[libvirt] [PATCH] qemu: Do not overwrite existing messages in hotplug

[Eric Farman]

I tried to attach a SCSI LUN to two different guests, and forgot
to specify "shareable" in the hostdev XML.  Attaching the device
to the second guest failed, but the message was not helpful in
telling me what I was doing wrong:

  $ cat scsi_scratch_disk.xml
    <hostdev mode='subsystem' type='scsi'>
      <source>
        <adapter name='scsi_host3'/>
        <address bus='0' target='15' unit='1074151456'/>
      </source>
    </hostdev>

  $ virsh attach-device dasd_sles_d99c scsi_scratch_disk.xml
  Device attached successfully

  $ virsh attach-device dasd_fedora_0e1e scsi_scratch_disk.xml
  error: Failed to attach device from scsi_scratch_disk.xml
  error: internal error: Unable to prepare scsi hostdev: scsi_host3:0:15:1074151456

I eventually discovered my error, but thought it was weird that
Libvirt doesn't provide something more helpful in this case.
Looking over the code we had just gone through, I commented out
the "internal error" message, and got something more useful:

  $ virsh attach-device dasd_fedora_0e1e scsi_scratch_disk.xml
  error: Failed to attach device from scsi_scratch_disk.xml
  error: Requested operation is not valid: SCSI device 3:0:15:1074151456 is already in use by other domain(s) as 'non-shareable'

Seems that the virReportError issued for an internal error
overwrites one that might have already existed.  Rather than
remove them altogether (there may be error paths that don't
spit out a more helpful message), I thought maybe it'd be
best to check if one exists, and exit if one does.  If not,
the existing internal error messages are probably helpful.

Make this adjustment for both virtio-scsi and vhost-scsi
devices.

Signed-off-by: Eric Farman <farman at linux.vnet.ibm.com>
Reviewed-by: Bjoern Walk <bwalk at linux.vnet.ibm.com>
Reviewed-by: Boris Fiuczynski <fiuczy at linux.vnet.ibm.com>
---
 src/qemu/qemu_hotplug.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c
index 120bcdc..d421a77 100644
--- a/src/qemu/qemu_hotplug.c
+++ b/src/qemu/qemu_hotplug.c
@@ -2470,6 +2470,10 @@ qemuDomainAttachHostSCSIDevice(virConnectPtr conn,
     if (qemuHostdevPrepareSCSIDevices(driver, vm->def->name,
                                       &hostdev, 1)) {
         virDomainHostdevSubsysSCSIPtr scsisrc = &hostdev->source.subsys.u.scsi;
+
+        if (virGetLastError())
+            return -1;
+
         if (scsisrc->protocol == VIR_DOMAIN_HOSTDEV_SCSI_PROTOCOL_TYPE_ISCSI) {
             virDomainHostdevSubsysSCSIiSCSIPtr iscsisrc = &scsisrc->u.iscsi;
             virReportError(VIR_ERR_INTERNAL_ERROR,
@@ -2595,9 +2599,12 @@ qemuDomainAttachSCSIVHostDevice(virQEMUDriverPtr driver,
 
     if (qemuHostdevPrepareSCSIVHostDevices(driver, vm->def->name, &hostdev, 1) < 0) {
         virDomainHostdevSubsysSCSIVHostPtr hostsrc = &hostdev->source.subsys.u.scsi_host;
-        virReportError(VIR_ERR_INTERNAL_ERROR,
-                       _("Unable to prepare scsi_host hostdev: %s"),
-                       hostsrc->wwpn);
+
+        if (!virGetLastError()) {
+            virReportError(VIR_ERR_INTERNAL_ERROR,
+                           _("Unable to prepare scsi_host hostdev: %s"),
+                           hostsrc->wwpn);
+        }
         return -1;
     }
 
-- 
1.9.1