Hi,

if you run any domain specific xl command with an invalid (aka 
non-existing) numeric domain ID, the command does not abort, but 
proceeds with some bogus number:
# xl destroy 42
libxl: error: libxl.c:692:libxl_domain_destroy xc_domain_pause failed for 42
libxl: error: libxl_dm.c:705:libxl__destroy_device_model Couldn't find 
device model's pid: No such file or directory
libxl: error: libxl.c:696:libxl_domain_destroy 
libxl__destroy_device_model failed for 42
libxl: error: libxl_device.c:325:libxl__devices_destroy 
/local/domain/42/device is empty
libxl: error: libxl_dom.c:536:userdata_path unable to find domain info 
for domain 42: Success
libxl: error: libxl.c:713:libxl_domain_destroy xc_domain_destroy failed 
for 42

The attached patch catches a non-existing domain and returns early (as 
an invalid domain _name_ would do).
Please apply to Xen 4.1.0-rc.

Signed-off-by: Andre Przywara <andre.przywara@amd.com>

-- 
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany