Month: November 2021

Convert Raspberry Pi Ubuntu to iSCSI btrfs root

Posted on by Bian Xi Leave a Comment on Convert Raspberry Pi Ubuntu to iSCSI btrfs root

Convert Raspberry Pi Ubuntu to iSCSI btrfs root

This is to move root file system of Raspberry Pi Ubuntu OS to iSCSI LUN and convert it to btrfs file system

Pros

  • Cheaper than using small SD card
  • Backup and restore easy, only need to backup 150MB boot partition on SD card
  • Able to perform snapshot at LUN level or OS level (btrfs)
  • Should be Faster

Steps

Install iscsi packages

apt install open-iscsi
systemctl enable open-iscsi
systemctl start open-iscsi
systemctl enable iscsid
systemctl start iscsid

Configure iscsi

Edit /etc/iscsi/initiatorname.iscsi, update following line

InitiatorName=<YOUR_INITIATOR_NAME>

Note: The YOUR_INITIATOR_NAME is the iSCSI client name

Edit /etc/iscsi/iscsid.conf, update following lines

node.session.auth.authmethod = CHAP
node.session.auth.username = <YOUR_USERNAME>
node.session.auth.password = <YOUR_PASSWORD>
# iscsiadm --mode discovery --type sendtargets --portal <YOUR_TARGET_IP>
# iscsiadm --mode node --targetname <YOUR_TARGET_NAME> --portal <YOUR_TARGET_IP> --login

Note: If can not login, restart iscsid and try again.

systemctl restart iscsid

Identify block device

Use lsblk command to identify device file, normally should be /dev/sda.

Partitioning

Creating two partitions using fdisk, the first partition is to prepare following for future used, such as

  • Network boot
  • UEFI iSCSI boot
  • SD card backup

Partition /dev/sda1: vfat, 2GB
Partition /dev/sda2: for root filesystem

Create filesystems

mkfs.vfat /dev/sda1
mkfs.btrfs /dev/sda2

Identify UUID for root filesystem

blkid /dev/sda2

Update initramfs

This is to enable ubuntu load iscsi driver during boot

touch /etc/iscsi/iscsi.initramfs
update-initramfs -v -k $(uname -r) -c

Duplicate files

mount /dev/sda2 /mnt
rsync -avhP --exclude /boot/firmware --exclude /proc --exclude /sys --exclude /dev --exclude /mnt / /mnt/
mkdir /mnt/{dev,proc,sys,boot/firmware,mnt}

Modify /etc/fstab in LUN

Note: Don't modify the file in /etc, it will not be used during iSCSI boot.

vi /mnt/etc/fstab

Change root mounting to

UUID=<YOUR_DEV_UUID> / btrfs defaults 1 1

Modify /boot/firmware/cmdline.txt

First create a backup of this file

cp /boot/firmware/cmdline.txt /boot/firmware/cmdline.txt.sav

Change the content of /boot/firmware/cmdline.txt

Note: Beware of rootfstype=btrfs

net.ifnames=0 dwc_otg.lpm_enable=0 console=serial0,115200 console=tty1 rootfstype=btrfs elevator=deadline rootwait fixrtc ip=dhcp root=UUID=<YOUR_DEV_UUID> ISCSI_INITIATOR=<YOUR_INITIATOR_NAME> ISCSI_TARGET_NAME=<YOUR_TARGET_NAME> ISCSI_TARGET_IP=<YOUR_TARGET_IP> ISCSI_TARGET_PORT=3260 ISCSI_USERNAME=<YOUR_USERNAME> ISCSI_PASSWORD=<YOUR_PASSWORD> rw

Note: Root partition can also be identified by label if assigned one, see next topic

Reboot

umount /mnt
reboot

Use LABEL for root

Using label instead of UUID for root filesystem.

Assign a label

For mounted filesystem

sudo btrfs filesystem label <mountpoint> <newlabel>

For not mounted filesystem

sudo btrfs filesystem label <device> <newlabel>

Change /etc/fstab

LABEL=<newlabel> / btrfs defaults 1 1

Change /boot/fireware/cmdline.txt

... root=LABEL=<newlabel> ...

Use Static IP

To use static IP for iSCSI connection, the ip definition in cmdline.txt needs to be changed to

ip=192.168.1.200::192.168.1.1:255.255.255.0:rpi:eth0:off

This will create an IP 192.168.1.200 on interface eth0 as below.

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    link/ether dc:a6:32:ef:07:0f brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.200/24 brd 192.168.1.255 scope global eth0
       valid_lft forever preferred_lft forever
    inet 192.168.1.23/24 brd 192.168.1.255 scope global secondary dynamic eth0
       valid_lft 43036sec preferred_lft 43036sec
    inet6 fe80::dea6:32ff:feef:70f/64 scope link
       valid_lft forever preferred_lft forever

One way to just maintain one IP is, disabling OS IP address.

Reboot

Other cmdline.txt format

I tried following format, but failed. I think it maybe work if no partition in iSCSI LUN

root=iscsi:[<username>:<password>[:<reverse>:<password>]@][<servername>]:[<protocol>]:[<port>][:[<iscsi_iface_name>]:[<netdev_name>]]:[<LUN>]:<targetname>

Use UUID is better, because there is no need to worry about LUN id and partition as UUID is unique ideitifier.

To specfic UUID, following format can be used according to kernel parameters, but it doesn't work too.

root=UUID=<UUID>
netroot=iscsi:[<username>:<password>[:<reverse>:<password>]@][<servername>]:[<protocol>]:[<port>][:[<iscsi_iface_name>]:[<netdev_name>]]:[<LUN>]:<targetname>

I also tried rd.* format, such as rd.iscsi.initiator, etc., they are new format to replace old format ISCSI_INITIATOR, etc., but also not failed. I think the dracut.cmdline version used by ubuntu in raspberry pi is old. Maybe should try grub2 used in Fedora OS for raspberry pi, or uefi used in Windows 10.

Backup and restore using pre-backup data

Backup data into iSCSI LUN partition 1

First create vfat in iSCSI LUN as partition 1, then backup /boot/fireware data into that partition

mkfs.vfat /dev/sda1
mount /dev/sda1 /mnt
cp /boot/firmware/. /mnt
umount /mnt

Restore to an empty SD card

Create partition in new SSD as type c, which W95 FAT32 (LBA), with Boot flag.

Device         Boot Start     End Sectors  Size Id Type
/dev/mmcblk0p1       2048 1050623 1048576  512M  c W95 FAT32 (LBA)

Format SD card and give label as system-boot, the LABEL is defined in /etc/fstab, it can be changed to UUID if needed.

mkfs.vfat -n system-boot /dev/sdb1
mount /dev/sdb1 /mnt
cp -a <backup_filesystem> /mnt
umount /mnt

Make sure system reported correct LABEL on the newly created vfat filesystem, using blkid command to verify.

Troubleshooting

iscsi_tcp missing

If following error occurred, install package linux-modules-extra.

libkmod: ERROR ../libkmod/libkmod-module.c:838 kmod_module_insert_module: could not find module by name='iscsi_tcp'

Please read post Missing iSCSI module in Ubuntu 20.10

Reboot error

If failed to boot, initram command prompt will appear. In this case, following commands can be used to recover back the booting.

mkdir /mnt
mount /dev/mmcblk0p1 /mnt
cd /mnt
cp cmdline.txt.sav cmdline.txt
cd /
umount /mnt
reboot

Note: the umount is very important, otherwise, the changes wouldn't be saved.

There are very minimum commands can be used, such as no vi. So let it boots into previous status, then troubleshooting from there.

References

dracut kernel command line options
Kernel command line parameters
introduction to boot time parameters of the Linux kernel
Raspberry Pi 4 UEFI Boot
RPi cmdline.txt
RPi config.txt
kernel-parameters.txt
The config.txt file
Raspberry Pi iSCSI Root on Ubuntu 20.04
btrfs root filesystem on raspbian
[Howto] booting from iSCSI
Ubuntu Server 20.10 on Raspberry Pi 4: installation guide with USB Boot (no SD card) and full disk encryption (excluding /boot) using btrfs-inside-luks and auto-apt snapshots with Timeshift
Raspberry Pi 4 - Ubuntu 20.04 w/Btrfs root
dracut.cmdline(7) — Linux manual page

Bcache Basic

Posted on by Bian Xi Leave a Comment on Bcache Basic

Bcache Basic

Update

After finished first round of writing, I think it needs to be described in clearer way.

