202 lines
3.4 KiB
HTML
202 lines
3.4 KiB
HTML
<HTML
|
|
><HEAD
|
|
><TITLE
|
|
>fcntl(sg_fd, F_SETFL, oflags | FASYNC)</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="mmap()"
|
|
HREF="mmap.html"><LINK
|
|
REL="NEXT"
|
|
TITLE="Errors reported in errno"
|
|
HREF="errors.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="mmap.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="errors.html"
|
|
ACCESSKEY="N"
|
|
>Next</A
|
|
></TD
|
|
></TR
|
|
></TABLE
|
|
><HR
|
|
ALIGN="LEFT"
|
|
WIDTH="100%"></DIV
|
|
><DIV
|
|
CLASS="SECT1"
|
|
><H1
|
|
CLASS="SECT1"
|
|
><A
|
|
NAME="FCNTL">7.7. fcntl(sg_fd, F_SETFL, oflags | FASYNC)</H1
|
|
><DIV
|
|
CLASS="FORMALPARA"
|
|
><P
|
|
><B
|
|
>fcntl(int sg_fd, int cmd, long arg). </B
|
|
>There are several uses for this system call in association with a sg
|
|
file descriptor. The following pseudo code shows code that is useful for
|
|
scanning the sg devices, taking care not to be caught in a wait for
|
|
an O_EXCL lock by another process, and when the appropriate device is
|
|
found, switching to normal blocked io. A working example of this logic
|
|
is in the sg_scan utility program.
|
|
<TABLE
|
|
BORDER="0"
|
|
BGCOLOR="#E0E0E0"
|
|
WIDTH="100%"
|
|
><TR
|
|
><TD
|
|
><FONT
|
|
COLOR="#000000"
|
|
><PRE
|
|
CLASS="PROGRAMLISTING"
|
|
>open("/dev/sg0", O_RDONLY | O_NONBLOCK)
|
|
/* check device, EBUSY means some other process has O_EXCL lock on it */
|
|
/* when the device you want is found then ... */
|
|
flags = fcntl(sg_fd, F_GETFL)
|
|
fcntl(sg_fd, F_SETFL, flags & (~ O_NONBLOCK))
|
|
/* since, with simple apps, it is easier to use normal blocked io */</PRE
|
|
></FONT
|
|
></TD
|
|
></TR
|
|
></TABLE
|
|
></P
|
|
></DIV
|
|
><P
|
|
>The sg driver supports asynchronous notification.
|
|
This is a non-blocking mode of operation in which, when the driver receives
|
|
data back from a device so that a read() can be done, it sends a SIGPOLL
|
|
(aka SIGIO) signal to the owning process. Here is a code snippet from
|
|
the sg_poll test program.
|
|
<TABLE
|
|
BORDER="0"
|
|
BGCOLOR="#E0E0E0"
|
|
WIDTH="100%"
|
|
><TR
|
|
><TD
|
|
><FONT
|
|
COLOR="#000000"
|
|
><PRE
|
|
CLASS="PROGRAMLISTING"
|
|
>sigemptyset(&sig_set)
|
|
sigaddset(&sig_set, SIGPOLL)
|
|
sigaction(SIGPOLL, &s_action, 0)
|
|
fcntl(sg_fd, F_SETOWN, getpid())
|
|
flags = fcntl(sg_fd, F_GETFL);
|
|
fcntl(sg_fd, F_SETFL, flags | O_ASYNC)</PRE
|
|
></FONT
|
|
></TD
|
|
></TR
|
|
></TABLE
|
|
></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="mmap.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="errors.html"
|
|
ACCESSKEY="N"
|
|
>Next</A
|
|
></TD
|
|
></TR
|
|
><TR
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="left"
|
|
VALIGN="top"
|
|
>mmap()</TD
|
|
><TD
|
|
WIDTH="34%"
|
|
ALIGN="center"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="syscalls.html"
|
|
ACCESSKEY="U"
|
|
>Up</A
|
|
></TD
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="right"
|
|
VALIGN="top"
|
|
>Errors reported in errno</TD
|
|
></TR
|
|
></TABLE
|
|
></DIV
|
|
></BODY
|
|
></HTML
|
|
> |