[v2,16/49] libmultipath: add cleanup_dm_task(), and use it in devmapper.c

Message ID	20240712171458.77611-17-mwilck@suse.com (mailing list archive)
State	Not Applicable, archived
Delegated to:	christophe varoqui
Headers	show Received: from mail-ed1-f51.google.com (mail-ed1-f51.google.com [209.85.208.51]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6817F175564 for <dm-devel@lists.linux.dev>; Fri, 12 Jul 2024 17:15:48 +0000 (UTC) From: Martin Wilck <martin.wilck@suse.com> To: Christophe Varoqui <christophe.varoqui@opensvc.com>, Benjamin Marzinski <bmarzins@redhat.com> Cc: dm-devel@lists.linux.dev, Martin Wilck <mwilck@suse.com> Subject: [PATCH v2 16/49] libmultipath: add cleanup_dm_task(), and use it in devmapper.c Date: Fri, 12 Jul 2024 19:14:24 +0200 Message-ID: <20240712171458.77611-17-mwilck@suse.com> In-Reply-To: <20240712171458.77611-1-mwilck@suse.com> References: <20240712171458.77611-1-mwilck@suse.com> Precedence: bulk MIME-Version: 1.0 Content-Transfer-Encoding: 8bit
Series	multipath-tools: devmapper API refactored \| expand [v2,00/49] multipath-tools: devmapper API refactored [v2,01/49] multipath-tools CI: more fixes for arm/v7 [v2,02/49] multipath-tools CI: fix dmevents test for Debian Sid, arm/v7 [v2,03/49] create-config.mk: use printf instead of /bin/echo [v2,04/49] multipathd.service.in: use @BINDIR@ instead of /sbin [v2,05/49] Makefile.inc: replace @BINDIR@ with $(TGTDIR)/$(bindir) [v2,06/49] kpartx.rules: use @BINDIR@ to locate kpartx [v2,07/49] multipath-tools: Remove hard-coded paths to executables [v2,08/49] multipath-tools: compile_commands.json fixes [v2,09/49] multipath-tools: .gitignore: ignore o.wrap files for CI helpers [v2,10/49] libmultipath: remove unused includes in devmapper.h [v2,11/49] libmultipath: use DM_DEVICE_INFO in dm_mapname() [v2,12/49] multipath-tools: don't call dm_task_no_open_count() [v2,13/49] libmpathutil: export cleanup_udev_device() [v2,14/49] libmpathutil: add cleanup_vector() [v2,15/49] libmultipath: add cleanup helpers for struct multipath [v2,16/49] libmultipath: add cleanup_dm_task(), and use it in devmapper.c [v2,17/49] libmultipath: rename dm_type()->dm_type_match() and use symbolic values [v2,18/49] libmultipath: Use symbolic return values for dm_is_mpath() [v2,19/49] libmultipath: add libmp_mapinfo() [v2,20/49] libmultipath tests: add tests for libmp_mapinfo() [v2,21/49] libmultipath: implement dm_get_info() and dm_map_present() with new API [v2,22/49] libmultipath: remove dm_get_prefixed_uuid() [v2,23/49] libmultipath: is_mpath_part(): improve parsing [v2,24/49] libmultipath: rename dm_get_uuid() -> dm_get_wwid() [v2,25/49] libmultipath: improve dm_get_wwid() return value logic [v2,26/49] libmultipath: reimplement dm_map_name() with new API [v2,27/49] libmultipath: reimplement dm_map_present_by_uuid() [v2,28/49] libmultipath: reimplement dm_get_opencount() with new API [v2,29/49] libmpathpersist: skip redundant dm_map_present() call [v2,30/49] libmultipath: implement dm_is_mpath() with new API [v2,31/49] libmultipath: implement dm_get_multipath() with new API [v2,32/49] libmultipath: use libmp_mapinfo() in _dm_flush_map() [v2,33/49] libmultipath: add is_mpath_uuid() helper [v2,34/49] libmultipath: add is_mpath_part_uuid() helper [v2,35/49] libmultipath: add dmp_errstr() helper [v2,36/49] libmultipath: use libmp_mapinfo() in do_foreach_partmaps() [v2,37/49] libmultipath: use libmp_pathinfo() in update_multipath_table() [v2,38/49] libmultipath: update mpp->dmi in update_multipath_table() [v2,39/49] libmultipath: drop extra call to dm_map_present() in domap() [v2,40/49] libmultipath: split off update_multipath_table__() [v2,41/49] multipath: implement check_usable_paths() with libmp_pathinfo() [v2,42/49] multipathd: implement add_map_without_path() with libmp_mapinfo() [v2,43/49] libmultipath: simplify dm_get_maps() [v2,44/49] libmpathpersist: use libmp_mapinfo() in mpath_get_map() [v2,45/49] libmpathpersist: use mpp->alias in do_mpath_persistent_reserve_out() [v2,46/49] libmultipath: fix deferred_remove logic in remove_partmap() [v2,47/49] libmultipath: don't call do_foreach_partmaps() recursively [v2,48/49] libmultipath: Move UUID check into libmp_pathinfo__() [v2,49/49] multipath-tools tests: fix directio test with real device

diff --git a/libmultipath/devmapper.c b/libmultipath/devmapper.c index 8996c1d..4bff62d 100644 --- a/libmultipath/devmapper.c +++ b/libmultipath/devmapper.c @@ -91,6 +91,12 @@ int libmp_dm_task_run(struct dm_task *dmt) return r; } +static void cleanup_dm_task(struct dm_task **pdmt) +{ + if (*pdmt) + dm_task_destroy(*pdmt); +} + __attribute__((format(printf, 4, 5))) static void dm_write_log (int level, const char *file, int line, const char *f, ...) { @@ -203,8 +209,8 @@ static void init_dm_drv_version(void) static int dm_tgt_version (unsigned int *version, char *str) { - int r = 2; - struct dm_task *dmt; + bool found = false; + struct dm_task __attribute__((cleanup(cleanup_dm_task))) *dmt = NULL; struct dm_versions *target; struct dm_versions *last_target; unsigned int *v; @@ -220,31 +226,28 @@ static int dm_tgt_version (unsigned int *version, char *str) if (!libmp_dm_task_run(dmt)) { dm_log_error(2, DM_DEVICE_LIST_VERSIONS, dmt); condlog(0, "Cannot communicate with kernel DM"); - goto out; + return 1; } target = dm_task_get_versions(dmt); do { last_target = target; if (!strncmp(str, target->name, strlen(str))) { - r = 1; + found = true; break; } target = (void *) target + target->next; } while (last_target != target); - if (r == 2) { + if (!found) { condlog(0, "DM %s kernel driver not loaded", str); - goto out; + return 1; } v = target->version; version[0] = v[0]; version[1] = v[1]; version[2] = v[2]; - r = 0; -out: - dm_task_destroy(dmt); - return r; + return 0; } static void init_dm_mpath_version(void) @@ -383,18 +386,18 @@ libmp_dm_task_create(int task) static int dm_simplecmd (int task, const char *name, int flags, uint16_t udev_flags) { - int r = 0; + int r; int udev_wait_flag = (((flags & DMFL_NEED_SYNC) || udev_flags) && (task == DM_DEVICE_RESUME || task == DM_DEVICE_REMOVE)); uint32_t cookie = 0; - struct dm_task *dmt; + struct dm_task __attribute__((cleanup(cleanup_dm_task))) *dmt = NULL; if (!(dmt = libmp_dm_task_create (task))) return 0; if (!dm_task_set_name (dmt, name)) - goto out; + return 0; dm_task_skip_lockfs(dmt); /* for DM_DEVICE_RESUME */ #ifdef LIBDM_API_FLUSH @@ -408,7 +411,7 @@ dm_simplecmd (int task, const char *name, int flags, uint16_t udev_flags) { if (udev_wait_flag && !dm_task_set_cookie(dmt, &cookie, DM_UDEV_DISABLE_LIBRARY_FALLBACK | udev_flags)) - goto out; + return 0; r = libmp_dm_task_run (dmt); if (!r) @@ -416,8 +419,6 @@ dm_simplecmd (int task, const char *name, int flags, uint16_t udev_flags) { if (udev_wait_flag) libmp_udev_wait(cookie); -out: - dm_task_destroy (dmt); return r; } @@ -440,8 +441,9 @@ static int dm_addmap (int task, const char *target, struct multipath *mpp, char * params, int ro, uint16_t udev_flags) { int r = 0; - struct dm_task *dmt; - char *prefixed_uuid = NULL; + struct dm_task __attribute__((cleanup(cleanup_dm_task))) *dmt = NULL; + char __attribute__((cleanup(cleanup_charp))) *prefixed_uuid = NULL; + uint32_t cookie = 0; if (task == DM_DEVICE_CREATE && strlen(mpp->wwid) == 0) { @@ -457,10 +459,10 @@ dm_addmap (int task, const char *target, struct multipath *mpp, return 0; if (!dm_task_set_name (dmt, mpp->alias)) - goto addout; + return 0; if (!dm_task_add_target (dmt, 0, mpp->size, target, params)) - goto addout; + return 0; if (ro) dm_task_set_ro(dmt); @@ -469,10 +471,10 @@ dm_addmap (int task, const char *target, struct multipath *mpp, if (asprintf(&prefixed_uuid, UUID_PREFIX "%s", mpp->wwid) < 0) { condlog(0, "cannot create prefixed uuid : %s", strerror(errno)); - goto addout; + return 0; } if (!dm_task_set_uuid(dmt, prefixed_uuid)) - goto freeout; + return 0; dm_task_skip_lockfs(dmt); #ifdef LIBDM_API_FLUSH dm_task_no_flush(dmt); @@ -481,33 +483,28 @@ dm_addmap (int task, const char *target, struct multipath *mpp, if (mpp->attribute_flags & (1 << ATTR_MODE) && !dm_task_set_mode(dmt, mpp->mode)) - goto freeout; + return 0; if (mpp->attribute_flags & (1 << ATTR_UID) && !dm_task_set_uid(dmt, mpp->uid)) - goto freeout; + return 0; if (mpp->attribute_flags & (1 << ATTR_GID) && !dm_task_set_gid(dmt, mpp->gid)) - goto freeout; + return 0; + condlog(2, "%s: %s [0 %llu %s %s]", mpp->alias, task == DM_DEVICE_RELOAD ? "reload" : "addmap", mpp->size, target, params); if (task == DM_DEVICE_CREATE && !dm_task_set_cookie(dmt, &cookie, udev_flags)) - goto freeout; + return 0; r = libmp_dm_task_run (dmt); if (!r) dm_log_error(2, task, dmt); if (task == DM_DEVICE_CREATE) - libmp_udev_wait(cookie); -freeout: - if (prefixed_uuid) - free(prefixed_uuid); - -addout: - dm_task_destroy (dmt); + libmp_udev_wait(cookie); if (r) mpp->need_reload = false; @@ -648,46 +645,41 @@ int dm_map_present(const char * str) int dm_get_map(const char *name, unsigned long long *size, char **outparams) { - int r = DMP_ERR; - struct dm_task *dmt; + struct dm_task __attribute__((cleanup(cleanup_dm_task))) *dmt = NULL; uint64_t start, length; char *target_type = NULL; char *params = NULL; if (!(dmt = libmp_dm_task_create(DM_DEVICE_TABLE))) - return r; + return DMP_ERR; if (!dm_task_set_name(dmt, name)) - goto out; + return DMP_ERR; errno = 0; if (!libmp_dm_task_run(dmt)) { dm_log_error(3, DM_DEVICE_TABLE, dmt); if (dm_task_get_errno(dmt) == ENXIO) - r = DMP_NOT_FOUND; - goto out; + return DMP_NOT_FOUND; + else + return DMP_ERR; } - r = DMP_NOT_FOUND; /* Fetch 1st target */ if (dm_get_next_target(dmt, NULL, &start, &length, &target_type, &params) != NULL || !params) /* more than one target or not found target */ - goto out; + return DMP_NOT_FOUND; if (size) *size = length; if (!outparams) - r = DMP_OK; + return DMP_OK; else { *outparams = strdup(params); - r = *outparams ? DMP_OK : DMP_ERR; + return *outparams ? DMP_OK : DMP_ERR; } - -out: - dm_task_destroy(dmt); - return r; } static int @@ -767,7 +759,7 @@ is_mpath_part(const char *part_name, const char *map_name) int dm_get_status(const char *name, char **outstatus) { int r = DMP_ERR; - struct dm_task *dmt; + struct dm_task __attribute__((cleanup(cleanup_dm_task))) *dmt = NULL; uint64_t start, length; char *target_type = NULL; char *status = NULL; @@ -796,7 +788,7 @@ int dm_get_status(const char *name, char **outstatus) goto out; if (!status) { - condlog(2, "get null status."); + condlog(2, "got null status."); goto out; } @@ -808,9 +800,9 @@ int dm_get_status(const char *name, char **outstatus) } out: if (r != DMP_OK) - condlog(0, "%s: error getting map status string", name); + condlog(0, "%s: %s: error getting map status string: %d", + __func__, name, r); - dm_task_destroy(dmt); return r; } @@ -823,7 +815,7 @@ out: int dm_type(const char *name, char *type) { int r = 0; - struct dm_task *dmt; + struct dm_task __attribute__((cleanup(cleanup_dm_task))) *dmt = NULL; uint64_t start, length; char *target_type = NULL; char *params; @@ -850,7 +842,6 @@ int dm_type(const char *name, char *type) r = 1; out: - dm_task_destroy(dmt); return r; } @@ -863,7 +854,7 @@ out: int dm_is_mpath(const char *name) { int r = -1; - struct dm_task *dmt; + struct dm_task __attribute__((cleanup(cleanup_dm_task))) *dmt = NULL; struct dm_info info; uint64_t start, length; char *target_type = NULL; @@ -874,38 +865,36 @@ int dm_is_mpath(const char *name) goto out; if (!dm_task_set_name(dmt, name)) - goto out_task; + goto out; if (!libmp_dm_task_run(dmt)) { dm_log_error(3, DM_DEVICE_TABLE, dmt); - goto out_task; + goto out; } if (!dm_task_get_info(dmt, &info)) - goto out_task; + goto out; r = 0; if (!info.exists) - goto out_task; + goto out; uuid = dm_task_get_uuid(dmt); if (!uuid || strncmp(uuid, UUID_PREFIX, UUID_PREFIX_LEN) != 0) - goto out_task; + goto out; /* Fetch 1st target */ if (dm_get_next_target(dmt, NULL, &start, &length, &target_type, &params) != NULL) /* multiple targets */ - goto out_task; + goto out; if (!target_type || strcmp(target_type, TGT_MPATH) != 0) - goto out_task; + goto out; r = 1; -out_task: - dm_task_destroy(dmt); out: if (r < 0) condlog(3, "%s: dm command failed in %s: %s", name, __FUNCTION__, strerror(errno)); @@ -1131,10 +1120,10 @@ dm_flush_map_nopaths(const char *mapname, int deferred_remove __DR_UNUSED__) return _dm_flush_map(mapname, flags, 0); } -int dm_flush_maps (int retries) +int dm_flush_maps(int retries) { int r = DM_FLUSH_FAIL; - struct dm_task *dmt; + struct dm_task __attribute__((cleanup(cleanup_dm_task))) *dmt = NULL; struct dm_names *names; unsigned next = 0; @@ -1143,15 +1132,15 @@ int dm_flush_maps (int retries) if (!libmp_dm_task_run (dmt)) { dm_log_error(3, DM_DEVICE_LIST, dmt); - goto out; + return r; } if (!(names = dm_task_get_names (dmt))) - goto out; + return r; r = DM_FLUSH_OK; if (!names->dev) - goto out; + return r; do { int ret; @@ -1163,16 +1152,13 @@ int dm_flush_maps (int retries) names = (void *) names + next; } while (next); -out: - dm_task_destroy (dmt); return r; } int dm_message(const char * mapname, char * message) { - int r = 1; - struct dm_task *dmt; + struct dm_task __attribute__((cleanup(cleanup_dm_task))) *dmt = NULL; if (!