Starting from commit 2e82c18c in Xen (will be included in Xen 4.4) libxl_get_max_cpus() start returning a proper libxl error code, in case of failure. It returning 0 is now basically impossible but, theoretically, still wrong, not to mention that using '<= 0' makes this correct for both Xen 4.4 and Xen 4.3 (and 4.2). That's why we go for it (rather than just '< 0'). Signed-off-by: Dario Faggioli <dario.faggioli(a)citrix.com&gt; Cc: Jim Fehlig <jfehlig(a)suse.com&gt; Cc: Ian Jackson <Ian.Jackson(a)eu.citrix.com&gt; --- src/libxl/libxl_driver.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/src/libxl/libxl_driver.c b/src/libxl/libxl_driver.c index 692c3b7..a31b094 100644 --- a/src/libxl/libxl_driver.c +++ b/src/libxl/libxl_driver.c @@ -1101,9 +1101,11 @@ libxlConnectGetMaxVcpus(virConnectPtr conn, const char *type ATTRIBUTE_UNUSED) cfg = libxlDriverConfigGet(driver); ret = libxl_get_max_cpus(cfg->ctx); - /* libxl_get_max_cpus() will return 0 if there were any failures, - e.g. xc_physinfo() failing */ - if (ret == 0) + /* On failure, libxl_get_max_cpus() will return ERROR_FAIL from Xen 4.4 + * onward, but it ever returning 0 is obviously wrong too (and it is + * what happens, on failure, on Xen 4.3 and earlier). Therefore, a 'less + * or equal' is the catchall we want. */ + if (ret <= 0) ret = -1; virObjectUnref(cfg);