Re: [libvirt] [Xen-devel] libvirt: [PATCH] libxl: Check for control_d string to decide about dom0

On 12.03.2014 13:08, Ian Campbell wrote: > On Wed, 2014-03-12 at 13:03 +0100, Stefan Bader wrote: > >> I have been looking into a bug report (see BugLink) which reported >> libvirt to fail starting inside a Xen guest. Upon further investigation >> I found that some tools that help monitoring Xen guests will mount >> xenfs to /proc/xen. This will create a capabilities files there even >> if the guest is not dom0. However it will return nothing when reading >> from it. >> > This seems consistent with the xencommons initscript which does: > # run this script only in dom0: > # no capabilities file in xenlinux domU kernel > # empty capabilities file in pv_ops domU kernel > if test -f /proc/xen/capabilities && \ > ! grep -q "control_d" /proc/xen/capabilities ; then > exit 0 > fi > > >> Ian, just to sanity check myself. I looked at the xenfs code and to >> me there only seem to be those two outcomes (either "control_d" for >> running in dom0 or notrhing if not). >> >> With the following patch applied, libvirt starts up correctly in >> the normal guests (with xenfs mounted) without initializing libxl. >> And also in dom0 where it still enables the libxl driver (if the >> xl toolstack is selected). >> >> -Stefan >> >> From f11949caca6dfe1a802472a2a6d4fe760115ccc6 Mon Sep 17 00:00:00 2001 >> From: Stefan Bader <stefan.bader(a)canonical.com&gt; >> Date: Wed, 12 Mar 2014 11:37:16 +0100 >> Subject: [PATCH] libxl: Check for control_d string to decide about dom0 >> >> As soon as any guest mounts xenfs to /proc/xen, there is a capabilities >> file in that directory. However it returns nothing when reading from it. >> Change the test to actually check the contents of the file. >> >> BugLink: http://bugs.launchpad.net/bugs/1248025 >> >> Signed-off-by: Stefan Bader <stefan.bader(a)canonical.com&gt; >> --- >> src/libxl/libxl_driver.c | 14 ++++++++++++-- >> 1 file changed, 12 insertions(+), 2 deletions(-) >> >> diff --git a/src/libxl/libxl_driver.c b/src/libxl/libxl_driver.c >> index 65d80a2..844e828 100644 >> --- a/src/libxl/libxl_driver.c >> +++ b/src/libxl/libxl_driver.c >> @@ -944,6 +944,7 @@ libxlDriverShouldLoad(bool privileged) >> bool ret = false; >> virCommandPtr cmd; >> int status; >> + char *output = NULL; >> >> /* Don't load if non-root */ >> if (!privileged) { >> @@ -951,8 +952,17 @@ libxlDriverShouldLoad(bool privileged) >> return ret; >> } >> >> - /* Don't load if not running on a Xen control domain (dom0) */ >> - if (!virFileExists("/proc/xen/capabilities")) { >> + /* >> + * Don't load if not running on a Xen control domain (dom0). It is not >> + * sufficient to check for the file to exist as any guest can mount >> + * xenfs to /proc/xen. >> + */ >> + status = virFileReadAll("/proc/xen/capabilities", 10. &output); >> > Is this "." supposed to be a ","? > Darn, I thought I had fixed that. Unfortunately in the wrong place. Yes, that should be a ",". Sorry