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>

diff --git a/src/util/virdevmapper.c b/src/util/virdevmapper.c
index b24d9377f82085e25458e0b8e90212de45f5b62c..3cc399f38202025918a8a113fdb27556029fbd4c 100644 (file)
--- 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",
@@ -299,8 +307,16 @@ 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);
 }