[Bug 1913284] Re: [plugin] [bcache] add a new bcache plugin

[Eric Desrochers]

** Summary changed:

- [SRU] [plugin] [bcache] add a new bcache plugin
+ [plugin] [bcache] add a new bcache plugin

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https://bugs.launchpad.net/bugs/1913284

Title:
  [plugin] [bcache] add a new bcache plugin

Status in sosreport package in Ubuntu:
  Fix Released
Status in sosreport source package in Bionic:
  In Progress
Status in sosreport source package in Focal:
  In Progress
Status in sosreport source package in Groovy:
  In Progress
Status in sosreport source package in Hirsute:
  Fix Released

Bug description:
  [Impact]

  Gather bcache stats as part of sos report.

  Bcache is often deployed as a "frontend" (typically using SSDs) for
  Ceph cluster's with HDDs to improve performance. When we are dealing
  with bcache performance or need to debug bcache, these stats are
  essential to identify the problem. The newly added plugin collects
  various stats on bcache.

  
  [Test Case]

  It's a new plugin. When sosreport is run on a system with bcache, a
  number of small files from /sys/fs/bcache and /sys/block/bcache should
  be collected with this plugin in place. On systems, without bcache,
  this should be a no-op.

  
  [Where problems could occur]

  Worst case scenarios could be:
  - As with any plugin, this plugin, in theory, could potentially run indefinitely and timeout.
  - Affect performance when run on a live system. There's one known case where querying the proiorty_stats [0] had such a problem. But it's not collected as part of this plugin.

  But otherwise, the stats collection of bcache devices (even if there
  are many bcache devices deployed on a system) shouldn't affect
  anything on a live system and shouldn't get anywhere closer to
  timeout.

  
  [Other Info]
   
  upstream PR (merged): https://github.com/sosreport/sos/pull/2384


  [0] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1840043

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