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.\"
.\" hal-disable-polling manual page.
.\" Copyright (C) 2007 David Zeuthen <david@fubar.dk>
.\"
.TH HAL-DISABLE-POLLING 1
.SH NAME
hal-disable-polling \- disable polling on drives with removable media
.SH SYNOPSIS
.PP
.B hal-disable-polling
[options]
.SH DESCRIPTION
\fIhal-disable-polling\fP can be used to to disable and enable media
detection on drives with removable storage. For more information about
both the big picture and specific
.B HAL
properties, refer to the \fIHAL spec\fP which can be found in
.I "@docdir@/spec/hal-spec.html"
depending on the distribution.
.SH OPTIONS
The following options are supported:
.TP
.I "--udi"
The UDI (\fIUnique Device Identifier\fP) of the device object.
.TP
.I "--device"
The device file of the drive.
.TP
.I "--enable-polling"
Enable polling instead of disabling it.
.TP
.I "--help"
Print out usage.
.TP
.I "--version"
Print the version.
.SH NOTES
.PP
This program requires super user privileges.
.SH RETURN VALUE
.PP
If the requested operation was successful, this program will exit with
exit code 0.
.SH HISTORY
.PP
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
.I hald
daemon polls through the
.I hald-addon-storage
addon (one instance for each drive with removable media).
The purpose of the
.I hald-addon-storage
addon is simply to open the special device file at a regular interval
(either every 2 or every 16 seconds) to check for new media. This
program tries to open the device file using the
.B O_EXCL
option which means that programs like \&\fIcdrecord\fR\|(1) that uses
.B O_EXCL
automatically prevents the
.I hald-addon-storage
for interferring by continously opening the device file. In addition,
if the drive is locked using HAL (see \&\fIhal-lock\fR\|(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 interfaces for the same device (e.g. \&\fI/dev/sg0\fR\|
and \&\fI/dev/scd0\fR\|) so even
.B 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
notification 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
.I Linux
operating system kernel and
.I HAL
take advantage of this.
It is the position of the
.I 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
.B BUGS
section below) so it can be fixed - historically
.B hald
have triggered a number of bugs in
.I Linux
storage drivers and related subsystems (such as USB) that have later
been fixed.
.SH BUGS
.PP
Please send bug reports to either the distribution or the HAL
mailing list, see
.I "http://lists.freedesktop.org/mailman/listinfo/hal"
on how to subscribe.
.SH SEE ALSO
.PP
\&\fIhald\fR\|(8),
\&\fIlshal\fR\|(1),
\&\fIhal-lock\fR\|(1),
\&\fIopen\fR\|(2),
\&\fIhttp://www.t10.org/scsi-3.htm\fR\|,
\&\fIhttps://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=halpolling\fR\|
.SH AUTHOR
Written by David Zeuthen <david@fubar.dk> with a lot of help from many
others.
|
