zdb: detect cachefile automatically otherwise force import

If a pool is created with the cache file located in a non-default 
path /etc/default/zpool.cache, removed, or the cachefile property 
is set to none, zdb fails to show the pool unless we specify the 
cache file or use the -e option. This PR automates this process.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Akash B <akash-b@hpe.com>
Signed-off-by: Ameer Hamza <ahamza@ixsystems.com>
Closes #16071

cmd/zdb/zdb.c

@@ -89,6 +89,7 @@
 
 #include <libnvpair.h>
 #include <libzutil.h>
+#include <libzfs_core.h>
 
 #include <libzdb.h>
 
@@ -8924,6 +8925,9 @@ main(int argc, char **argv)
 	boolean_t target_is_spa = B_TRUE, dataset_lookup = B_FALSE;
 	nvlist_t *cfg = NULL;
 	struct sigaction action;
+	boolean_t force_import = B_FALSE;
+	boolean_t config_path_console = B_FALSE;
+	char pbuf[MAXPATHLEN];
 
 	dprintf_setup(&argc, argv);
 
@@ -9094,6 +9098,7 @@ main(int argc, char **argv)
 			}
 			break;
 		case 'U':
+			config_path_console = B_TRUE;
 			spa_config_path = optarg;
 			if (spa_config_path[0] != '/') {
 				(void) fprintf(stderr,
@@ -9153,9 +9158,6 @@ main(int argc, char **argv)
 	 */
 	spa_mode_readable_spacemaps = B_TRUE;
 
-	kernel_init(SPA_MODE_READ);
-	kernel_init_done = B_TRUE;
-
 	if (dump_all)
 		verbose = MAX(verbose, 1);
 
@@ -9174,6 +9176,53 @@ main(int argc, char **argv)
 	if (argc < 2 && dump_opt['R'])
 		usage();
 
+	target = argv[0];
+
+	/*
+	 * Automate cachefile
+	 */
+	if (!spa_config_path_env && !config_path_console && target &&
+	    libzfs_core_init() == 0) {
+		char *pname = strdup(target);
+		const char *value;
+		nvlist_t *pnvl;
+		nvlist_t *vnvl;
+
+		if (strpbrk(pname, "/@") != NULL)
+			*strpbrk(pname, "/@") = '\0';
+
+		if (pname && lzc_get_props(pname, &pnvl) == 0) {
+			if (nvlist_lookup_nvlist(pnvl, "cachefile",
+			    &vnvl) == 0) {
+				value = fnvlist_lookup_string(vnvl,
+				    ZPROP_VALUE);
+			} else {
+				value = "-";
+			}
+			strlcpy(pbuf, value, sizeof (pbuf));
+			if (pbuf[0] != '\0') {
+				if (pbuf[0] == '/') {
+					if (access(pbuf, F_OK) == 0)
+						spa_config_path = pbuf;
+					else
+						force_import = B_TRUE;
+				} else if ((strcmp(pbuf, "-") == 0 &&
+				    access(ZPOOL_CACHE, F_OK) != 0) ||
+				    strcmp(pbuf, "none") == 0) {
+					force_import = B_TRUE;
+				}
+			}
+			nvlist_free(vnvl);
+		}
+
+		free(pname);
+		nvlist_free(pnvl);
+		libzfs_core_fini();
+	}
+
+	kernel_init(SPA_MODE_READ);
+	kernel_init_done = B_TRUE;
+
 	if (dump_opt['E']) {
 		if (argc != 1)
 			usage();
@@ -9210,7 +9259,6 @@ main(int argc, char **argv)
 		fatal("internal error: %s", strerror(ENOMEM));
 
 	error = 0;
-	target = argv[0];
 
 	if (strpbrk(target, "/@") != NULL) {
 		size_t targetlen;
@@ -9256,9 +9304,17 @@ main(int argc, char **argv)
 		target_pool = target;
 	}
 
-	if (dump_opt['e']) {
+	if (dump_opt['e'] || force_import) {
 		importargs_t args = { 0 };
 
+		/*
+		 * If path is not provided, search in /dev
+		 */
+		if (searchdirs == NULL) {
+			searchdirs = umem_alloc(sizeof (char *), UMEM_NOFAIL);
+			searchdirs[nsearch++] = (char *)ZFS_DEVDIR;
+		}
+
 		args.paths = nsearch;
 		args.path = searchdirs;
 		args.can_be_active = B_TRUE;

include/libzfs_core.h

@@ -77,6 +77,7 @@ _LIBZFS_CORE_H int lzc_snaprange_space(const char *, const char *, uint64_t *);
 _LIBZFS_CORE_H int lzc_hold(nvlist_t *, int, nvlist_t **);
 _LIBZFS_CORE_H int lzc_release(nvlist_t *, nvlist_t **);
 _LIBZFS_CORE_H int lzc_get_holds(const char *, nvlist_t **);
+_LIBZFS_CORE_H int lzc_get_props(const char *, nvlist_t **);
 
 enum lzc_send_flags {
 	LZC_SEND_FLAG_EMBED_DATA = 1 << 0,

lib/libzfs_core/libzfs_core.abi

@@ -168,6 +168,7 @@
     <elf-symbol name='lzc_get_bookmarks' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
     <elf-symbol name='lzc_get_bootenv' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
     <elf-symbol name='lzc_get_holds' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
+    <elf-symbol name='lzc_get_props' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
     <elf-symbol name='lzc_get_vdev_prop' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
     <elf-symbol name='lzc_hold' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
     <elf-symbol name='lzc_initialize' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
@@ -2694,6 +2695,11 @@
       <parameter type-id='857bb57e' name='holdsp'/>
       <return type-id='95e97e5e'/>
     </function-decl>
+    <function-decl name='lzc_get_props' mangled-name='lzc_get_props' visibility='default' binding='global' size-in-bits='64' elf-symbol-id='lzc_get_props'>
+      <parameter type-id='80f4b756' name='poolname'/>
+      <parameter type-id='857bb57e' name='props'/>
+      <return type-id='95e97e5e'/>
+    </function-decl>
     <function-decl name='lzc_send_wrapper' mangled-name='lzc_send_wrapper' visibility='default' binding='global' size-in-bits='64' elf-symbol-id='lzc_send_wrapper'>
       <parameter type-id='2e711a2a' name='func'/>
       <parameter type-id='95e97e5e' name='orig_fd'/>

lib/libzfs_core/libzfs_core.c

@@ -596,6 +596,12 @@ lzc_get_holds(const char *snapname, nvlist_t **holdsp)
 	return (lzc_ioctl(ZFS_IOC_GET_HOLDS, snapname, NULL, holdsp));
 }
 
+int
+lzc_get_props(const char *poolname, nvlist_t **props)
+{
+	return (lzc_ioctl(ZFS_IOC_POOL_GET_PROPS, poolname, NULL, props));
+}
+
 static unsigned int
 max_pipe_buffer(int infd)
 {