During first time setup, I got very confused by the document I was using, and didn't understand fully. After observation of the devices behavior, I think I will review this document later.

Install

apt install bcache-tools

Concept

Bcache adds in one more layer between the actual filesystem and the block device (partition, raid, etc.) which filesystem located in. This is done by relocating filesystem header behind bcache header in block device, which offset the ordinary filesystem header and data 8KiB behind.

Note: Use partition as example

Ordinary filesystem partition = (Ordinary filesystem header + Ordinary filesystem data)
bcache partition = bcache header (8KiB) + (Ordinary filesystem header + Ordinary filesystem data)
                                          -------------------------------------------------------
                                                                  bcache data

In such case, the device (partition) is represented as a bcache partition, and bcache driver creates a new device called /dev/bcacheX without bcache header, then OS will detect /dev/bcacheX as ordinary filesystem.

This method is widely used in disk encryption as well, which allows encryption driver translates encrypted data device to OS in a newly created device.

Mount a filesystem bypass bcache header

By using following method, the ordinary filesystem in bcache partition can be mounted by ordinary filesystem driver without bcache driver.

  • Create Loopback Device
losetup -o 8192 /dev/loop0 /dev/[BCACHE DEVICE]
  • Mount Device
mount /dev/loop0 -o loop /mnt/[LOCATION]

Devices

Backing Device

Backing device is the actual device holding data, for example, /dev/sdb1, it can be 10TB hard disk, disk raid, software raid, etc. It can be created by following command

make-bcache -B /dev/sdb1

It will create a bcache device as well, such as /dev/bcache0

Bcache device

Bcache device is the device created together with backing device (/dev/sdb1), such as /dev/bcache0, all ordinary filesystem operation will be operated on bcache device (/dev/bcache0), such as mkfs, etc.

Caching Device

Caching device is the temporary device used as cache, for example /dev/sdc1, it can be 128GB SSD. It can be created using following command

make-bcache -C /dev/sdc1

It has cset.uuid as below

# bcache-super-show /dev/sdc1 | grep cset
cset.uuid       f0e01318-f4fd-4fab-abbb-d76d870503ec

Before recreate caching device, use following command clean up the device header.

wipefs -a /dev/<device>

Attach

Attach action allows caching device starts working for backing device.

# echo <caching_device_uuid> > /sys/block/<bcache_device>/bcache/attach
echo f0e01318-f4fd-4fab-abbb-d76d870503ec > /sys/block/bcache0/bcache/attach
# or to the backing device
echo f0e01318-f4fd-4fab-abbb-d76d870503ec > /sys/block/sdb/sdb1/bcache/attach

Note: If following error occurred, and no output when ran bcache-status command, then run partprobe command to rescan partition tables

# bcache-status
#
# echo f0e01318-f4fd-4fab-abbb-d76d870503ec > /sys/block/bcache0/bcache/attach
-bash: echo: write error: No such file or directory
# partprobe

*Note: bcache-status is a free bcache tool can be downloaded from github.

Operation on backing device and bcache device

The backing device and the bcache device have 1-to-1 relationship, because they are created at same time using one make-bcache -C command.

In fact, both bcache folders in both bcache and backing device are the same.

# ls -Hdi /sys/block/sdb/sdb1/bcache
64954 /sys/block/sdb/sdb1/bcache
# ls -Hdi /sys/block/bcache0/bcache
64954 /sys/block/bcache0/bcache

I think the correct thinking should be attaching to bcache device, but the bcache folder is created under backing device.

# readlink -f /sys/block/bcache0/bcache
/sys/devices/platform/host2/session1/target2:0:0/2:0:0:1/block/sdb/sdb1/bcache

I think this is because that bcache device is a virtual device created during backing device (real device) creation, so the actual device structure should assign to real device (backing device).

With or without caching device

Without caching device, bcache driver will directly translate ordinary filesystem driver read/write into bcache device read/write.

With cache device, bcache driver will utilize caching device before backing device operation.

ordinary filesystem operation => bcache driver => bcache filesystem operation => backing device
                                       ||
                                       ||
                                 caching device

So, without caching device, bcache is still operating correctly.

Attach caching device to multiple bcache devices

One caching device can support multiple bcache devices as below

# echo f0e01318-f4fd-4fab-abbb-d76d870503ec > /sys/block/bcache0/bcache/attach
# echo 4b05ce02-19f4-4cc6-8ca0-1f765671ceda > /sys/block/bcache1/bcache/attach
# echo 4b05ce02-19f4-4cc6-8ca0-1f765671ceda > /sys/block/bcache2/bcache/attach
# echo 4b05ce02-19f4-4cc6-8ca0-1f765671ceda > /sys/block/bcache3/bcache/attach
# echo 75ff0598-7624-46f6-bcac-c27a3cf1a09f > /sys/block/bcache4/bcache/attach

A bcache device has only one caching device

The uuid of caching device which attached to bcache device can be found as below.

# ls -la /sys/block/<device>/bcache/cache
lrwxrwxrwx 1 root root 0 Jun 19 18:42 /sys/block/<device>/bcache/set -> ../../../../../../../../fs/bcache/<UUID>

Detach

To detach a caching device, needs to send 1 or cache-set-uuid to bcache device or backing device

Safely remove the caching device from bcache device

echo cache-set-uuid > /sys/block/bcache0/bcache/detach
# or
echo cache-set-uuid > /sys/block/sdb/sdb1/bcache/detach

Detach the caching device from bcache device

echo 1 > /sys/block/bcache0/bcache/detach
# or
echo 1 > /sys/block/sdb/sdb1/bcache/detach

Stop

bcache/backing device

Stop a bcache device, is the same as stop the backing device.

echo 1 > /sys/block/bcache0/bcache/stop
# or
echo 1 > /sys/block/sdb/sdb1/bcache/stop

After stopped bcache/backing device,

  • The /sys/block/sdb/sdb1/bcache folder disappears
  • The /sys/block/bcache0 virtual device disappers
  • But no impact to caching device, and still registered in /sys/fs/bcache/<uuid>.

caching device

Stop caching device, will impact all caching, bcache and backing devices

echo 1 > /sys/fs/bcache/cache-set-uuid/stop

After stopped caching device, all bcache setup related to that caching device disapper

  • The /sys/block/sdb/sdb1/bcache folder disappers if /dev/sdb1 is backing device attached
  • The bcache devices /sys/block/bcache0 disappers if /dev/bcache0 is the bcache device attached
  • The caching device /sys/fs/bcache/<uuid> disappers

To resume

The first way to resume whole setup, can be done by run partprobe.

The second way is using register to resume device one by one.

Register

In fact, registering is needed every bootup, but attaching only have to be done once.

Register is required if the caching or backing device missing during system start up or they are stopped manually.

Register the backing device as below

echo /dev/sdb1 > /sys/fs/bcache/register     # backing device

After registered, the system will

  • Creates /sys/block/sdb/sdb1/bcache folder
  • If didn't attach caching device before stopped or caching device had been registered, then creates /sys/block/bcache0 virtual device

If /sys/block/bcache0 is not created due to missing caching device,

  • The /sys/block/bcache0 device will be created after register missing caching device
  • Or use following command to force to create /sys/block/bcache0 and start running
echo 1 > /sys/block/sdb/sdb1/bcache/running

Warning: If force start, all write cache in caching device will be lost, this can cause filesystem corruption

Register caching device

To register caching device, following command can be used

echo /dev/sdc1 > /sys/fs/bcache/register     # caching device

It will create directory /sys/fs/bcache/<uuid> folder.

If attached backing device had been registered, the /sys/block/bcache0 will be created and running.

Ordinary filesystem operation

All ordinary filesystem operations will be operated on bcache device (/dev/bcache0), for example

mkfs.btrfs /dev/bcache0
mount /dev/bcache0 /mnt
...

