File feb8564a-handle-no-devmapper.patch of Package libvirt.16761

commit feb8564a3cc63bc8f68284063d53ec0d2d81a1cc
Author: Michal Prívozník <mprivozn@redhat.com>
Date:   Tue Aug 18 11:04:24 2020 +0200

    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>

Index: libvirt-5.1.0/src/util/virdevmapper.c
===================================================================
--- libvirt-5.1.0.orig/src/util/virdevmapper.c
+++ libvirt-5.1.0/src/util/virdevmapper.c
@@ -57,6 +57,9 @@ virDevMapperOnceInit(void)
     size_t i;
     int ret = -1;
 
+    if (!virFileExists(CONTROL_PATH))
+        return -2;
+
     if (virFileReadAll(PROC_DEVICES, BUF_SIZE, &buf) < 0)
         return -1;
 
@@ -139,8 +142,13 @@ 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",
@@ -340,16 +348,28 @@ virDevMapperGetTargets(const char *path,
 {
     VIR_AUTOCLOSE controlFD = -1;
     const unsigned int ttl = 32;
+    int ret;
 
     /* Arbitrary limit on recursion level. A devmapper target can
      * consist of devices or yet another targets. If that's the
      * case, we have to stop recursion somewhere. */
 
-    if (virDevMapperInitialize() < 0)
+    ret = virDevMapperInitialize();
+    if (ret == -2)
+        return 0;
+    if (ret == -1)
         return -1;
 
-    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);
 }
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