From b38ab86a0a2cf3453d37a5fe96b2e022d8a1d48a Mon Sep 17 00:00:00 2001
Message-Id: <b38ab86a0a2cf3453d37a5fe96b2e022d8a1d48a@dist-git>
From: Michal Privoznik <mprivozn@redhat.com>
Date: Tue, 25 Aug 2020 17:16:07 +0200
Subject: [PATCH] virdevmapper: Ignore all errors when opening
 /dev/mapper/control

So far, only ENOENT is ignored (to deal with kernels without
devmapper). However, as reported on the list, under certain
scenarios a different error can occur. For instance, when libvirt
is running inside a container which doesn't have permissions to
talk to the devmapper. If this is the case, then open() returns
-1 and sets errno=EPERM.

Assuming that multipath devices are fairly narrow use case and
using them in a restricted container is even more narrow the best
fix seems to be to ignore all open errors BUT produce a warning
on failure. To avoid flooding logs with warnings on kernels
without devmapper the level is reduced to a plain debug message.

Reported-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
Reviewed-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
(cherry picked from commit 53d9af1e7924757e3b5f661131dd707d7110d094)

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1860421

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Message-Id: <e1b69d69e7d242829995208c6d59ed0477208920.1598364552.git.mprivozn@redhat.com>
Reviewed-by: Jiri Denemark <jdenemar@redhat.com>
---
 src/util/virdevmapper.c | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/src/util/virdevmapper.c b/src/util/virdevmapper.c
index a81e2edee4..ee2fab5ae3 100644
--- a/src/util/virdevmapper.c
+++ b/src/util/virdevmapper.c
@@ -35,9 +35,12 @@
 # include "viralloc.h"
 # include "virstring.h"
 # include "virfile.h"
+# include "virlog.h"
 
 # define VIR_FROM_THIS VIR_FROM_STORAGE
 
+VIR_LOG_INIT("util.virdevmapper");
+
 # define PROC_DEVICES "/proc/devices"
 # define DM_NAME "device-mapper"
 # define DEV_DM_DIR "/dev/" DM_DIR
@@ -130,11 +133,15 @@ virDMOpen(void)
     memset(&dm, 0, sizeof(dm));
 
     if ((controlFD = open(CONTROL_PATH, O_RDWR)) < 0) {
-        if (errno == ENOENT)
-            return -2;
-
-        virReportSystemError(errno, _("Unable to open %s"), CONTROL_PATH);
-        return -1;
+        /* We can't talk to devmapper. Produce a warning and let
+         * the caller decide what to do next. */
+        if (errno == ENOENT) {
+            VIR_DEBUG("device mapper not available");
+        } else {
+            VIR_WARN("unable to open %s: %s",
+                     CONTROL_PATH, g_strerror(errno));
+        }
+        return -2;
     }
 
     if (!virDMIoctl(controlFD, DM_VERSION, &dm, &tmp)) {
@@ -310,9 +317,9 @@ virDevMapperGetTargets(const char *path,
 
     if ((controlFD = virDMOpen()) < 0) {
         if (controlFD == -2) {
-            /* The CONTROL_PATH doesn't exist. Probably the
-             * module isn't loaded, yet. Don't error out, just
-             * exit. */
+            /* The CONTROL_PATH doesn't exist or is unusable.
+             * Probably the module isn't loaded, yet. Don't error
+             * out, just exit. */
             return 0;
         }
 
-- 
2.28.0