Caching state

The caching state can be viewed using following command

cat /sys/block/bcache0/bcache/state

Output:

  • no cache: this means you have not attached a caching device to your backing bcache device
  • clean: this means everything is ok. The cache is clean.
  • dirty: this means everything is setup fine and that you have enabled writeback and that the cache is dirty.
  • inconsistent: you are in trouble because the backing device is not in sync with the caching device

Caching mode

There are 4 caching modes, writethrough, writeback, writearound, and none.

echo writeback > /sys/block/bcache0/bcache/cache_mode

Show caching device info

bcache-super-show /dev/sdXY

Writeback Percent

echo 100 > /sys/block/bcache0/bcache/writeback_percent

Dirty data

How much data in cache has not written into backing device.

cat /sys/block/sda/sda3/bcache/dirty_data

Flush cache to backing device

This might be required if filesystem maintenance needed.

Run following command to disable writeback mode

echo writethrough > /sys/block/bcache0/bcache/cache_mode

Wait until state reports "clean"

watch cat /sys/block/bcache0/bcache/state

Force flush of cache to backing device

echo 0 > /sys/block/bcache0/bcache/writeback_percent

Errors

The /sys/fs/bcache/ folder does not exist

The bcache module was not loaded.

sh: echo: write error: Invalid argument

If dmesg shows

bcache: bch_cached_dev_attach() Couldn't attach sdc: block size less than set's block size

Then the --block 4k parameter was not set on either device and defaults can mismatch.

Otherwise, the device might already be attached.

sh: echo: write error: No such file or directory

The UUID is not a valid cache.

Other considerations

Boot from bcache device

Grub2 does not offer support for bcache, but it is fully supported by UEFI. Check the following link for details

https://wiki.archlinux.org/title/Bcache

References

Bcache
A block layer cache (bcache)
bcache-status

Xbox Series X|S Wireless Controller

Posted on by Bian Xi Leave a Comment on Xbox Series X|S Wireless Controller

Xbox Series X|S Wireless Controller

The Xbox Series X|S wireless controller works with Xbox One, Windows 10, and cloud gaming devices.

Layout

N Name N Name
1 Left stick 10 Expansion port
2 Left bumper 11 Right stick
3 View button 12 Left trigger
4 Xbox button 13 USB-C power port
5 Share button X X button
6 Menu button Y Y button
7 Right bumper A A button
8 Directional pad (D-pad) B B button
9 3.5-mm port

References

Get to know your Xbox Series X|S Wireless Controller

Btrfs Basic

Posted on by Bian Xi Leave a Comment on Btrfs Basic

Btrfs Basic

Status

btrfs device states /app
btrfs fi show /app

Convert raid

Convert to raid0 and remove one disk

btrfs balance start -f -sconvert=single -mconvert=single -dconvert=single /app
btrfs device remove /dev/bcache0 /app

Add disk and convert to raid1

btrfs device add -f /dev/bcache0 /app
btrfs balance start -dconvert=raid1 -mconvert=raid1 /app

Check raid level

# btrfs fi df /app
Data, RAID1: total=2.69GiB, used=2.51GiB
System, RAID1: total=32.00MiB, used=16.00KiB
Metadata, RAID1: total=317.94MiB, used=239.55MiB
GlobalReserve, single: total=12.03MiB, used=0.00B
#

If contains multiple block group profiles, could happen when a profile conversion using balance filters was interrupted.

Data, RAID1: total=2.03GiB, used=1.86GiB
Data, single: total=704.00MiB, used=665.56MiB
System, RAID1: total=32.00MiB, used=16.00KiB
Metadata, RAID1: total=288.00MiB, used=239.56MiB
GlobalReserve, single: total=11.94MiB, used=0.00B
WARNING: Multiple block group profiles detected, see 'man btrfs(5)'.
WARNING:   Data: single, raid1

Perform rebalance again

# btrfs balance start -dconvert=raid1 -mconvert=raid1 /app
Done, had to relocate 12 out of 12 chunks

Scrub

btrfs scrub start /app
btrfs scrub status /app

Error

To correct error, first find out corrupted file, then restore from backup or delete the file

dmesg -T | grep BTRFS | grep 'check error' | grep path

Then reset error count to zero

btrfs device states -z /app

Then scrub again.

References

BTRFS-MAN(5)

Show dd progress in MacOS

Posted on by Bian Xi Leave a Comment on Show dd progress in MacOS

Show dd progress in MacOS

The default dd command in MacOS doesn't have progress option.

Solution

Send SIGINFO signal to the dd command.

