Hi,
Apart from manually calling or running the script mentioned above, does
SLES automatically scan the PCI and SCSI buses at periodic intervals?
I’m trying to get an understanding of exactly what happens when device
disappears and reappears on the system.
I have my node attached by fiber to an EMC SAN (via a QLogic HBA with
qla2xxx driver). If I pull the fiber cables out, I can see udev entries
in /var/log/messages, telling me that the devices (sdb, sdc…) have
been removed. Similarly, if I put the fiber cables back in, I can see
udev entries in /var/log/messages, telling me that some devices have
been added. The problem I’m actually having is that they are appearing
with new (different) device names, so I’m trying to figure out how this
detection is working at a relatively low level in the kernel.
Could you please help me to understand exactly what initiates the
process that informs the kernel that the devices have been
removed/added?
Is the PCI or SCSI subsystem periodically scanning for changes on the
bus? My understanding (which may be incorrect) is that the PCI subsystem
scans for devices on the bus. When it finds one it will register the new
device with the device core and a kobject will be created in the kernel.
Then the list of drivers for the PCI (or SCSI) subsystem will be queried
until a matching driver for the new device is found. Then the driver
will initialize the new device and the reference counter in the device’s
associated kobject will be incremented, at which time a uevent will be
sent to udev.
Or, is it the driver that is responsible for detecting these changes
and informing the device core in the kernel?
I’d eventually like to understand why different names are assigned to
the devices when the cables are re-attached, but considering the topic
of this thread, I’d very much like to know what informs the kernel of
device status changes if the rescan-scsi-bus.sh script is not explicitly
being run by me.
Thanks and regards,
KK
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boy_named_suse
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