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HAL-DISABLE-POLLING(1)	    General Commands Manual	HAL-DISABLE-POLLING(1)

NAME
       hal-disable-polling - disable polling on	drives with removable media

SYNOPSIS
       hal-disable-polling [options]

DESCRIPTION
       hal-disable-polling  can	 be used to to disable and enable media	detec-
       tion on drives with removable storage. For more information about  both
       the  big	 picture  and  specific	 HAL properties, refer to the HAL spec
       which can be found in  /usr/local/share/doc/hal/spec/hal-spec.html  de-
       pending on the distribution.

OPTIONS
       The following options are supported:

       --udi  The UDI (Unique Device Identifier) of the	device object.

       --device
	      The device file of the drive.

       --enable-polling
	      Enable polling instead of	disabling it.

       --help Print out	usage.

       --version
	      Print the	version.

NOTES
       This program requires super user	privileges.

RETURN VALUE
       If  the requested operation was successful, this	program	will exit with
       exit code 0.

HISTORY
       Polling a storage drive is a necessary evil to detect when the user in-
       serts  or  removes media. Human computer	interaction studies have shown
       that a broad class of users expect their	system to react	within	a  few
       seconds	of  this.  Thus, the hald daemon polls through the hald-addon-
       storage addon (one instance for each drive with removable media).

       The purpose of the hald-addon-storage addon is simply to	open the  spe-
       cial device file	at a regular interval (either every 2 or every 16 sec-
       onds) to	check for new media. This program tries	 to  open  the	device
       file using the O_EXCL option which means	that programs like cdrecord(1)
       that uses O_EXCL	automatically prevents the hald-addon-storage for  in-
       terferring  by continously opening the device file. In addition,	if the
       drive is	locked using  HAL  (see	 hal-lock(1))  the  addon  also	 stops
       polling.

       Unfortunately, polling a	storage	drive can have adverse side effects if
       the hardware and/or device driver for the hardware  is  malfunctioning.
       Additionally, the operating system kernel itself	may offer multiple in-
       terfaces	for the	same device (e.g.  /dev/sg0  and  /dev/scd0)  so  even
       O_EXCL  won't  work.  Also,  polling a drive may	decrease throughput in
       certain (odd and/or broken) configurations; for	example,  if  two  IDE
       drives  shares the same host (master/slave), bus	traffic	and contention
       caused by polling e.g. the optical drive	(slave)	can reduce  throughput
       to  the	hard disk (master) and/or interfere with CD burning on another
       optical drive (master). Finally,	polling	a  drive  incurs  an  overhead
       both  in	 the host system (processes get	woken up often,	preventing the
       CPU to stay in a	deep power saving states) and it may prevent  the  ac-
       tual  drive  from reaching deep power states as well. As	a result, more
       power is	consumed and this affects battery life for laptops.

       Despite the existence of	support	for asynchronous media change  notifi-
       cation  in  recent MMC (Multi-Media Commands) specifications, virtually
       no optical drives are compliant	with  the  specification.  Fortunately
       newer  SATA  ATAPI  hardware seems to support Asynchronous Notification
       (AN) and	at this	time of	writing	(March 2007) work is underway to  make
       both the	Linux operating	system kernel and HAL take advantage of	this.

       It  is  the  position of	the HAL	team that polling should be avoided at
       all costs as long as it doesn't heavily impact the user experience in a
       negative	 way.  This tool is provided as	a stop-gap measure to use if a
       system is rendered useless due to bugs in drivers and/or	hardware  that
       is  provoked  by	HAL polling the	drive. If such a bug is	encountered it
       should be reported (see the BUGS	section	below) so it can  be  fixed  -
       historically  hald  have	 triggered  a  number of bugs in Linux storage
       drivers and related subsystems (such  as	 USB)  that  have  later  been
       fixed.

BUGS
       Please  send  bug reports to either the distribution or the HAL mailing
       list, see http://lists.freedesktop.org/mailman/listinfo/hal on  how  to
       subscribe.

SEE ALSO
       hald(8),	lshal(1), hal-lock(1), open(2),	http://www.t10.org/scsi-3.htm,
       https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=halpolling

AUTHOR
       Written by David	Zeuthen	<david@fubar.dk> with a	lot of help from  many
       others.

							HAL-DISABLE-POLLING(1)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | NOTES | RETURN VALUE | HISTORY | BUGS | SEE ALSO | AUTHOR

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