[libvirt] [PATCH] lxc: Fix 'domblkstat' error with attached disk devices.

[jcfaracco at gmail.com]

From: Julio Faracco <jcfaracco at gmail.com>

LXC was not working when you attached a new disk that points to block
device. See: https://bugzilla.redhat.com/show_bug.cgi?id=1697115.
Command line from virsh was showing problems with alias first (this
feature is not supported) and after, problems to query block device. It
was happening because extra disks were not being included into
cgroup blkio.throttle properties and libvirt could not query this info.
Applying those devices into 'allowed' list is not enough, libvirt should
reset blkio.throttle as a workaround to include disks into container's
cgroup directory.

Before:

    virsh # domblkstat CentOS hda
    error: Failed to get block stats for domain 'CentOS' device 'hda'
    error: internal error: domain stats query failed

Now:

    virsh # domblkstat CentOS hda
    hda rd_req 0
    hda rd_bytes 0
    hda wr_req 0
    hda wr_bytes 0

Signed-off-by: Julio Faracco <jcfaracco at gmail.com>
---
 src/lxc/lxc_cgroup.c | 29 ++++++++++++++++++++++++++++-
 src/lxc/lxc_cgroup.h |  4 ++++
 src/lxc/lxc_driver.c |  8 ++++----
 3 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/src/lxc/lxc_cgroup.c b/src/lxc/lxc_cgroup.c
index 5efb495b56..de6d892521 100644
--- a/src/lxc/lxc_cgroup.c
+++ b/src/lxc/lxc_cgroup.c
@@ -302,6 +302,24 @@ virLXCTeardownHostUSBDeviceCgroup(virUSBDevicePtr dev G_GNUC_UNUSED,
     return 0;
 }
 
+int
+virLXCCgroupResetBlkioDeviceThrottle(virCgroupPtr cgroup,
+                                     const char *path)
+{
+    if (virCgroupSetBlkioDeviceReadBps(cgroup, path, 0) < 0)
+        return -1;
+
+    if (virCgroupSetBlkioDeviceWriteBps(cgroup, path, 0) < 0)
+        return -1;
+
+    if (virCgroupSetBlkioDeviceReadIops(cgroup, path, 0) < 0)
+        return -1;
+
+    if (virCgroupSetBlkioDeviceWriteIops(cgroup, path, 0) < 0)
+        return -1;
+
+    return 0;
+}
 
 static int virLXCCgroupSetupDeviceACL(virDomainDefPtr def,
                                       virCgroupPtr cgroup)
@@ -309,6 +327,7 @@ static int virLXCCgroupSetupDeviceACL(virDomainDefPtr def,
     int capMknod = def->caps_features[VIR_DOMAIN_CAPS_FEATURE_MKNOD];
     int ret = -1;
     size_t i;
+    const char *src_path = NULL;
     static virLXCCgroupDevicePolicy devices[] = {
         {'c', LXC_DEV_MAJ_MEMORY, LXC_DEV_MIN_NULL},
         {'c', LXC_DEV_MAJ_MEMORY, LXC_DEV_MIN_ZERO},
@@ -346,8 +365,16 @@ static int virLXCCgroupSetupDeviceACL(virDomainDefPtr def,
             !virStorageSourceIsBlockLocal(def->disks[i]->src))
             continue;
 
+        /* Workaround to include disks into blkio.throttle.
+         * To include it, we need to reset any feature of
+         * blkio.throttle.* */
+        src_path = virDomainDiskGetSource(def->disks[i]);
+        if (virLXCCgroupResetBlkioDeviceThrottle(cgroup,
+                                                 src_path) < 0)
+            goto cleanup;
+
         if (virCgroupAllowDevicePath(cgroup,
-                                     virDomainDiskGetSource(def->disks[i]),
+                                     src_path,
                                      (def->disks[i]->src->readonly ?
                                       VIR_CGROUP_DEVICE_READ :
                                       VIR_CGROUP_DEVICE_RW) |
diff --git a/src/lxc/lxc_cgroup.h b/src/lxc/lxc_cgroup.h
index 63e9e837b0..3d643a4fea 100644
--- a/src/lxc/lxc_cgroup.h
+++ b/src/lxc/lxc_cgroup.h
@@ -46,3 +46,7 @@ int
 virLXCTeardownHostUSBDeviceCgroup(virUSBDevicePtr dev,
                                   const char *path,
                                   void *opaque);
+
+int
+virLXCCgroupResetBlkioDeviceThrottle(virCgroupPtr cgroup,
+                                     const char *path);
diff --git a/src/lxc/lxc_driver.c b/src/lxc/lxc_driver.c
index 204a3ed522..87da55f308 100644
--- a/src/lxc/lxc_driver.c
+++ b/src/lxc/lxc_driver.c
@@ -2339,14 +2339,14 @@ lxcDomainBlockStats(virDomainPtr dom,
         goto endjob;
     }
 
-    if (!disk->info.alias) {
+    if (!disk->src->path) {
         virReportError(VIR_ERR_INTERNAL_ERROR,
                        _("missing disk device alias name for %s"), disk->dst);
         goto endjob;
     }
 
     ret = virCgroupGetBlkioIoDeviceServiced(priv->cgroup,
-                                            disk->info.alias,
+                                            disk->src->path,
                                             &stats->rd_bytes,
                                             &stats->wr_bytes,
                                             &stats->rd_req,
@@ -2424,14 +2424,14 @@ lxcDomainBlockStatsFlags(virDomainPtr dom,
             goto endjob;
         }
 
-        if (!disk->info.alias) {
+        if (!disk->src->path) {
             virReportError(VIR_ERR_INTERNAL_ERROR,
                            _("missing disk device alias name for %s"), disk->dst);
             goto endjob;
         }
 
         if (virCgroupGetBlkioIoDeviceServiced(priv->cgroup,
-                                              disk->info.alias,
+                                              disk->src->path,
                                               &rd_bytes,
                                               &wr_bytes,
                                               &rd_req,
-- 
2.20.1