util: Introduce virDevMapperGetTargets

This helper fetches dependencies for given device mapper target.

At the same time, we need to provide a dummy log function because
by default libdevmapper prints out error messages to stderr which
we need to suppress.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

src/libvirt_private.syms

@@ -1670,6 +1670,10 @@ virDBusMessageUnref;
 virDBusSetSharedBus;
 
 
+# util/virdevmapper.h
+virDevMapperGetTargets;
+
+
 # util/virdnsmasq.h
 dnsmasqAddDhcpHost;
 dnsmasqAddHost;

src/util/Makefile.inc.am

@@ -35,6 +35,8 @@ UTIL_SOURCES = \
 	util/virdbus.c \
 	util/virdbus.h \
 	util/virdbuspriv.h \
+	util/virdevmapper.c \
+	util/virdevmapper.h \
 	util/virdnsmasq.c \
 	util/virdnsmasq.h \
 	util/virebtables.c \

src/util/virdevmapper.c

@@ -0,0 +1,199 @@
+/*
+ * virdevmapper.c: Functions for handling device mapper
+ *
+ * Copyright (C) 2018 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library.  If not, see
+ * <http://www.gnu.org/licenses/>.
+ *
+ * Authors:
+ *     Michal Privoznik <mprivozn@redhat.com>
+ */
+
+#include <config.h>
+
+#ifdef MAJOR_IN_MKDEV
+# include <sys/mkdev.h>
+#elif MAJOR_IN_SYSMACROS
+# include <sys/sysmacros.h>
+#endif
+
+#ifdef WITH_DEVMAPPER
+# include <libdevmapper.h>
+#endif
+
+#include "virdevmapper.h"
+#include "internal.h"
+#include "virthread.h"
+#include "viralloc.h"
+#include "virstring.h"
+
+#ifdef WITH_DEVMAPPER
+static void
+virDevMapperDummyLogger(int level ATTRIBUTE_UNUSED,
+                        const char *file ATTRIBUTE_UNUSED,
+                        int line ATTRIBUTE_UNUSED,
+                        int dm_errno ATTRIBUTE_UNUSED,
+                        const char *fmt ATTRIBUTE_UNUSED,
+                        ...)
+{
+    return;
+}
+
+static int
+virDevMapperOnceInit(void)
+{
+    /* Ideally, we would not need this. But libdevmapper prints
+     * error messages to stderr by default. Sad but true. */
+    dm_log_with_errno_init(virDevMapperDummyLogger);
+    return 0;
+}
+
+
+VIR_ONCE_GLOBAL_INIT(virDevMapper)
+
+
+static int
+virDevMapperGetTargetsImpl(const char *path,
+                           char ***devPaths_ret,
+                           unsigned int ttl)
+{
+    struct dm_task *dmt = NULL;
+    struct dm_deps *deps;
+    struct dm_info info;
+    char **devPaths = NULL;
+    char **recursiveDevPaths = NULL;
+    size_t i;
+    int ret = -1;
+
+    *devPaths_ret = NULL;
+
+    if (virDevMapperInitialize() < 0)
+        return ret;
+
+    if (ttl == 0) {
+        errno = ELOOP;
+        return ret;
+    }
+
+    if (!(dmt = dm_task_create(DM_DEVICE_DEPS)))
+        return ret;
+
+    if (!dm_task_set_name(dmt, path)) {
+        if (errno == ENOENT) {
+            /* It's okay, @path is not managed by devmapper =>
+             * not a devmapper device. */
+            ret = 0;
+        }
+        goto cleanup;
+    }
+
+    dm_task_no_open_count(dmt);
+
+    if (!dm_task_run(dmt))
+        goto cleanup;
+
+    if (!dm_task_get_info(dmt, &info))
+        goto cleanup;
+
+    if (!info.exists) {
+        ret = 0;
+        goto cleanup;
+    }
+
+    if (!(deps = dm_task_get_deps(dmt)))
+        goto cleanup;
+
+    if (VIR_ALLOC_N_QUIET(devPaths, deps->count + 1) < 0)
+        goto cleanup;
+
+    for (i = 0; i < deps->count; i++) {
+        if (virAsprintfQuiet(&devPaths[i], "/dev/block/%u:%u",
+                             major(deps->device[i]),
+                             minor(deps->device[i])) < 0)
+            goto cleanup;
+    }
+
+    recursiveDevPaths = NULL;
+    for (i = 0; i < deps->count; i++) {
+        char **tmpPaths;
+
+        if (virDevMapperGetTargetsImpl(devPaths[i], &tmpPaths, ttl - 1) < 0)
+            goto cleanup;
+
+        if (tmpPaths &&
+            virStringListMerge(&recursiveDevPaths, &tmpPaths) < 0) {
+            virStringListFree(tmpPaths);
+            goto cleanup;
+        }
+    }
+
+    if (virStringListMerge(&devPaths, &recursiveDevPaths) < 0)
+        goto cleanup;
+
+    VIR_STEAL_PTR(*devPaths_ret, devPaths);
+    ret = 0;
+ cleanup:
+    virStringListFree(recursiveDevPaths);
+    virStringListFree(devPaths);
+    dm_task_destroy(dmt);
+    return ret;
+}
+
+
+/**
+ * virDevMapperGetTargets:
+ * @path: devmapper target
+ * @devPaths: returned string list of devices
+ *
+ * For given @path figure out its targets, and store them in
+ * @devPaths array. Note, @devPaths is a string list so it's NULL
+ * terminated.
+ *
+ * If @path is not a devmapper device, @devPaths is set to NULL and
+ * success is returned.
+ *
+ * If @path consists of yet another devmapper targets these are
+ * consulted recursively.
+ *
+ * If we don't have permissions to talk to kernel, -1 is returned
+ * and errno is set to EBADF.
+ *
+ * Returns 0 on success,
+ *        -1 otherwise (with errno set, no libvirt error is
+ *        reported)
+ */
+int
+virDevMapperGetTargets(const char *path,
+                       char ***devPaths)
+{
+    const unsigned int ttl = 32;
+
+    /* 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. */
+
+    return virDevMapperGetTargetsImpl(path, devPaths, ttl);
+}
+
+#else /* ! WITH_DEVMAPPER */
+
+int
+virDevMapperGetTargets(const char *path ATTRIBUTE_UNUSED,
+                       char ***devPaths ATTRIBUTE_UNUSED)
+{
+    errno = ENOSYS;
+    return -1;
+}
+#endif /* ! WITH_DEVMAPPER */

src/util/virdevmapper.h

@@ -0,0 +1,31 @@
+/*
+ * virdevmapper.h: Functions for handling device mapper
+ *
+ * Copyright (C) 2018 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library.  If not, see
+ * <http://www.gnu.org/licenses/>.
+ *
+ * Authors:
+ *     Michal Privoznik <mprivozn@redhat.com>
+ */
+
+#ifndef __VIR_DEVMAPPER_H__
+# define __VIR_DEVMAPPER_H__
+
+int
+virDevMapperGetTargets(const char *path,
+                       char ***devPaths);
+
+#endif /* __VIR_DEVMAPPER_H__ */