Document d_poll() and d_select().
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Eivind Eklund
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svn2git
2020-12-08 03:00:23 +00:00
svn path=/head/; revision=2942
2 changed files with 190 additions and 4 deletions
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@ -6,7 +6,7 @@
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++
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++ Copyright Eric L. Hernes - Wednesday, August 2, 1995
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++
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++ $Id: ddwg.sgml,v 1.4 1997-10-03 20:53:38 wosch Exp $
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++ $Id: ddwg.sgml,v 1.5 1998-06-12 13:59:49 eivind Exp $
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++
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++ Sgml doc for something
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-->
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@ -153,7 +153,100 @@ is limited to one page (4k on the i386).
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<sect3> d_stop()
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<sect3> d_reset()
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<sect3> d_devtotty()
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<sect3> d_select()
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<sect3> d_poll() (3.0+) or d_select() (2.2)
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<p>
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d_poll()'s argument list is as follows:
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<code>
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void
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d_poll(dev_t dev, int events, struct proc *p)
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</code>
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<p> d_poll() is used to find out if a device is ready for IO. An
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example is waiting for data to become available from the network, or
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waiting for the user to press a key. This correspond to the poll()
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call in userland.
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<p>The d_poll() call should check for the events specified in the
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event mask. If none of the requested events are active, but they may
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become active later, it should record this for the kernel's later
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persual. d_poll() does this by calling selrecord() with a selinfo
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structure for this device. The sum of all these activities look
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something like this:
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<code>
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static struct my_softc {
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struct queue rx_queue; /* As example only - not required */
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struct queue tx_queue; /* As example only - not required */
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struct selinfo selp; /* Required */
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} my_softc[NMYDEV];
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...
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static int
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mydevpoll(dev_t dev, int events, struct proc *p)
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{
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int revents = 0; /* Events we found */
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int s;
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struct my_softc *sc = &my_softc[dev];
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/* We can only check for IN and OUT */
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if ((events & (POLLIN|POLLOUT)) == 0)
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return(POLLNVAL);
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s = splhigh();
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/* Writes are if the transmit queue can take them */
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if ((events & POLLOUT) &&
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!IF_QFULL(sc->tx_queue))
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revents |= POLLOUT;
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/* ... while reads are OK if we have any data */
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if ((events & POLLIN) &&
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!IF_QEMPTY(sc->rx_queue))
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revents |= POLLIN;
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if (revents == 0)
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selrecord(p, &sc->selp);
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splx(s);
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return revents;
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}
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</code>
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<p>
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d_select() is used in 2.2 and previous versions of FreeBSD. Instead
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of 'events' it take a single int 'rw', which can be FREAD for reads
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(as in POLLIN above), FWRITE for write (as in POLLOUT above), and 0
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for 'exception' - something exceptional happened, like a card being
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inserted or removed for the pccard driver.
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<p>For select, the above code fragment would look like this:
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<code>
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static int
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mydevselect(dev_t dev, int rw, struct proc *p)
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{
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int ret = 0;
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int s;
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struct my_softc *sc = &my_softc[dev];
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s = splhigh();
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switch (rw) {
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case FWRITE:
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/* Writes are if the transmit queue can take them */
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if (!IF_QFULL(sc->tx_queue))
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ret = 1;
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break;
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case FREAD:
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/* ... while reads are OK if we have any data */
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if (!IF_QEMPTY(sc->rx_queue))
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ret = 1;
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break;
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case 0:
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/* This driver never get any exceptions */
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break;
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if(ret == 0)
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selrecord(p, &sc->selp);
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splx(s);
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return(revents);
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}
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</code>
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<sect3> d_mmap()
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<sect3> d_strategy()
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<p>
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@ -6,7 +6,7 @@
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++
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++ Copyright Eric L. Hernes - Wednesday, August 2, 1995
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++
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++ $Id: ddwg.sgml,v 1.4 1997-10-03 20:53:38 wosch Exp $
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++ $Id: ddwg.sgml,v 1.5 1998-06-12 13:59:49 eivind Exp $
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++
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++ Sgml doc for something
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-->
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@ -153,7 +153,100 @@ is limited to one page (4k on the i386).
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<sect3> d_stop()
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<sect3> d_reset()
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<sect3> d_devtotty()
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<sect3> d_select()
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<sect3> d_poll() (3.0+) or d_select() (2.2)
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<p>
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d_poll()'s argument list is as follows:
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<code>
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void
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d_poll(dev_t dev, int events, struct proc *p)
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</code>
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<p> d_poll() is used to find out if a device is ready for IO. An
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example is waiting for data to become available from the network, or
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waiting for the user to press a key. This correspond to the poll()
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call in userland.
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<p>The d_poll() call should check for the events specified in the
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event mask. If none of the requested events are active, but they may
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become active later, it should record this for the kernel's later
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persual. d_poll() does this by calling selrecord() with a selinfo
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structure for this device. The sum of all these activities look
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something like this:
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<code>
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static struct my_softc {
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struct queue rx_queue; /* As example only - not required */
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struct queue tx_queue; /* As example only - not required */
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struct selinfo selp; /* Required */
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} my_softc[NMYDEV];
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...
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static int
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mydevpoll(dev_t dev, int events, struct proc *p)
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{
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int revents = 0; /* Events we found */
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int s;
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struct my_softc *sc = &my_softc[dev];
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/* We can only check for IN and OUT */
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if ((events & (POLLIN|POLLOUT)) == 0)
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return(POLLNVAL);
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s = splhigh();
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/* Writes are if the transmit queue can take them */
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if ((events & POLLOUT) &&
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!IF_QFULL(sc->tx_queue))
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revents |= POLLOUT;
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/* ... while reads are OK if we have any data */
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if ((events & POLLIN) &&
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!IF_QEMPTY(sc->rx_queue))
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revents |= POLLIN;
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if (revents == 0)
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selrecord(p, &sc->selp);
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splx(s);
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return revents;
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}
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</code>
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<p>
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d_select() is used in 2.2 and previous versions of FreeBSD. Instead
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of 'events' it take a single int 'rw', which can be FREAD for reads
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(as in POLLIN above), FWRITE for write (as in POLLOUT above), and 0
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for 'exception' - something exceptional happened, like a card being
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inserted or removed for the pccard driver.
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<p>For select, the above code fragment would look like this:
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<code>
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static int
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mydevselect(dev_t dev, int rw, struct proc *p)
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{
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int ret = 0;
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int s;
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struct my_softc *sc = &my_softc[dev];
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s = splhigh();
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switch (rw) {
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case FWRITE:
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/* Writes are if the transmit queue can take them */
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if (!IF_QFULL(sc->tx_queue))
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ret = 1;
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break;
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case FREAD:
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/* ... while reads are OK if we have any data */
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if (!IF_QEMPTY(sc->rx_queue))
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ret = 1;
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break;
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case 0:
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/* This driver never get any exceptions */
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break;
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if(ret == 0)
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selrecord(p, &sc->selp);
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splx(s);
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return(revents);
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}
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</code>
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<sect3> d_mmap()
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<sect3> d_strategy()
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<p>
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