[libvirt] [PATCH] qemuDomainRemoveMemoryDevice: unlink() memory backing file

[Daniel P. Berrange]

On Thu, Jan 11, 2018 at 01:24:57PM +0100, Michal Privoznik wrote:
> https://bugzilla.redhat.com/show_bug.cgi?id=1461214
> 
> Since fec8f9c49af we try to use predictable file names for
> 'memory-backend-file' objects. But that made us provide full path
> to qemu when hot plugging the object while previously we provided
> merely a directory. But this makes qemu behave differently. If
> qemu sees a path terminated with a directory it calls mkstemp()
> and unlinks the file immediately. But if it sees full path it
> just calls open(path, O_CREAT ..); and never unlinks the file.
> Therefore it's up to libvirt to unlink the file and not leave it
> behind.

IIUC, this unlinks the file when QEMU shuts down (or the mem device is
unplugged).

Is there any benefit and/or downside to doing the same as QEMU and
unlinking it immediately after QEMU has opened it ? I guess figuring
out the right time might be hard todo race-free.

> 
> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> ---
> 
> Zack, can you please check if this patch is suitable for your use cases?
> 
>  src/qemu/qemu_hotplug.c |  3 +++
>  src/qemu/qemu_process.c | 26 ++++++++++++++++++++++++++
>  src/qemu/qemu_process.h |  4 ++++
>  3 files changed, 33 insertions(+)
> 
> diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c
> index 6dc16a105..f26e2ca60 100644
> --- a/src/qemu/qemu_hotplug.c
> +++ b/src/qemu/qemu_hotplug.c
> @@ -3894,6 +3894,9 @@ qemuDomainRemoveMemoryDevice(virQEMUDriverPtr driver,
>      if (qemuDomainNamespaceTeardownMemory(vm, mem) <  0)
>          VIR_WARN("Unable to remove memory device from /dev");
>  
> +    if (qemuProcessDestroyMemoryBackingPath(driver, vm, mem) < 0)
> +        VIR_WARN("Unable to destroy memory backing path");
> +
>      virDomainMemoryDefFree(mem);
>  
>      /* fix the balloon size */
> diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
> index 1a0923af3..73624eefe 100644
> --- a/src/qemu/qemu_process.c
> +++ b/src/qemu/qemu_process.c
> @@ -3467,6 +3467,32 @@ qemuProcessBuildDestroyMemoryPaths(virQEMUDriverPtr driver,
>  }
>  
>  
> +int
> +qemuProcessDestroyMemoryBackingPath(virQEMUDriverPtr driver,
> +                                    virDomainObjPtr vm,
> +                                    virDomainMemoryDefPtr mem)
> +{
> +    virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
> +    char *path = NULL;
> +    int ret = -1;
> +
> +    if (qemuGetMemoryBackingPath(vm->def, cfg, mem->info.alias, &path) < 0)
> +        goto cleanup;
> +
> +    if (unlink(path) < 0 &&
> +        errno != ENOENT) {
> +        virReportSystemError(errno, _("Unable to remove %s"), path);
> +        goto cleanup;
> +    }
> +
> +    ret = 0;
> + cleanup:
> +    VIR_FREE(path);
> +    virObjectUnref(cfg);
> +    return ret;
> +}
> +
> +
>  static int
>  qemuProcessVNCAllocatePorts(virQEMUDriverPtr driver,
>                              virDomainGraphicsDefPtr graphics,
> diff --git a/src/qemu/qemu_process.h b/src/qemu/qemu_process.h
> index cd9a72031..3fc7d6c85 100644
> --- a/src/qemu/qemu_process.h
> +++ b/src/qemu/qemu_process.h
> @@ -43,6 +43,10 @@ int qemuProcessBuildDestroyMemoryPaths(virQEMUDriverPtr driver,
>                                         virDomainMemoryDefPtr mem,
>                                         bool build);
>  
> +int qemuProcessDestroyMemoryBackingPath(virQEMUDriverPtr driver,
> +                                        virDomainObjPtr vm,
> +                                        virDomainMemoryDefPtr mem);
> +
>  void qemuProcessAutostartAll(virQEMUDriverPtr driver);
>  void qemuProcessReconnectAll(virConnectPtr conn, virQEMUDriverPtr driver);
>  
> -- 
> 2.13.6
> 
> --
> libvir-list mailing list
> libvir-list at redhat.com
> https://www.redhat.com/mailman/listinfo/libvir-list

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 :|