From a9c950dcbac1f708bcd01111d4ec9b550db37fe3 Mon Sep 17 00:00:00 2001
Message-Id: <a9c950dcbac1f708bcd01111d4ec9b550db37fe3@dist-git>
From: Michal Privoznik <mprivozn@redhat.com>
Date: Tue, 25 Aug 2020 17:16:06 +0200
Subject: [PATCH] virdevmapper: Handle kernel without device-mapper support

In one of my latest patch (v6.6.0~30) I was trying to remove
libdevmapper use in favor of our own implementation. However, the
code did not take into account that device mapper can be not
compiled into the kernel (e.g. be a separate module that's not
loaded) in which case /proc/devices won't have the device-mapper
major number and thus virDevMapperGetTargets() and/or
virIsDevMapperDevice() fails.

However, such failure is safe to ignore, because if device mapper
is missing then there can't be any multipath devices and thus we
don't need to allow the deps in CGroups, nor create them in the
domain private namespace, etc.

Fixes: 22494556542c676d1b9e7f1c1f2ea13ac17e1e3e
Reported-by: Andrea Bolognani <abologna@redhat.com>
Reported-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
Tested-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
(cherry picked from commit feb8564a3cc63bc8f68284063d53ec0d2d81a1cc)

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

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Message-Id: <71fcd93071dffdf4942ccce8671af7fcbcec397f.1598364552.git.mprivozn@redhat.com>
Reviewed-by: Jiri Denemark <jdenemar@redhat.com>
---
 src/util/virdevmapper.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/src/util/virdevmapper.c b/src/util/virdevmapper.c
index b43dbefa9a..a81e2edee4 100644
--- a/src/util/virdevmapper.c
+++ b/src/util/virdevmapper.c
@@ -54,6 +54,9 @@ virDevMapperGetMajor(unsigned int *major)
     VIR_AUTOSTRINGLIST lines = NULL;
     size_t i;
 
+    if (!virFileExists(CONTROL_PATH))
+        return -2;
+
     if (virFileReadAll(PROC_DEVICES, BUF_SIZE, &buf) < 0)
         return -1;
 
@@ -126,8 +129,13 @@ virDMOpen(void)
 
     memset(&dm, 0, sizeof(dm));
 
-    if ((controlFD = open(CONTROL_PATH, O_RDWR)) < 0)
+    if ((controlFD = open(CONTROL_PATH, O_RDWR)) < 0) {
+        if (errno == ENOENT)
+            return -2;
+
+        virReportSystemError(errno, _("Unable to open %s"), CONTROL_PATH);
         return -1;
+    }
 
     if (!virDMIoctl(controlFD, DM_VERSION, &dm, &tmp)) {
         virReportSystemError(errno, "%s",
@@ -300,8 +308,16 @@ virDevMapperGetTargets(const char *path,
      * consist of devices or yet another targets. If that's the
      * case, we have to stop recursion somewhere. */
 
-    if ((controlFD = virDMOpen()) < 0)
+    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. */
+            return 0;
+        }
+
         return -1;
+    }
 
     return virDevMapperGetTargetsImpl(controlFD, path, devPaths, ttl);
 }
-- 
2.28.0