> directory notification capability in lk 2.4 (see
> Documentation/dnotify.txt) could then be used to detect
> changes in the /dev directory (or below).
Why ? Devfs will call devfsd on its own.
> A user mode notification daemon could read /proc/scsi/scsi
> periodically to detect the arrival and departure of SCSI
No ! This must not be done. Parsing /proc/scsi/scsi or for that matter
any other file in /proc by a user space demon is a race condition.
There's nothing you can do to change that. There's no way you could guarantee
that the information gained by parsing is still valid when you use it.
The coordination of a new device to a major/minor (or name) must be made in
kernel space and cannot be broken until the user mode helper returns.
Either devfs is used to do that or new event types are added to the
/sbin/hotplug mechanism. For SCSI you'd need it in the bus scanning code
and in the partition recognition code. As this is a larger undertaking, this
would indicate IMHO that it'd be wiser to use the infrastructure contained in
devfs. But there are other possibilities, however it must be done in kernel
space.
Regards
Oliver
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