On Tue, Apr 03, 2018 at 11:03:25 +0200, Michal Privoznik wrote:
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 | 4 + src/util/Makefile.inc.am | 2 + src/util/virdevmapper.c | 200 +++++++++++++++++++++++++++++++++++++++++++++++ src/util/virdevmapper.h | 31 ++++++++ 4 files changed, 237 insertions(+) create mode 100644 src/util/virdevmapper.c create mode 100644 src/util/virdevmapper.h
[...]
diff --git a/src/util/virdevmapper.c b/src/util/virdevmapper.c new file mode 100644 index 0000000000..9491848f48 --- /dev/null +++ b/src/util/virdevmapper.c @@ -0,0 +1,200 @@ +/* + * virdevmapper.c: Functions for handling devmapper
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>
[...]
+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) {
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) {
So these report libvirt errors, but don't mess them up. And only in case of OOM, so this is fine.
+ 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 = 4;
So even trivial setups (dmcrypt + LVM) would exhaust half of your limit for the device mapper block devices, and would still recurse one more level to check the backing block device. I think we need some more headroom here. I'd go with 16 or 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. My dice chose + * four. */
Drop the last sentence of this comment.
+ + return virDevMapperGetTargetsImpl(path, devPaths, ttl); +} +
ACK if you fix the condition syntax, raise the recursion level significantly, and tweak the comment.