[qubes-users] Setting block.no_part_scan=no on sys-usb’s command line does not work

Demi_M_Obenour · December 26, 2020, 2:13am

I am trying to disable automatic partition scanning in sys-usb,
and tried including block.no_part_scan=no in sys-usb’s kernelopts.
However, it had no effect. `block.no_part_scan=0` also doesn’t work.

Did I make a mistake in the command line?

Sincerely,

Demi

unman · December 26, 2020, 3:30am

no_part_scan=Y ?
test by writing to /sys/module/block/parameters/no_part_scan

rustybird · December 26, 2020, 9:47am

unman:

> I am trying to disable automatic partition scanning in sys-usb,
> and tried including block.no_part_scan=no in sys-usb’s kernelopts.
> However, it had no effect. `block.no_part_scan=0` also doesn’t work.

no_part_scan=Y ?
test by writing to /sys/module/block/parameters/no_part_scan

Yes it's Y, but with 'block.no_part_scan=Y' in kernelopts, the VM will
fail to boot because now it can't find /dev/xvda3 (root) or /dev/xvdc1
(swap). So this parameter is intended to be set by writing Y to /sys
after the VM has booted.

Block device content is also parsed by udev scans for filesystems etc.
In Split dm-crypt, those scans are disabled by installing a udev rules
file which piggybacks on the kernel parameter:

github.com

rustybird/qubes-split-dm-crypt/blob/master/vm/rules.d/00-blockdev-parsing-disabled.rules

IMPORT{db}="UDEV_DISABLE_PERSISTENT_STORAGE_RULES_FLAG"
IMPORT{db}="DM_NOSCAN"
IMPORT{db}="UDISKS_IGNORE"

ACTION=="add", SUBSYSTEM=="block", PROGRAM="/bin/cat /sys/module/block/parameters/no_part_scan", RESULT!="N", ENV{UDEV_DISABLE_PERSISTENT_STORAGE_RULES_FLAG}="1", ENV{DM_NOSCAN}="1", ENV{UDISKS_IGNORE}="1"

Rusty