available == 0)
    > return 0;
    > data_available = 0;
    > return 1;
    > }
    >

    Now the question is, if I don't have any data available when select
    (i.e d_poll ) is called, how do I notify select when data arrives ?
    looks like "d_poll" is called only once (the name is a bit misleading
    here ;-) , isn't it ?

    Any hints ?
    Thanks.
    -aziz
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