[libvirt] [PATCH 2/2 v2] storage: Add document for possible problem on volume detection

[John Ferlan]

On 01/22/2014 09:39 AM, Osier Yang wrote:
> For pool which relies on remote resources, such as a "iscsi" type
> pool, since how long it takes to export the corresponding devices
> to host's sysfs is really depended, it could depend on the network
> connection, it also could depend on the host's udev procedures. So
> it's likely that the volumes are not able to be detected during pool
> starting process, polling the sysfs doesn't work, since we don't
> know how much time is best for the polling, and even worse, the
> volumes could still be not detected or partly not detected even after
> the polling.  So we end up with a documentation to prompt the fact,
> in virsh manual.

Probably some of the above is overkill since the virsh.pod repeats much
of it - although having the intro comment specifically target udev
procedures (or "udevadm settle") as the culprit are good.  Also see my
change to your text below.

> 
> And as a small improvement, let's explicitly say no LUNs found in
> the debug log in that case.
> ---
>  src/storage/storage_backend_scsi.c | 5 +++++
>  tools/virsh.pod                    | 8 ++++++++
>  2 files changed, 13 insertions(+)
> 
> diff --git a/src/storage/storage_backend_scsi.c b/src/storage/storage_backend_scsi.c
> index 93039c1..fbcb102 100644
> --- a/src/storage/storage_backend_scsi.c
> +++ b/src/storage/storage_backend_scsi.c
> @@ -495,6 +495,7 @@ virStorageBackendSCSIFindLUs(virStoragePoolObjPtr pool,
>      DIR *devicedir = NULL;
>      struct dirent *lun_dirent = NULL;
>      char devicepattern[64];
> +    bool found = false;
>  
>      VIR_DEBUG("Discovering LUs on host %u", scanhost);
>  
> @@ -516,11 +517,15 @@ virStorageBackendSCSIFindLUs(virStoragePoolObjPtr pool,
>              continue;
>          }
>  
> +        found = true;
>          VIR_DEBUG("Found LU '%s'", lun_dirent->d_name);
>  
>          processLU(pool, scanhost, bus, target, lun);
>      }
>  
> +    if (!found)
> +        VIR_DEBUG("No LU found for pool %s", pool->def->name);
> +
>      closedir(devicedir);
>  
>      return retval;
> diff --git a/tools/virsh.pod b/tools/virsh.pod
> index 77f9383..073465e 100644
> --- a/tools/virsh.pod
> +++ b/tools/virsh.pod
> @@ -2650,6 +2650,14 @@ Refresh the list of volumes contained in I<pool>.
>  
>  Start the storage I<pool>, which is previously defined but inactive.
>  
> +B<Note>: For pool which relies on remote resources, e.g. a "iscsi" type
> +pool, or a "scsi" type pool based on a (v)HBA, since the corresponding
> +devices for the volumes may not show up on the host's sysfs yet during
> +the pool starting process, it may need to refresh the pool (see
> +B<pool-refresh>) to get the volumes correctly detected. How many times
> +needed for the refreshing is depended on the network connection and the
> +time the host takes to export the corresponding devices to sysfs.
> +
>  =item B<pool-undefine> I<pool-or-uuid>
>  
>  Undefine the configuration for an inactive I<pool>.
> 


B<Note>: A storage pool that relies on remote resources such as an
"iscsi" or a vHBA backed "scsi" pool may need to be refreshed multiple
times in order to have all the volumes detected (see B<pool-refresh>).
This is because the corresponding volume devices may not be present in
the host's filesystem during the initial pool startup or the current
refresh attempt. The number of refresh retries is dependant upon the
network connection and the time the host takes to export the
corresponding devices.


(sic) note that formatstorage.html.in has both vHBA and (v)HBA, while
virsh.pod presently only uses vHBA.  Whatever the *correct* syntax is
for the instance being used is what we should use here.

ACK with the change

John