[Bug 1887143] [NEW] mdmonitor closes mdstat fd if is empty

[Mariusz Tkaczyk]

Public bug reported:

There was a change in mdadm to fix issue when md_mod is reloaded (not a case for ubuntu because md_mod is build-in). Commit:
https://git.kernel.org/pub/scm/utils/mdadm/mdadm.git/commit/?id=52209d6ee1183581e148791cf6ee4d60a0193b1d

The fix prevents mdmonitor from occupying mdstat file descriptor in there is no any mddevice available.
As a side effect mdmonitor cannot react on md events because it is waiting in undefined resource (probably 1 which in demonize mode case is /dev/null).

When mdmonitor is started form command line and there was one mdmonitor
already active, error message also is omitted, because error is thrown
after forking. As a result, unexpectedly we may got same same issue
after array creation.

** Affects: mdadm (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1887143

Title:
  mdmonitor closes mdstat fd if is empty

Status in mdadm package in Ubuntu:
  New

Bug description:
  There was a change in mdadm to fix issue when md_mod is reloaded (not a case for ubuntu because md_mod is build-in). Commit:
  https://git.kernel.org/pub/scm/utils/mdadm/mdadm.git/commit/?id=52209d6ee1183581e148791cf6ee4d60a0193b1d

  The fix prevents mdmonitor from occupying mdstat file descriptor in there is no any mddevice available.
  As a side effect mdmonitor cannot react on md events because it is waiting in undefined resource (probably 1 which in demonize mode case is /dev/null).

  When mdmonitor is started form command line and there was one
  mdmonitor already active, error message also is omitted, because error
  is thrown after forking. As a result, unexpectedly we may got same
  same issue after array creation.

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