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HAL-DISABLE-POLLING(1)                                  HAL-DISABLE-POLLING(1)

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

       hal-disable-polling [options]

       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/share/doc/packages/hal/spec/hal-spec.html
       depending on the distribution.

       The following options are supported:

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

              The device file of the drive.

              Enable polling instead of disabling it.

       --help Print out usage.

              Print the version.

       This program requires super user privileges.

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

       Polling a storage drive is a necessary evil to  detect  when  the  user
       inserts 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
       interferring  by  continously  opening the device file. In addition, if
       the drive is locked using HAL (see hal-lock(1)) the  addon  also  stops

       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
       interfaces 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
       actual 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

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

       hald(8), lshal(1), hal-lock(1), open(2), http://www.t10.org/scsi-3.htm,

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


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Gedruckt am: 15.12.2017 18:33 GMT+0100 (2017-12-15T18:33:50+01:00)