[RFC] qemu: Check for changes in qemu modules directory

[Jim Fehlig]

Hi All,

Any comments on this RFC patch? Is this something we would like to see in the 
6.7.0 release?

On 8/20/20 5:03 PM, Jim Fehlig wrote:
> Add a configuration option for specifying location of the qemu modules
> directory, defaulting to /usr/lib64/qemu. Then use this location to
> check for changes in the directory, indicating that a qemu module has
> changed and capabilities need to be reprobed.
> 
> Signed-off-by: Jim Fehlig <jfehlig at suse.com>
> ---
> 
> This is a mildly tested impl of the idea discussed here (and elsewhere
> in the thread)
> 
> https://www.redhat.com/archives/libvir-list/2020-August/msg00684.html
> 
> I've checked that both system and session caches are updated when a
> qemu modules package is updated. I'll do some more testing but wanted
> to send the patch for early comments. Testing in other environments
> would be much appreciated. Thanks!

I've tried some more configurations and haven't noticed any problems with the 
patch thus far. The request for additional eyeballs and testing still valid 
though :-).

Regards,
Jim

> 
>   meson.build                  |  6 ++++++
>   meson_options.txt            |  1 +
>   src/qemu/qemu_capabilities.c | 35 +++++++++++++++++++++++++++++++++++
>   3 files changed, 42 insertions(+)
> 
> diff --git a/meson.build b/meson.build
> index a72d0c0e85..16928482aa 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -1745,6 +1745,12 @@ if not get_option('driver_qemu').disabled()
>     if use_qemu
>       conf.set('WITH_QEMU', 1)
>   
> +    qemu_moddir = get_option('qemu_moddir')
> +    if qemu_moddir == ''
> +      qemu_moddir = '/usr/lib64/qemu'
> +    endif
> +    conf.set_quoted('QEMU_MODDIR', qemu_moddir)
> +
>       if host_machine.system() in ['freebsd', 'darwin']
>         default_qemu_user = 'root'
>         default_qemu_group = 'wheel'
> diff --git a/meson_options.txt b/meson_options.txt
> index c538d323c1..cedbd79491 100644
> --- a/meson_options.txt
> +++ b/meson_options.txt
> @@ -59,6 +59,7 @@ option('driver_openvz', type: 'feature', value: 'auto', description: 'OpenVZ dri
>   option('driver_qemu', type: 'feature', value: 'auto', description: 'QEMU/KVM driver')
>   option('qemu_user', type: 'string', value: '', description: 'username to run QEMU system instance as')
>   option('qemu_group', type: 'string', value: '', description: 'groupname to run QEMU system instance as')
> +option('qemu_moddir', type: 'string', value: '', description: 'set the directory where QEMU modules are located')
>   option('driver_remote', type: 'feature', value: 'enabled', description: 'remote driver')
>   option('remote_default_mode', type: 'combo', choices: ['legacy', 'direct'], value: 'legacy', description: 'remote driver default mode')
>   option('driver_secrets', type: 'feature', value: 'auto', description: 'local secrets management driver')
> diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
> index ff6ba8c9e9..a00853c753 100644
> --- a/src/qemu/qemu_capabilities.c
> +++ b/src/qemu/qemu_capabilities.c
> @@ -677,6 +677,7 @@ struct _virQEMUCaps {
>       char *binary;
>       time_t ctime;
>       time_t libvirtCtime;
> +    time_t modDirMtime;
>       bool invalidation;
>   
>       virBitmapPtr flags;
> @@ -4194,6 +4195,7 @@ virQEMUCapsParseSEVInfo(virQEMUCapsPtr qemuCaps, xmlXPathContextPtr ctxt)
>    * <qemuCaps>
>    *   <emulator>/some/path</emulator>
>    *   <qemuctime>234235253</qemuctime>
> + *   <qemumoddirmtime>234235253</qemumoddirmtime>
>    *   <selfctime>234235253</selfctime>
>    *   <selfvers>1002016</selfvers>
>    *   <flag name='foo'/>
> @@ -4283,6 +4285,9 @@ virQEMUCapsLoadCache(virArch hostArch,
>       }
>       qemuCaps->ctime = (time_t)l;
>   
> +    if (virXPathLongLong("string(./qemumoddirmtime)", ctxt, &l) == 0)
> +        qemuCaps->modDirMtime = (time_t)l;
> +
>       if ((n = virXPathNodeSet("./flag", ctxt, &nodes)) < 0) {
>           virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
>                          _("failed to parse qemu capabilities flags"));
> @@ -4615,6 +4620,10 @@ virQEMUCapsFormatCache(virQEMUCapsPtr qemuCaps)
>                             qemuCaps->binary);
>       virBufferAsprintf(&buf, "<qemuctime>%llu</qemuctime>\n",
>                         (long long)qemuCaps->ctime);
> +    if (qemuCaps->modDirMtime > 0) {
> +        virBufferAsprintf(&buf, "<qemumoddirmtime>%llu</qemumoddirmtime>\n",
> +                          (long long)qemuCaps->modDirMtime);
> +    }
>       virBufferAsprintf(&buf, "<selfctime>%llu</selfctime>\n",
>                         (long long)qemuCaps->libvirtCtime);
>       virBufferAsprintf(&buf, "<selfvers>%lu</selfvers>\n",
> @@ -4881,6 +4890,23 @@ virQEMUCapsIsValid(void *data,
>       if (!qemuCaps->binary)
>           return true;
>   
> +    if (virFileExists(QEMU_MODDIR)) {
> +        if (stat(QEMU_MODDIR, &sb) < 0) {
> +            VIR_DEBUG("Failed to stat QEMU module directory '%s': %s",
> +                      QEMU_MODDIR,
> +                      g_strerror(errno));
> +            return false;
> +        }
> +
> +        if (sb.st_mtime != qemuCaps->modDirMtime) {
> +            VIR_DEBUG("Outdated capabilities for '%s': QEMU modules "
> +                      "directory '%s' changed (%lld vs %lld)",
> +                      qemuCaps->binary, QEMU_MODDIR,
> +                      (long long)sb.st_mtime, (long long)qemuCaps->modDirMtime);
> +            return false;
> +        }
> +    }
> +
>       if (qemuCaps->libvirtCtime != virGetSelfLastChanged() ||
>           qemuCaps->libvirtVersion != LIBVIR_VERSION_NUMBER) {
>           VIR_DEBUG("Outdated capabilities for '%s': libvirt changed "
> @@ -5463,6 +5489,15 @@ virQEMUCapsNewForBinaryInternal(virArch hostArch,
>           goto error;
>       }
>   
> +    if (virFileExists(QEMU_MODDIR)) {
> +        if (stat(QEMU_MODDIR, &sb) < 0) {
> +            virReportSystemError(errno, _("Cannot check QEMU module directory %s"),
> +                                 QEMU_MODDIR);
> +            goto error;
> +        }
> +        qemuCaps->modDirMtime = sb.st_mtime;
> +    }
> +
>       if (virQEMUCapsInitQMP(qemuCaps, libDir, runUid, runGid) < 0)
>           goto error;
>   
>