Libguestfs - Feb 2023 - [PATCH] lib: Choose q35 machine type for x86-64

This machine type is more modern than the older 'pc' type and as most
qemu development is now focused there we expect it will perform and
behave better.  In almost all respects this change should make no
difference.

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=2168578
---
 lib/guestfs-internal.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/lib/guestfs-internal.h b/lib/guestfs-internal.h
index 07a2b9f617..4e9a103d78 100644
--- a/lib/guestfs-internal.h
+++ b/lib/guestfs-internal.h
@@ -128,6 +128,9 @@ cleanup_mutex_unlock (pthread_mutex_t **ptr)
 #define MAX_WINDOWS_EXPLORER_SIZE (4 * 1000 * 1000)
 
 /* Machine types. */
+#if defined(__x86_64__)
+#define MACHINE_TYPE "q35"
+#endif
 #ifdef __arm__
 #define MACHINE_TYPE "virt"
 #endif
-- 
2.39.0

On Thu, Feb 09, 2023 at 01:45:33PM +0000, Richard W.M. Jones
wrote:
> This machine type is more modern than the older 'pc' type and as
most
> qemu development is now focused there we expect it will perform and
> behave better.  In almost all respects this change should make no
> difference.
The key differences with q35 that have caused problems for
apps in the past

 - CDROMs must use 'sata' bus not 'ide'
 - PCI topology is completely different, so if you're
   trying to associate between the host side view of
   the config and the guest side view, your logic may
   need adapting
 - Hotplug of devices is limited to 1 device unless you
   pre-create a bunch of pcie-root-port devices

If you're already using 'virt' machine for aarch64 successfully
though, you should have already known about the last 2 points,
if they did indeed affect libguestfs.

The first point could conceivably affect the way to detect
devices, depending on what approach is used, but could equally
be a non issue.

I presume the libguestfs test suite would have complained if
there was any genuine problem with the change, since it is
pretty comphrensive.
> 
> Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=2168578
> ---
>  lib/guestfs-internal.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/lib/guestfs-internal.h b/lib/guestfs-internal.h
> index 07a2b9f617..4e9a103d78 100644
> --- a/lib/guestfs-internal.h
> +++ b/lib/guestfs-internal.h
> @@ -128,6 +128,9 @@ cleanup_mutex_unlock (pthread_mutex_t **ptr)
>  #define MAX_WINDOWS_EXPLORER_SIZE (4 * 1000 * 1000)
>  
>  /* Machine types. */
> +#if defined(__x86_64__)
> +#define MACHINE_TYPE "q35"
> +#endif
>  #ifdef __arm__
>  #define MACHINE_TYPE "virt"
>  #endif
> -- 
> 2.39.0
> 
> _______________________________________________
> Libguestfs mailing list
> Libguestfs at redhat.com
> https://listman.redhat.com/mailman/listinfo/libguestfs
> 
With regards,
Daniel
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