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Re: [libvirt] [PATCH v3 3/4] qemu: implement on_missing



On Wed, Oct 19, 2011 at 04:42:58PM +0200, Michal Privoznik wrote:
> This patch implements on_missing feature in qemu driver.
> Upon qemu startup process an accessibility of CDROMs
> and floppy disks is checked. The source might get dropped
> if unavailable and on_missing is set accordingly.
> No event is emit thought. Look for follow up patch.
> ---
>  src/qemu/qemu_domain.c  |   66 +++++++++++++++++++++++++++++++++++++++++++++++
>  src/qemu/qemu_domain.h  |    4 +++
>  src/qemu/qemu_process.c |    4 +++
>  3 files changed, 74 insertions(+), 0 deletions(-)
> 
> diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
> index 5abc900..ffcee29 100644
> --- a/src/qemu/qemu_domain.c
> +++ b/src/qemu/qemu_domain.c
> @@ -1614,3 +1614,69 @@ qemuDomainSetFakeReboot(struct qemud_driver *driver,
>      if (virDomainSaveStatus(driver->caps, driver->stateDir, vm) < 0)
>          VIR_WARN("Failed to save status on vm %s", vm->def->name);
>  }
> +
> +int
> +qemuDomainCheckDiskPresence(struct qemud_driver *driver,
> +                            virDomainObjPtr vm,
> +                            bool being_migrated)

We do this check upon restore from save image/snapshot too,
so 'being_migrated' is a little misleading. How about
'bool start_with_state' to indicate a start attempt that
is using existing VM state.

> +{
> +    int ret = -1;
> +    int i;
> +    int accessRet;
> +    virDomainDiskDefPtr disk;
> +    char uuid[VIR_UUID_STRING_BUFLEN] ATTRIBUTE_UNUSED;
> +
> +    virUUIDFormat(vm->def->uuid, uuid);
> +
> +    for (i = 0; i < vm->def->ndisks; i++) {
> +        disk = vm->def->disks[i];
> +
> +        if (!disk->on_missing || !disk->src)
> +            continue;
> +
> +        if ((accessRet = virFileAccessibleAs(disk->src, F_OK,
> +                                             driver->user,
> +                                             driver->group)) >= 0) {
> +            /* disk accessible or virFileAccessibleAs()
> +             * terminated with signal*/
> +            continue;
> +        }

You can't assume  'disk->src' is valid. This struct field is
only valid for disks type=file|block. It will SEGV if the
type=network  (ie NBD/Ceph/Sheepdog.


> +
> +        switch (disk->on_missing) {
> +            case VIR_DOMAIN_ON_MISSING_OPTIONAL:
> +                break;
> +
> +            case VIR_DOMAIN_ON_MISSING_MANDATORY:
> +                virReportSystemError(-accessRet,
> +                                     _("cannot access file '%s'"),
> +                                     disk->src);
> +                goto cleanup;
> +                break;
> +
> +            case VIR_DOMAIN_ON_MISSING_REQUISITE:
> +                if (!being_migrated) {
> +                    virReportSystemError(-accessRet,
> +                                         _("cannot access file '%s'"),
> +                                         disk->src);
> +                    goto cleanup;
> +                }
> +                break;
> +
> +            default:
> +                qemuReportError(VIR_ERR_INTERNAL_ERROR, "%s",
> +                                _("something is tragically wrong"));
> +                goto cleanup;
> +        }
> +
> +        VIR_DEBUG("Droping disk '%s' on domain '%s' (UUID '%s') "
> +                  "due to not accessible source '%s'",
> +                  disk->dst, vm->def->name, uuid, disk->src);
> +
> +        VIR_FREE(disk->src);
> +    }
> +
> +    ret = 0;
> +
> +cleanup:
> +    return ret;
> +}


> diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
> index a7fe86c..2f1d94d 100644
> --- a/src/qemu/qemu_process.c
> +++ b/src/qemu/qemu_process.c
> @@ -2880,6 +2880,10 @@ int qemuProcessStart(virConnectPtr conn,
>                                 NULL) < 0)
>          goto cleanup;
>  
> +    VIR_DEBUG("Checking for CDROM and floppy presence");
> +    if (qemuDomainCheckDiskPresence(driver, vm, migrateFrom != NULL) < 0)
> +        goto cleanup;

This should cope with restore from save file, and incoming migration.
Does it also work with  restore from snapshot though ?

> +
>      /* If you are using a SecurityDriver with dynamic labelling,
>         then generate a security label for isolation */
>      VIR_DEBUG("Generating domain security label (if required)");


Daniel
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