Press Control-T

By pressing the Control-T character in dd terminal, you are sending the same SIGINFO signal to the dd command.

Run kill command

Run following command in another Shell.

pkill -INFO -x dd

or

kill -INFO <pid>

References

How can I track progress of dd

Snap Basic

Posted on by Bian Xi Leave a Comment on Snap Basic

Snap Basic

To check the snap utility version, you need to use snap --version command as shown below.

Basic Commands

snap install <snap_name>
snap remove <snap_name>
snap remove <snap_name> --purge       # No snapshot generated
snap list
snap list --all
snap info <snap_name>
snap find <snap_name>
snap revert <snap_name>
snap enable <snap_name>
snap disable <snap_name>
snap download <snap_name>

Snap updates

snap refresh <snap_name>
snap refresh --list

Snap Channels (releases)

They are stable, edge, beta and candidate.

# snap install --edge <snap_name>
# snap install --beta <snap_name>
# snap install --candidate <snap_name>

Snap Changes

snap changes

Snap Connections

snap connections <snap_name>

Snap Model/Version

snap model
snap --version

Snap Service

snap services lxd
snap restart lxd
snap stop lxd
snap start lxd
snap logs lxd

Snap Alias

snap alias <snap_name> <alias_name>
snap aliases
snap unalias <alias_name>

Snap Snapshot

snap save
snap check-snapshot <snapshot_num>
snap restore <snapshot_num>
snap forget <snapshot_num>        # Delete a snapshot
snap saved
snap saved --id=<snapshot_num>        # View a snapshot

Snap login

snap login
snap logout

Snap Config

snap set system refresh.retain=2
snap get system refresh.retain
snap unset system refresh.retain

References

36 Popular Snap command examples in Linux for Beginners

Missing iSCSI module in Ubuntu 20.10

Posted on by Bian Xi Leave a Comment on Missing iSCSI module in Ubuntu 20.10

Missing iSCSI module in Ubuntu 20.10

Recently, I have upgraded Ubuntu 20.04 to 20.10, then iscsi_tcp module is missing, which caused iscsi LUN could not be loaded.

I checked /var/log/syslog, showed zram (reported by init-zram-swapping) and autofs (reported by containerd) module were missing too.

Error

Looking at error message shown during iscsi discovery, the command was looking for file iscsi_tcp.ko. Which can not be found in the system.

Update

The latest missing package can be installed using following command.

apt install linux-modules-extra-raspi

apt search

When performing apt search, shows three packages should include such file, but when listing all files in those packages, there is no iscsi_tcp.ko file at all.

# apt search iscsi_tcp.ko
Sorting... Done
Full Text Search... Done
libopeniscsiusr/impish,now 2.1.4-0ubuntu1 arm64 [installed]
  iSCSI userspace library

libopeniscsiusr-dev/impish 2.1.4-0ubuntu1 all
  iSCSI userspace library headers

open-iscsi/impish,now 2.1.4-0ubuntu1 arm64 [installed]
  iSCSI initiator tools

Reinstall OS

Then I decided to install a new fresh OS, but got the same result.

Search in ubuntu website

When searching packages content file iscsi_tcp.ko from ubuntu website, found there is no module package called linux-modules-extra for kernel 5.13.0-1009-raspi, the latest is 5.13.0-1008-raspi, which is for 20.04.

https://packages.ubuntu.com/search?suite=impish§ion=all&arch=any&keywords=iscsi_tcp.ko&searchon=contents

In other words, 20.10 doesn't have iscsi_tcp module, at all.

# apt install linux-modules-extra
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
E: Unable to locate package linux-modules-extra
#

