removable media revalidation - udev vs. devfs or static /dev

Andrey Borzenkov
2004-01-01T20:42:10Z

udev names are created when kernel detects corr. device. Unfortunately for
removable media kernel rescans for partitions only when I try to access
device. Meaning - because kernel does not know partition table it did not
send hotplug event so udev did not create device nodes. But without device
nodes I have no way to access device in Unix :(

specifically I have now my Jaz and I have no (reasonable) way to access
partition 4 assuming device nodes are managed by udev.

devfs solved this problem by

- always exporting at least handle to the whole disk (sda as example)
- using something simple like dd if=/dev/sda count=1 on lookup for
non-existing partition (/dev/sda4) that would rescan partitions and create
device nodes for them.

static /dev simply has all nodes available and does not suffer from this
problem at all.

unfortunately there are no lookup events in case if udev ... meaning at this
moment user must manually rescan partitions after inserting new media. I do
not see any way to solve this problem at all given current implementation.
The closest is to blindly create nodes for all partitions as soon as block
device is available.

-andrey