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Published 20 hours ago • verified publisher icon koverstreet

Add bcache-export-cached helper to export CACHED_UUID and CACHED_LABEL

Open raharper opened this issue 7 years ago • 5 comments

Linux kernel bcache driver does not always emit a uevent[1] for when a backing device is bound to a bcacheN device. When this happens, the udev rule for creating /dev/bcache/by-uuid or /dev/bcache/by-label symlinks does not fire and removes any persistent symlink to a specific backing device since the bcache minor numbers (bcache0, 1, 2) are not guaranteed across reboots[2][3].

This script reads the superblock of the bcache device slaves, ensuring the slave is a backing device via sb.version check, extracts the dev.uuid and dev.label values and exports them to udev for triggering the symlink rules in the existing rules file.

  1. https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1729145
  2. https://bugs.launchpad.net/bcache-tools/+bug/1728742
  3. https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=890446

raharper avatar Feb 15 '18 14:02 raharper

Can we just fix the kernel to always emit the uevent? Has that been looked at?

On Feb 15, 2018 09:48, "Ryan Harper" [email protected] wrote:

Linux kernel bcache driver does not always emit a uevent[1] for when a backing device is bound to a bcacheN device. When this happens, the udev rule for creating /dev/bcache/by-uuid or /dev/bcache/by-label symlinks does not fire and removes any persistent symlink to a specific backing device since the bcache minor numbers (bcache0, 1, 2) are not guaranteed across reboots[2][3].

This script reads the superblock of the bcache device slaves, ensuring the slave is a backing device via sb.version check, extracts the dev.uuid and dev.label values and exports them to udev for triggering the symlink rules in the existing rules file.

  1. https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1729145
  2. https://bugs.launchpad.net/bcache-tools/+bug/1728742
  3. https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=890446

You can view, comment on, or merge this pull request online at:

https://github.com/koverstreet/bcache-tools/pull/1 Commit Summary

  • Add bcache-export-cached helper to export CACHED_UUID and CACHED_LABEL always

File Changes

Patch Links:

  • https://github.com/koverstreet/bcache-tools/pull/1.patch
  • https://github.com/koverstreet/bcache-tools/pull/1.diff

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koverstreet avatar Feb 15 '18 16:02 koverstreet

On Thu, Feb 15, 2018 at 10:09 AM, koverstreet [email protected] wrote:

Can we just fix the kernel to always emit the uevent? Has that been looked at?

Yes, we have.

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1729145

Specifically: https://launchpadlibrarian.net/348212191/0001-bcache-decouple-emitting-a-cached_dev-CHANGE-uevent.patch

It may, or may not make it back to much older kernels were bcache is in use; so similar to working around blkid versions which didn't detect bcache, it's still useful to have a user-space solution.

On Feb 15, 2018 09:48, "Ryan Harper" [email protected] wrote:

Linux kernel bcache driver does not always emit a uevent[1] for when a backing device is bound to a bcacheN device. When this happens, the udev rule for creating /dev/bcache/by-uuid or /dev/bcache/by-label symlinks does not fire and removes any persistent symlink to a specific backing device since the bcache minor numbers (bcache0, 1, 2) are not guaranteed across reboots[2][3].

This script reads the superblock of the bcache device slaves, ensuring the slave is a backing device via sb.version check, extracts the dev.uuid and dev.label values and exports them to udev for triggering the symlink rules in the existing rules file.

  1. https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1729145
  2. https://bugs.launchpad.net/bcache-tools/+bug/1728742
  3. https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=890446

You can view, comment on, or merge this pull request online at:

https://github.com/koverstreet/bcache-tools/pull/1 Commit Summary

  • Add bcache-export-cached helper to export CACHED_UUID and CACHED_LABEL always

File Changes

Patch Links:

  • https://github.com/koverstreet/bcache-tools/pull/1.patch
  • https://github.com/koverstreet/bcache-tools/pull/1.diff

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raharper avatar Feb 15 '18 16:02 raharper

For the record, here are the upstream kernel submission discussions:

  • https://patchwork.kernel.org/patch/10252315/
  • https://lkml.org/lkml/2018/3/1/812
  • https://www.spinics.net/lists/linux-bcache/msg05833.html

basak avatar Mar 27 '18 18:03 basak

Please close this PULL REQUEST as it is outdated. Latest version is in:

https://github.com/koverstreet/bcache-tools/pull/6

rafaeldtinoco avatar Jul 22 '20 20:07 rafaeldtinoco

@raharper I amended your patch with the PATH change and will go from there. Keeping credits and all, just so you dont have to worry about following this closer. Doing the Debian & Ubuntu inner work now.

rafaeldtinoco avatar Jul 22 '20 20:07 rafaeldtinoco