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Re: [libvirt] [PATCH 2/2] storage: Add thread to refresh for createVport



On 19.11.2014 21:52, John Ferlan wrote:
https://bugzilla.redhat.com/show_bug.cgi?id=1152382

When libvirt create's the vport (VPORT_CREATE) for the vHBA, there isn't
enough "time" between the creation and the running of the following
backend->refreshPool after a backend->startPool in order to find the LU's.
Population of LU's happens asynchronously when udevEventHandleCallback
discovers the "new" vHBA port.  Creation of the infrastructure by udev
is an iterative process creating and discovering actual storage devices and
adjusting the environment.

Because of the time it takes to discover and set things up, the backend
refreshPool call done after the startPool call will generally fail to
find any devices. This leaves the newly started pool appear empty when
querying via 'vol-list' after startup. The "workaround" has always been
to run pool-refresh after startup (or any time thereafter) in order to
find the LU's. Depending on how quickly run after startup, this too may
not find any LUs in the pool. Eventually though given enough time and
retries it will find something if LU's exist for the vHBA.

This patch adds a thread to be executed after the VPORT_CREATE which will
attempt to find the LU's without requiring the external run of refresh-pool.
It does this by waiting for 5 seconds and searching for the LU's. If any
are found, then the thread completes; otherwise, it will retry once more
in another 5 seconds.  If none are found in that second pass, the thread
gives up.

Things learned while investigating this... No need to try and fill the
pool too quickly or too many times. Over the course of creation, the udev
code may 'add', 'change', and 'delete' the same device. So if the refresh
code runs and finds something, it may display it only to have a subsequent
refresh appear to "lose" the device. The udev processing doesn't seem to
have a way to indicate that it's all done with the creation processing of a
newly found vHBA. Only the Lone Ranger has silver bullets to fix everything.

Signed-off-by: John Ferlan <jferlan redhat com>
---
  src/storage/storage_backend_scsi.c | 131 +++++++++++++++++++++++++++++++++----
  1 file changed, 120 insertions(+), 11 deletions(-)

ACK

Michal


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