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@redhat.com>
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

On 2/7/20 8:54 AM, Ján Tomko wrote:
> 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"

Anarchy In The Libvirt!

> 
> Signed-off-by: Ján Tomko <jtomko@redhat.com>
> Fixes: f02e21cb3379a41cd42f2d8116f2d10dabace83b
> https://bugzilla.redhat.com/show_bug.cgi?id=1800505
> ---

Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>


>   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;
>           }
>   
>