(dmt = libmp_dm_task_create(DM_DEVICE_TARGET_MSG))) return 1; @@ -1191,13 +1177,10 @@ dm_message(const char * mapname, char * message) goto out; } - r = 0; + return 0; out: - if (r) - condlog(0, "DM message failed [%s]", message); - - dm_task_destroy(dmt); - return r; + condlog(0, "DM message failed [%s]", message); + return 1; } int @@ -1305,12 +1288,10 @@ out: return NULL; } -int -dm_get_maps (vector mp) +int dm_get_maps(vector mp) { struct multipath * mpp; - int r = 1; - struct dm_task *dmt; + struct dm_task __attribute__((cleanup(cleanup_dm_task))) *dmt = NULL; struct dm_names *names; unsigned next = 0; @@ -1322,15 +1303,15 @@ dm_get_maps (vector mp) if (!libmp_dm_task_run(dmt)) { dm_log_error(3, DM_DEVICE_LIST, dmt); - goto out; + return 1; } if (!(names = dm_task_get_names(dmt))) - goto out; + return 1; if (!names->dev) { - r = 0; /* this is perfectly valid */ - goto out; + /* this is perfectly valid */ + return 0; } do { @@ -1339,11 +1320,11 @@ dm_get_maps (vector mp) mpp = dm_get_multipath(names->name); if (!mpp) - goto out; + return 1; if (!vector_alloc_slot(mp)) { free_multipath(mpp, KEEP_PATHS); - goto out; + return 1; } vector_set_slot(mp, mpp); @@ -1352,11 +1333,7 @@ next: names = (void *) names + next; } while (next); - r = 0; - goto out; -out: - dm_task_destroy (dmt); - return r; + return 0; } int @@ -1419,10 +1396,10 @@ do_foreach_partmaps (const char * mapname, int (*partmap_func)(const char *, void *), void *data) { - struct dm_task *dmt; + struct dm_task __attribute__((cleanup(cleanup_dm_task))) *dmt = NULL; + char __attribute__((cleanup(cleanup_charp))) *params = NULL; struct dm_names *names; unsigned next = 0; - char *params = NULL; unsigned long long size; char dev_t[32]; int r = 1; @@ -1431,21 +1408,18 @@ do_foreach_partmaps (const char * mapname, if (!(dmt = libmp_dm_task_create(DM_DEVICE_LIST))) return 1; - if (!libmp_dm_task_run(dmt)) { - dm_log_error(3, DM_DEVICE_LIST, dmt); - goto out; - } + if (!libmp_dm_task_run(dmt)) + return 1; if (!(names = dm_task_get_names(dmt))) - goto out; + return 1; - if (!names->dev) { - r = 0; /* this is perfectly valid */ - goto out; - } + if (!names->dev) + /* this is perfectly valid */ + return 0; if (dm_dev_t(mapname, &dev_t[0], 32)) - goto out; + return 1; do { if ( @@ -1472,7 +1446,7 @@ do_foreach_partmaps (const char * mapname, !isdigit(*(p + strlen(dev_t))) ) { if ((r = partmap_func(names->name, data)) != 0) - goto out; + return 1; } free(params); @@ -1481,11 +1455,7 @@ do_foreach_partmaps (const char * mapname, names = (void *) names + next; } while (next); - r = 0; -out: - free(params); - dm_task_destroy (dmt); - return r; + return 0; } struct remove_data { @@ -1623,7 +1593,7 @@ int dm_rename (const char * old, char * new, char *delim, int skip_kpartx) { int r = 0; - struct dm_task *dmt; + struct dm_task __attribute__((cleanup(cleanup_dm_task))) *dmt = NULL; uint32_t cookie = 0; uint16_t udev_flags = DM_UDEV_DISABLE_LIBRARY_FALLBACK | ((skip_kpartx == SKIP_KPARTX_ON)? MPATH_UDEV_NO_KPARTX_FLAG : 0); @@ -1634,22 +1604,19 @@ dm_rename (const char * old, char * new, char *delim, int skip_kpartx) return r; if (!dm_task_set_name(dmt, old)) - goto out; + return r; if (!dm_task_set_newname(dmt, new)) - goto out; + return r; if (!dm_task_set_cookie(dmt, &cookie, udev_flags)) - goto out; + return r; + r = libmp_dm_task_run(dmt); if (!r) dm_log_error(2, DM_DEVICE_RENAME, dmt); libmp_udev_wait(cookie); - -out: - dm_task_destroy(dmt); - return r; } @@ -1672,9 +1639,10 @@ void dm_reassign_deps(char *table, const char *dep, const char *newdep) int dm_reassign_table(const char *name, char *old, char *new) { - int r = 0, modified = 0; + int modified = 0; uint64_t start, length; - struct dm_task *dmt, *reload_dmt; + struct dm_task __attribute__((cleanup(cleanup_dm_task))) *dmt = NULL; + struct dm_task __attribute__((cleanup(cleanup_dm_task))) *reload_dmt = NULL; char *target, *params = NULL; char *buff; void *next = NULL; @@ -1683,16 +1651,16 @@ int dm_reassign_table(const char *name, char *old, char *new) return 0; if (!dm_task_set_name(dmt, name)) - goto out; + return 0; if (!libmp_dm_task_run(dmt)) { dm_log_error(3, DM_DEVICE_TABLE, dmt); - goto out; + return 0; } if (!