From 8474f0f611f4372bd4f98c6df92f50566f631db0 Mon Sep 17 00:00:00 2001
Message-Id: <8474f0f611f4372bd4f98c6df92f50566f631db0@dist-git>
From: Michal Privoznik <mprivozn@redhat.com>
Date: Mon, 8 Mar 2021 12:57:33 +0100
Subject: [PATCH] virdevmapper: Handle kernel without device-mapper support
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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=1933557
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Message-Id: <11f41c0fd7b7c8365e24398173cb0bb2f8e785de.1615203117.git.mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@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 725de736c1..a76fe95922 100644
--- a/src/util/virdevmapper.c
+++ b/src/util/virdevmapper.c
@@ -57,6 +57,9 @@ 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;
 
@@ -130,8 +133,13 @@ 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",
@@ -313,8 +321,16 @@ 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);
 }
-- 
2.31.0