181 lines
2.7 KiB
HTML
181 lines
2.7 KiB
HTML
<HTML
|
|
><HEAD
|
|
><TITLE
|
|
>poll()</TITLE
|
|
><META
|
|
NAME="GENERATOR"
|
|
CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+
|
|
"><LINK
|
|
REL="HOME"
|
|
TITLE="The Linux SCSI Generic (sg) HOWTO"
|
|
HREF="index.html"><LINK
|
|
REL="UP"
|
|
TITLE="System calls"
|
|
HREF="syscalls.html"><LINK
|
|
REL="PREVIOUS"
|
|
TITLE="read()"
|
|
HREF="read.html"><LINK
|
|
REL="NEXT"
|
|
TITLE="close()"
|
|
HREF="close.html"></HEAD
|
|
><BODY
|
|
CLASS="SECT1"
|
|
BGCOLOR="#FFFFFF"
|
|
TEXT="#000000"
|
|
LINK="#0000FF"
|
|
VLINK="#840084"
|
|
ALINK="#0000FF"
|
|
><DIV
|
|
CLASS="NAVHEADER"
|
|
><TABLE
|
|
SUMMARY="Header navigation table"
|
|
WIDTH="100%"
|
|
BORDER="0"
|
|
CELLPADDING="0"
|
|
CELLSPACING="0"
|
|
><TR
|
|
><TH
|
|
COLSPAN="3"
|
|
ALIGN="center"
|
|
>The Linux SCSI Generic (sg) HOWTO</TH
|
|
></TR
|
|
><TR
|
|
><TD
|
|
WIDTH="10%"
|
|
ALIGN="left"
|
|
VALIGN="bottom"
|
|
><A
|
|
HREF="read.html"
|
|
ACCESSKEY="P"
|
|
>Prev</A
|
|
></TD
|
|
><TD
|
|
WIDTH="80%"
|
|
ALIGN="center"
|
|
VALIGN="bottom"
|
|
>Chapter 7. System calls</TD
|
|
><TD
|
|
WIDTH="10%"
|
|
ALIGN="right"
|
|
VALIGN="bottom"
|
|
><A
|
|
HREF="close.html"
|
|
ACCESSKEY="N"
|
|
>Next</A
|
|
></TD
|
|
></TR
|
|
></TABLE
|
|
><HR
|
|
ALIGN="LEFT"
|
|
WIDTH="100%"></DIV
|
|
><DIV
|
|
CLASS="SECT1"
|
|
><H1
|
|
CLASS="SECT1"
|
|
><A
|
|
NAME="POLL">7.4. poll()</H1
|
|
><DIV
|
|
CLASS="FORMALPARA"
|
|
><P
|
|
><B
|
|
>poll(struct pollfd *ufds, unsigned int nfds,
|
|
int timeout). </B
|
|
>This call can be used to check the state of a sg file descriptor. It
|
|
will always respond immediately. Typical usages are to periodically
|
|
poll the state of a sg file descriptor and to determine why a SIG_IO
|
|
signal was received.</P
|
|
></DIV
|
|
><P
|
|
>For file descriptors associated with sg devices:
|
|
<P
|
|
></P
|
|
><UL
|
|
><LI
|
|
><P
|
|
> POLLIN one or more responses is awaiting a read()</P
|
|
></LI
|
|
><LI
|
|
><P
|
|
> POLLOUT command can be sent to write() without causing an EDOM
|
|
error (i.e. sufficient space on sg's queues)</P
|
|
></LI
|
|
><LI
|
|
><P
|
|
> POLLHUP SCSI device has been detached, awaiting cleanup</P
|
|
></LI
|
|
><LI
|
|
><P
|
|
> POLLERR internal structures are inconsistent</P
|
|
></LI
|
|
></UL
|
|
></P
|
|
><P
|
|
>POLLOUT indicates the sg will not block a new write() or SG_IO ioctl().
|
|
However it is still possible (but unlikely) that the mid level or an
|
|
adapter may block (or yield EAGAIN).</P
|
|
></DIV
|
|
><DIV
|
|
CLASS="NAVFOOTER"
|
|
><HR
|
|
ALIGN="LEFT"
|
|
WIDTH="100%"><TABLE
|
|
SUMMARY="Footer navigation table"
|
|
WIDTH="100%"
|
|
BORDER="0"
|
|
CELLPADDING="0"
|
|
CELLSPACING="0"
|
|
><TR
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="left"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="read.html"
|
|
ACCESSKEY="P"
|
|
>Prev</A
|
|
></TD
|
|
><TD
|
|
WIDTH="34%"
|
|
ALIGN="center"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="index.html"
|
|
ACCESSKEY="H"
|
|
>Home</A
|
|
></TD
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="right"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="close.html"
|
|
ACCESSKEY="N"
|
|
>Next</A
|
|
></TD
|
|
></TR
|
|
><TR
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="left"
|
|
VALIGN="top"
|
|
>read()</TD
|
|
><TD
|
|
WIDTH="34%"
|
|
ALIGN="center"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="syscalls.html"
|
|
ACCESSKEY="U"
|
|
>Up</A
|
|
></TD
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="right"
|
|
VALIGN="top"
|
|
>close()</TD
|
|
></TR
|
|
></TABLE
|
|
></DIV
|
|
></BODY
|
|
></HTML
|
|
> |