[libvirt PATCH 2/2] qemu: preserve error on bandwidth rollback

[Ján Tomko <jtomko@xxxxxxxxxx>]

We call APIs that reset the error in the rollback code.
Preserve the error from the original call that failed.

This turns the boringly cryptic:
  error: Unable to set interface parameters
  error: An error occurred, but the cause is unknown
to the unexpectedly anarchist:
  error: internal error: Child process (/usr/sbin/tc filter add
  dev vnet1 parent ffff: protocol all u32 match u32 0 0 police
  rate 4294968kbps burst 4294968kb mtu 64kb drop flowid :1)
  unexpected exit status 1: Illegal "rate"
  Illegal "police"

Signed-off-by: Ján Tomko <jtomko@xxxxxxxxxx>
Fixes: f02e21cb3379a41cd42f2d8116f2d10dabace83b
https://bugzilla.redhat.com/show_bug.cgi?id=1800505
---
 src/qemu/qemu_driver.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 0324c771a5..ad5c7d9ff1 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -11661,6 +11661,9 @@ qemuDomainSetInterfaceParameters(virDomainPtr dom,
 
         if (virNetDevBandwidthSet(net->ifname, newBandwidth, false,
                                   !virDomainNetTypeSharesHostView(net)) < 0) {
+            virErrorPtr orig_err;
+
+            virErrorPreserveLast(&orig_err);
             ignore_value(virNetDevBandwidthSet(net->ifname,
                                                net->bandwidth,
                                                false,
@@ -11669,6 +11672,7 @@ qemuDomainSetInterfaceParameters(virDomainPtr dom,
                 ignore_value(virDomainNetBandwidthUpdate(net,
                                                          net->bandwidth));
             }
+            virErrorRestore(&orig_err);
             goto endjob;
         }
 
-- 
2.21.1