This commit was manufactured by cvs2svn to create tag

[linux-2.6.git] / Documentation / filesystems / devfs / README

diff --git a/Documentation/filesystems/devfs/README b/Documentation/filesystems/devfs/README
index 54366ec..3ef8582 100644 (file)
--- a/Documentation/filesystems/devfs/README
+++ b/Documentation/filesystems/devfs/README
@@ -1349,6 +1349,47 @@ This will cause devfsd to create (and destroy) symbolic links which
 point to the kernel-supplied names.
 
 
+SCSI Host Probing Issues
+
+Devfs allows you to identify SCSI discs based in part on SCSI host
+numbers. If you have only one SCSI host (card) in your computer, then
+clearly it will be given host number 0. Life is not always that easy
+is you have multiple SCSI hosts. Unfortunately, it can sometimes be
+difficult to guess what the probing order of SCSI hosts is. You need
+to know the probe order before you can use device names. To make this
+easy, there is a kernel boot parameter called "scsihosts". This allows
+you to specify the probe order for different types of SCSI hosts. The
+syntax of this parameter is:
+
+scsihosts=<name_1>:<name_2>:<name_3>:...:<name_n>
+
+where <name_1>,<name_2>,...,<name_n> are the names
+of drivers used in the /proc filesystem. For example:
+
+    scsihosts=aha1542:ppa:aha1542::ncr53c7xx
+
+
+means that devices connected to
+
+- first aha1542 controller   - will be /dev/scsi/host0/bus#/target#/lun#
+- first parallel port ZIP    - will be /dev/scsi/host1/bus#/target#/lun#
+- second aha1542 controller  - will be /dev/scsi/host2/bus#/target#/lun#
+- first NCR53C7xx controller - will be /dev/scsi/host4/bus#/target#/lun#
+- any extra controller       - will be /dev/scsi/host5/bus#/target#/lun#,
+                                       /dev/scsi/host6/bus#/target#/lun#, etc
+- if any of above controllers will not be found - the reserved names will
+  not be used by any other device.
+- /dev/scsi/host3/bus#/target#/lun# names will never be used
+
+
+You can use ',' instead of ':' as the separator character if you
+wish. I have used the devfsd naming scheme
+here.
+
+Note that this scheme does not address the SCSI host order if you have
+multiple cards of the same type (such as NCR53c8xx). In this case you
+need to use the driver-specific boot parameters to control this.
+
 -----------------------------------------------------------------------------
 
 
@@ -1911,6 +1952,12 @@ explores the SCSI subsystem and how it interacts with devfs
 
 Douglas Gilbert has written another useful document at
 
+http://www.torque.net/scsi/scsihosts.html which
+discusses the scsihosts= boot option
+
+
+Douglas Gilbert has written yet another useful document at
+
 http://www.torque.net/scsi/SCSI-2.4-HOWTO/ which
 discusses the Linux SCSI subsystem in 2.4.