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Re: [libvirt] [PATCH] Extra filesystem options during backend filesystem mount.



Hi Daniel,

On Thu, Jul 16, 2009 at 7:46 PM, Daniel P. Berrange <berrange redhat com> wrote:
On Thu, Jul 16, 2009 at 06:06:25AM -0700, Harshavardhana wrote:
> New option index added to support -o options for various netfs.
> Currently added an option for glusterfs.

What effect does it have  ? Or why do we want/need it

Options could be required for filesystem to have few enhaced handling at the site where they will be under use. Correct approach for a configurable will be a new "XML" option in this case.

Regarding current patch:
This is required for the glusterfs to work properly with VM's.  Right now there is a
problem/difficulty in using direct-io based mechanism in the fuse kernel module
when used with "XEN" in its "tap:aio" framework, we have seen xen vms hang over glusterfs or any fuse based filesystem due to fact that fuse module doesn't yet support "aio" with O_DIRECT internally as a kernel module. To have a work around fix we have to hardcode this value due to its usage in case of VM's. 

We are currently fixing this problem by fixing directly O_DIRECT problem in fuse.
Which will be available in later releases for kernel.

So its just a glusterfs specific case.

> @@ -670,6 +692,12 @@ virStorageBackendFileSystemMount(virConnectPtr conn,
>      }
>
>      if (pool->def->type == VIR_STORAGE_POOL_NETFS) {
> +        if (pool->def->source.format = VIR_STORAGE_POOL_NETFS_GLUSTERFS) {
> +            if (virAsprintf(&options, "direct-io-mode=1") == -1) {
> +                virReportOOMError(conn);
> +                return -1;
> +            }
> +        }

Normally direct-IO mode is something you'd let apps set on a per file
basis as they desire. QEMU / Xen both know todo this, so I'm not
convinced we should force it on for the whole mount point.

Regards,
Daniel
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