virtio-9p: Introduces an option to specify the security model.

The new option is:

-fsdev fstype,id=myid,path=/share_path/,security_model=[mapped|passthrough]
-virtfs fstype,path=/share_path/,security_model=[mapped|passthrough],mnt_tag=tag

In the case of mapped security model, files are created with QEMU user
credentials and the client-user's credentials are saved in extended attributes.
Whereas in the case of passthrough security model, files on the
filesystem are directly created with client-user's credentials.

Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

fsdev/qemu-fsdev.h

@@ -40,6 +40,7 @@ typedef struct FsTypeTable {
 typedef struct FsTypeEntry {
     char *fsdev_id;
     char *path;
+    char *security_model;
     FileOperations *ops;
 } FsTypeEntry;