[systemd-devel] How to stop systemd-udevd reading a device after dd

[Akira Hayakawa]

I've investigate myself what uevent are sent after each command.
I use "udevadm monitor" to watch the event sent from kernel.

The experiment starts from removing the existing device but
if it's placed at last, the uevents are the same.

What's very curious to me is that the ACTION!="remove" in my rule
only ignores the uevent from dd but the rest effects.
The uevent after dmsetup resume is considered even though the
uevent shapes the same as dd.

All I want to do is suppress the read after these commands.
I think it's health check by reading randomly chosen blocks.
I've observed that more than 100 of 4KB reads are submitted to my
logical device after creation and that hinders my tests as they
expect these extra IOs aren't existing. (more precisely saying
it's not black box test but white box that uses the internal stats
in assertions)

# dmsetup remove
KERNEL[4202.177671] remove   /devices/virtual/block/dm-0 (block)
KERNEL[4202.205822] remove   /kernel/slab/dmwb_buf_8 (slab)
KERNEL[4202.206786] remove   /kernel/slab/bio-3 (slab)
KERNEL[4202.250279] remove   /devices/virtual/bdi/251:0 (bdi)
KERNEL[4202.250776] remove   /devices/virtual/block/dm-0 (block)

# dmsetup create
KERNEL[4226.692607] add      /devices/virtual/bdi/251:0 (bdi)
KERNEL[4226.692852] add      /devices/virtual/block/dm-0 (block)
KERNEL[4226.695092] add      /kernel/slab/dmwb_buf_8 (slab)
KERNEL[4229.107766] add      /kernel/slab/bio-3 (slab)

# dd (write)
KERNEL[4229.108196] change   /devices/virtual/block/dm-0 (block)

# dmsetup suspend
# dmsetup resume
KERNEL[4271.409068] change   /devices/virtual/block/dm-0 (block)

- Akira