Search in ubuntu repo

Then I go to ubuntu packages repo site below

http://ports.ubuntu.com/ubuntu-ports/pool/main/l/linux-raspi/

...
/lib/modules/5.13.0-1008-oracle/kernel/drivers/scsi/libiscsi_tcp.ko     linux-modules-5.13.0-1008-oracle [arm64, amd64]
/lib/modules/5.13.0-1008-raspi-nolpae/kernel/drivers/scsi/iscsi_tcp.ko  linux-modules-extra-5.13.0-1008-raspi-nolpae [armhf]
/lib/modules/5.13.0-1008-raspi-nolpae/kernel/drivers/scsi/libiscsi_tcp.ko   linux-modules-extra-5.13.0-1008-raspi-nolpae [armhf]
/lib/modules/5.13.0-1008-raspi/kernel/drivers/scsi/iscsi_tcp.ko     linux-modules-extra-5.13.0-1008-raspi [armhf, arm64]
/lib/modules/5.13.0-1008-raspi/kernel/drivers/scsi/libiscsi_tcp.ko  linux-modules-extra-5.13.0-1008-raspi [armhf, arm64]
/lib/modules/5.13.0-19-generic-64k/kernel/drivers/scsi/iscsi_tcp.ko     linux-modules-5.13.0-19-generic-64k [arm64] 
...

found that there are linux-modules-extra package for both 1009 and 1010.

...
[ ] linux-modules-5.13.0-1010-raspi_5.13.0-1010.11_armhf.deb    2021-10-29 10:29    23M
[ ] linux-modules-extra-5.13.0-1008-raspi-nolpae_5.13.0-1008.9_armhf.deb    2021-09-29 20:44    21M
[ ] linux-modules-extra-5.13.0-1008-raspi_5.13.0-1008.9_arm64.deb   2021-09-29 20:43    23M
[ ] linux-modules-extra-5.13.0-1008-raspi_5.13.0-1008.9_armhf.deb   2021-09-29 20:44    21M
[ ] linux-modules-extra-5.13.0-1009-raspi-nolpae_5.13.0-1009.10_armhf.deb   2021-10-28 08:33    21M
[ ] linux-modules-extra-5.13.0-1009-raspi_5.13.0-1009.10_arm64.deb  2021-10-28 08:33    23M
[ ] linux-modules-extra-5.13.0-1009-raspi_5.13.0-1009.10_armhf.deb  2021-10-28 08:33    21M
[ ] linux-modules-extra-5.13.0-1010-raspi-nolpae_5.13.0-1010.11_armhf.deb   2021-10-29 10:29    21M
[ ] linux-modules-extra-5.13.0-1010-raspi_5.13.0-1010.11_arm64.deb  2021-10-29 10:29    23M
[ ] linux-modules-extra-5.13.0-1010-raspi_5.13.0-1010.11_armhf.deb  2021-10-29 10:29    21M
[ ] linux-raspi-headers-5.4.0-1008_5.4.0-1008.8_arm64.deb   2020-04-10 11:18    11M
...

Install linux-modules-extra

Then I decided to do download the package and check the contents

wget http://ports.ubuntu.com/ubuntu-ports/pool/main/l/linux-raspi/linux-modules-extra-5.13.0-1009-raspi_5.13.0-1009.10_arm64.deb
dpkg -c linux-modules-extra-5.13.0-1009-raspi_5.13.0-1009.10_arm64.deb | grep iscsi

found the iscsi_tcp.ko is in the package

Install package via dpkg

dpkg -i linux-modules-extra-5.13.0-1009-raspi_5.13.0-1009.10_arm64.deb

Testing

Tested using iscsiadm, shows the problem fixed

iscsiadm --mode discovery --op update --type sendtargets --portal 192.168.1.17

In fact, this also fixed some other similar issues, such as, zram model missing, etc.

Reconfigure btrfs filesystem

In this system, the btrfs filesystem which was mirrored to iscsi LUN using bcache, the iscsi LUN was removed using following command during troubleshooting

btrfs balance start -f -sconvert=single -mconvert=single -dconvert=single /app
btrfs device remove /dev/bcache0 /app

Now use following command to reconfigure it back.

btrfs device add -f /dev/bcache0 /app
btrfs balance start -dconvert=raid1 -mconvert=raid1 /app

Configure module auto-loading

In order to load modules automatically, add iscsi_tcpline in /etc/modules. This may also avoid apt autoremove command removes linux-modules-extra package.

Possible cause

I think the issue was caused by spliting the kernel module package in to two in 1008, because linux-modules-extra only exists in the version 1008 in package searching list. I think ubnutu forgot this when releasing 1009. At this time, apt hasn't auto updated system to 1010.

References

Ubuntu Raspberry Package Repo
Ubuntu Package Searching
How to list files of a Debian package without install
How to install specific Ubuntu packages, with exact version?