On Wed, Nov 25, 2009 at 10:31:03AM +0100, Daniel Veillard wrote:
On Wed, Nov 25, 2009 at 09:27:13AM +0200, Dan Kenigsberg wrote:
this is particularily important if said device is a file sitting on a root_squashing nfs export.
my previous attempt for a patch missed 3 chowns that should be avoided. --- src/qemu/qemu.conf | 4 ++++ src/qemu/qemu_conf.c | 3 +++ src/qemu/qemu_conf.h | 1 + src/qemu/qemu_driver.c | 8 ++++---- 4 files changed, 12 insertions(+), 4 deletions(-)
diff --git a/src/qemu/qemu.conf b/src/qemu/qemu.conf index bca858a..892a50b 100644 --- a/src/qemu/qemu.conf +++ b/src/qemu/qemu.conf @@ -96,6 +96,10 @@ # The group ID for QEMU processes run by the system instance #group = "root"
+# should libvirt assume that devices are accessible to the above user:group. +# by default, libvirt tries to chown devices before starting up a domain and +# restore ownership to root when domain comes down. +#assume_devices_accessible = 0
# What cgroup controllers to make use of with QEMU guests # diff --git a/src/qemu/qemu_conf.c b/src/qemu/qemu_conf.c index b1b9e5f..520a395 100644 --- a/src/qemu/qemu_conf.c +++ b/src/qemu/qemu_conf.c @@ -232,6 +232,9 @@ int qemudLoadDriverConfig(struct qemud_driver *driver, return -1; }
+ p = virConfGetValue (conf, "assume_devices_accessible"); + CHECK_TYPE ("assume_devices_accessible", VIR_CONF_LONG); + if (p) driver->avoid_dev_chown = p->l;
an explicit initialization of the field would be better if p is NULL.
if (virGetGroupID(NULL, group, &driver->group) < 0) { VIR_FREE(group); diff --git a/src/qemu/qemu_conf.h b/src/qemu/qemu_conf.h index 675c636..3a9da73 100644 --- a/src/qemu/qemu_conf.h +++ b/src/qemu/qemu_conf.h @@ -87,6 +87,7 @@ struct qemud_driver {
uid_t user; gid_t group; + int avoid_dev_chown;
unsigned int qemuVersion; int nextvmid; diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c index 2f273eb..5f02aa2 100644 --- a/src/qemu/qemu_driver.c +++ b/src/qemu/qemu_driver.c @@ -1968,7 +1968,7 @@ static int qemuDomainSetDeviceOwnership(virConnectPtr conn, uid_t uid; gid_t gid;
- if (!driver->privileged) + if (!driver->privileged || driver->avoid_dev_chown) return 0;
/* short circuit case of root:root */ @@ -2002,7 +2002,7 @@ static int qemuDomainSetAllDeviceOwnership(virConnectPtr conn, uid_t uid; gid_t gid;
- if (!driver->privileged) + if (!driver->privileged || driver->avoid_dev_chown) return 0;
/* short circuit case of root:root */ @@ -3438,7 +3438,7 @@ static int qemudDomainSave(virDomainPtr dom, } fd = -1;
- if (driver->privileged && + if (driver->privileged && !driver->avoid_dev_chown && chown(path, driver->user, driver->group) < 0) { virReportSystemError(NULL, errno, _("unable to set ownership of '%s' to user %d:%d"), @@ -3473,7 +3473,7 @@ static int qemudDomainSave(virDomainPtr dom, if (rc < 0) goto endjob;
- if (driver->privileged && + if (driver->privileged && !driver->avoid_dev_chown && chown(path, 0, 0) < 0) { virReportSystemError(NULL, errno, _("unable to set ownership of '%s' to user %d:%d"),
The core question is having this as another manual user tweak, it always makes me a bit uncomfortable if proper working of software requires manually editing a config file. If we really need this kind of options for proper operations in specific conditions can we make sure it can be set via APIs too ? I don't think we should expose something as generic as the internal Conf APIs, but these runtime option in src/qemu/qemu.conf start to accumulate and I start to wonder how to properly manage all this.
Aren't we here to babysit software? :-) For this particular behavior, I personally feel that the default is wrong. I don't like it that libvirt takes the liberty to (try to) change ownership, I like it less when it does not truely restore ownership, and even less, that it fails to use files over nfs. I understand that this behavior was meant to assist admins who upgrade from running qemu as root to running it as a meager user. But personally I believe that we could have politely asked them: if you use this new feature, please make sure this new qemu user has access to your files/devices. Now that there are people expecting current behavior, I don't really see a nice way out. Dan