(reload_dmt = libmp_dm_task_create(DM_DEVICE_RELOAD))) - goto out; + return 0; if (!dm_task_set_name(reload_dmt, name)) - goto out_reload; + return 0; do { next = dm_get_next_target(dmt, next, &start, &length, @@ -1705,13 +1673,13 @@ int dm_reassign_table(const char *name, char *old, char *new) */ condlog(1, "%s: invalid target found in map %s", __func__, name); - goto out_reload; + return 0; } buff = strdup(params); if (!buff) { condlog(3, "%s: failed to replace target %s, " "out of memory", name, target); - goto out_reload; + return 0; } if (strcmp(target, TGT_MPATH) && strstr(params, old)) { condlog(3, "%s: replace target %s %s", @@ -1729,18 +1697,12 @@ int dm_reassign_table(const char *name, char *old, char *new) if (!libmp_dm_task_run(reload_dmt)) { dm_log_error(3, DM_DEVICE_RELOAD, reload_dmt); condlog(3, "%s: failed to reassign targets", name); - goto out_reload; + return 0; } dm_simplecmd_noflush(DM_DEVICE_RESUME, name, MPATH_UDEV_RELOAD_FLAG); } - r = 1; - -out_reload: - dm_task_destroy(reload_dmt); -out: - dm_task_destroy(dmt); - return r; + return 1; } @@ -1752,10 +1714,9 @@ out: int dm_reassign(const char *mapname) { struct dm_deps *deps; - struct dm_task *dmt; + struct dm_task __attribute__((cleanup(cleanup_dm_task))) *dmt = NULL; struct dm_info info; char dev_t[32], dm_dep[32]; - int r = 0; unsigned int i; if (dm_dev_t(mapname, &dev_t[0], 32)) { @@ -1769,21 +1730,21 @@ int dm_reassign(const char *mapname) } if (!dm_task_set_name(dmt, mapname)) - goto out; + return 0; if (!libmp_dm_task_run(dmt)) { dm_log_error(3, DM_DEVICE_DEPS, dmt); - goto out; + return 0; } if (!dm_task_get_info(dmt, &info)) - goto out; + return 0; if (!(deps = dm_task_get_deps(dmt))) - goto out; + return 0; if (!info.exists) - goto out; + return 0; for (i = 0; i < deps->count; i++) { sprintf(dm_dep, "%d:%d", @@ -1792,15 +1753,12 @@ int dm_reassign(const char *mapname) sysfs_check_holders(dm_dep, dev_t); } - r = 1; -out: - dm_task_destroy (dmt); - return r; + return 1; } int dm_setgeometry(struct multipath *mpp) { - struct dm_task *dmt; + struct dm_task __attribute__((cleanup(cleanup_dm_task))) *dmt = NULL; struct path *pp; char heads[4], sectors[4]; char cylinders[10], start[32]; @@ -1825,7 +1783,7 @@ int dm_setgeometry(struct multipath *mpp) return 0; if (!dm_task_set_name(dmt, mpp->alias)) - goto out; + return 0; /* What a sick interface ... */ snprintf(heads, 4, "%u", pp->geom.heads); @@ -1834,14 +1792,12 @@ int dm_setgeometry(struct multipath *mpp) snprintf(start, 32, "%lu", pp->geom.start); if (!dm_task_set_geometry(dmt, cylinders, heads, sectors, start)) { condlog(3, "%s: Failed to set geometry", mpp->alias); - goto out; + return 0; } r = libmp_dm_task_run(dmt); if (!r) dm_log_error(3, DM_DEVICE_SET_GEOMETRY, dmt); -out: - dm_task_destroy(dmt); return r; }

[v2,16/49] libmultipath: add cleanup_dm_task(), and use it in devmapper.c

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