On Tue, Apr 30, 2024 at 10:55:38AM +0100, Daniel P. Berrangé wrote: > On Tue, Apr 30, 2024 at 08:45:29AM +0200, Thomas Huth wrote: > > Old machine types often have bugs or work-arounds that affect our > > possibilities to move forward with the QEMU code base (see for example > > https://gitlab.com/qemu-project/qemu/-/issues/2213 for a bug that likely > > cannot be fixed without breaking live migration with old machine types, > > or https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg04516.html or > > commit ea985d235b86). So instead of going through the process of manually > > deprecating old machine types again and again, let's rather add an entry > > that can stay, which declares that machine types older than 6 years are > > considered as deprecated automatically. Six years should be sufficient to > > support the release cycles of most Linux distributions. > > Reading this again, I think we're mixing two concepts here. > > With this 6 year cut off, we're declaring the actual *removal* date, > not the deprecation date. > > A deprecation is something that happens prior to removal normally, > to give people a warning of /future/ removal, as a suggestion > that they stop using it. > > If we never set the 'deprecation_reason' on a machine type, then > unless someone reads this doc, they'll never realize they are on > a deprecated machine. > > When it comes to machine types, I see deprecation as a way to tell > people they should not deploy a /new/ VM on a machine type, only > use it for back compat (incoming migration / restore from saved > image) with existing deployed VMs. > > If we delete a machine on the 6 year anniversary, then users > don't want to be deploying /new/ VMs using that on the > 5 year anniversary as it only gives a 1 year upgrade window. > > So how long far back do we consider it reasonable for a user > to deploy a /new/ VM on an old machine type ? 1 year, 2 years, > 3 years ? > > > How about picking the half way point ? 3 years ? > > ie, set deprecation_reason for any machine that is 3 years > old, but declare that our deprecation cycle lasts for > 3 years, instead of the normal 1 year, when applied to > machine types. > > This would give a strong hint that users should get off the > old machine type, several years before its finally deleted. The m68k/arm archs have a nice macro for defining versions that exposes major/minor directly. That would let us automatically set the deprecation flag after 3 years, avoiding manually writing patches for each release: diff --git a/hw/arm/virt.c b/hw/arm/virt.c index 3c93c0c0a6..e40209f60a 100644 --- a/hw/arm/virt.c +++ b/hw/arm/virt.c @@ -101,6 +101,11 @@ static void arm_virt_compat_set(MachineClass *mc) arm_virt_compat_len); } +#define MACHINE_IS_DEPRECATED(major, minor) \ + ((QEMU_VERSION_MAJOR - major) > 3 || \ + ((QEMU_VERSION_MAJOR - major) == 3 && \ + (QEMU_VERSION_MINOR - minor) > 0)) + #define DEFINE_VIRT_MACHINE_LATEST(major, minor, latest) \ static void virt_##major##_##minor##_class_init(ObjectClass *oc, \ void *data) \ @@ -109,6 +114,9 @@ static void arm_virt_compat_set(MachineClass *mc) arm_virt_compat_set(mc); \ virt_machine_##major##_##minor##_options(mc); \ mc->desc = "QEMU " # major "." # minor " ARM Virtual Machine"; \ + if (MACHINE_IS_DEPRECATED(major, minor)) { \ + mc->deprecation_reason = "machine virt-" # major "." # minor " is not recommended for newly deployed VMs"; \ + } \ if (latest) { \ mc->alias = "virt"; \ } \ we could easily change other arches to enable the same thing. Then all we need do manually is the actual deletion. We would make it a BUILD_BUG_ON after say 20 releases to force us to remember the actual deletion at the 6 year point, without creating an immediate build fail in that exact 18th release cycle. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| _______________________________________________ Devel mailing list -- devel@xxxxxxxxxxxxxxxxx To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxx
