[Bug 1611945] Re: /dev/disk/by-path not properly populated for (e)SATA port multiplier disks

[Norman Henderson]

Ladies and Gentlemen, The technical stuff is way over my head but I am
getting the same syslog errors and the same inconsistent device paths on
an HP Proliant ML110 G7 with Ubuntu 16.04.3 kernel 4.4.0-98-generic.

It seems clear that no-one is taking ownership of this to fix it in an
actual update that ordinary people like me can install in the normal
course of system updates. The nature of open source software I guess.

However could someone please let me know:
 - is this just an annoying message that won't be fixed, or are there operational implications?
 - if there are implications, are they serious?
 - if they are serious, could you explain (or point me at a resource that explains) in detail, how to install the patch provided. I've never done that before.

Thank you in advance!

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https://bugs.launchpad.net/bugs/1611945

Title:
  /dev/disk/by-path not properly populated for (e)SATA port multiplier
  disks

Status in systemd package in Ubuntu:
  Confirmed

Bug description:
  We have a just-installed Ubuntu 16.04 LTS machine with a number of
  disks behind port-multiplier eSATA ports, all of them driven by a SiI
  3124 controller (sata_sil24 kernel driver). Our machine sees all disks
  on all channels, however under 16.04 only one disk from each channel
  shows up in /dev/disk/by-path/ (all disks show up in /dev/disk/by-id
  and /dev/disk/by-uuid). For our usage this is a severe defect because
  we rotate disks in and out of the external enclosure and rely on
  mounting specific slots in the external enclosure through /dev/disk
  /by-path.

  This did not happen in Ubuntu 12.04 LTS, the release that this machine
  was previously running.

  According to 'udevadm info --export-db' and 'udevadm test-builtin
  path_id' and so on, systemd's udev stuff is assigning all drives
  behind the same port the same disk/by-path data (ID_PATH et al). In
  'udevadm info /sys/block/sdX', the 'P:' and 'E: DEVPATH=' values show
  a difference in the target portion of PCI path, eg:

    P: /devices/pci0000:00/0000:00:01.0/0000:01:00.0/0000:02:00.0/ata1/host0/target0:0:0/0:0:0:0/block/sda
    P: /devices/pci0000:00/0000:00:01.0/0000:01:00.0/0000:02:00.0/ata1/host0/target0:1:0/0:1:0:0/block/sdb

  However the 'S: disk/by-path', 'E: DEVLINKS=', and 'E: ID_PATH'
  portions do not. For both devices above, we see:

    S: disk/by-path/pci-0000:02:00.0-ata-1
    E: ID_PATH=pci-0000:02:00.0-ata-1

  Naturally only one device can have a /dev/disk/by-
  path/pci-0000:02:00.0-ata-1 symlink, so instead of four disks per
  channel in /dev/disk/by-path we see one.

  Ubuntu release: 16.04

  Package versions from 'apt-cache policy udev systemd':
  udev:
    Installed: 229-4ubuntu7
  systemd:
    Installed: 229-4ubuntu7

  'journalctl -b' reports that during boot systemd does report some
  'appeared twice with different sysfs paths' notes, eg:

  Aug 10 13:34:21 verdandi systemd[1]: dev-disk-by\x2dpath-
  pci\x2d0000:02:00.0\x2data\x2d1\x2dpart1.device: Dev dev-disk-by
  \x2dpath-pci\x2d0000:02:00.0\x2data\x2d1\x2dpart1.device appeared
  twice with different sysfs paths
  /sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0/0000:02:00.0/ata1/host0/target0:3:0/0:3:0:0/block/sdd/sdd1
  and
  /sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0/0000:02:00.0/ata1/host0/target0:0:0/0:0:0:0/block/sda/sda1

  However it doesn't seem to be reporting this for all port-multiplier
  drives and their partitions.

  If it would be useful I can attach full 'udevadm info --export-db'
  output or the like.

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