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Old 12-29-2012
Linux Rw-rw-rw
Pleas I want answer to this question ?

In UNIX, each device is represented by a device, give an example of a file representing the hard disk storage device. Give the full listing of this file using the "ls -l" command. What are the protection flags (rwx) for this file and WHY are they like this? What would happen if the protection flags were equal to rw-rw-rw ?
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LEARN ABOUT DEBIAN

bus_child_present

BUS_CHILD_PRESENT(9)					   BSD Kernel Developer's Manual				      BUS_CHILD_PRESENT(9)

NAME

     bus_child_present -- ask the bus driver to see if this device is still really present

SYNOPSIS

     #include <sys/param.h>
     #include <sys/bus.h>

     #include <machine/bus.h>
     #include <sys/rman.h>
     #include <machine/resource.h>

     int
     bus_child_present(device_t dev);

DESCRIPTION

     The bus_child_present() function requests that the parent device driver of dev check to see if the hardware represented by dev is still phys-
     ically accessible at this time.  While the notion of accessible varies from bus to bus, generally hardware that is not accessible cannot be
     accessed via the bus_space*() methods that would otherwise be used to access the device.

     This does not ask the question ``does this device have children?'' which can better be answered by device_get_children(9).

RETURN VALUES

     A zero return value indicates that the device is not present in the system.  A non-zero return value indicates that the device is present in
     the system, or that the state of the device cannot be determined.

EXAMPLES

     This is some example code.  It only calls stop when the dc(4) device is actually present.

	   device_t dev;
	   dc_softc *sc;

	   sc = device_get_softc(dev);
	   if (bus_child_present(dev))
		   dc_stop(sc);

SEE ALSO

     device(9), driver(9)

AUTHORS

     This manual page was written by Warner Losh <imp@FreeBSD.org>.

BSD
								  March 27, 2003							       BSD