Add zfs module feature and property info to sysfs

This extends our sysfs '/sys/module/zfs' entry to include feature 
and property attributes. The primary consumer of this information 
is user processes, like the zfs CLI, that need to know what the 
current loaded ZFS module supports. The libzfs binary will consult 
this information when instantiating the zfs and zpool property 
tables and the pool features table.

This introduces 4 kernel objects (dirs) into '/sys/module/zfs'
with corresponding attributes (files):
  features.runtime
  features.pool
  properties.dataset
  properties.pool

Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Don Brady <don.brady@delphix.com>
Closes #7706

module/zcommon/zfeature_common.c

@@ -29,11 +29,13 @@
 #ifndef _KERNEL
 #include <errno.h>
 #include <string.h>
+#include <sys/stat.h>
 #endif
 #include <sys/debug.h>
 #include <sys/fs/zfs.h>
 #include <sys/inttypes.h>
 #include <sys/types.h>
+#include <sys/zfs_sysfs.h>
 #include "zfeature_common.h"
 
 /*
@@ -100,11 +102,30 @@ zfeature_is_supported(const char *guid)
 	return (B_FALSE);
 }
 
+int
+zfeature_lookup_guid(const char *guid, spa_feature_t *res)
+{
+	for (spa_feature_t i = 0; i < SPA_FEATURES; i++) {
+		zfeature_info_t *feature = &spa_feature_table[i];
+		if (!feature->fi_zfs_mod_supported)
+			continue;
+		if (strcmp(guid, feature->fi_guid) == 0) {
+			if (res != NULL)
+				*res = i;
+			return (0);
+		}
+	}
+
+	return (ENOENT);
+}
+
 int
 zfeature_lookup_name(const char *name, spa_feature_t *res)
 {
 	for (spa_feature_t i = 0; i < SPA_FEATURES; i++) {
 		zfeature_info_t *feature = &spa_feature_table[i];
+		if (!feature->fi_zfs_mod_supported)
+			continue;
 		if (strcmp(name, feature->fi_uname) == 0) {
 			if (res != NULL)
 				*res = i;
@@ -137,6 +158,34 @@ deps_contains_feature(const spa_feature_t *deps, const spa_feature_t feature)
 	return (B_FALSE);
 }
 
+static boolean_t
+zfs_mod_supported_feature(const char *name)
+{
+	/*
+	 * The zfs module spa_feature_table[], whether in-kernel or in
+	 * libzpool, always supports all the features. libzfs needs to
+	 * query the running module, via sysfs, to determine which
+	 * features are supported.
+	 */
+#if defined(_KERNEL) || defined(LIB_ZPOOL_BUILD)
+	return (B_TRUE);
+#else
+	struct stat64 statbuf;
+	char *path;
+	boolean_t supported = B_FALSE;
+	int len;
+
+	len = asprintf(&path, "%s/%s/%s", ZFS_SYSFS_DIR,
+	    ZFS_SYSFS_POOL_FEATURES, name);
+
+	if (len > 0) {
+		supported = !!(stat64(path, &statbuf) == 0);
+		free(path);
+	}
+	return (supported);
+#endif
+}
+
 static void
 zfeature_register(spa_feature_t fid, const char *guid, const char *name,
     const char *desc, zfeature_flags_t flags, const spa_feature_t *deps)
@@ -163,6 +212,7 @@ zfeature_register(spa_feature_t fid, const char *guid, const char *name,
 	feature->fi_desc = desc;
 	feature->fi_flags = flags;
 	feature->fi_depends = deps;
+	feature->fi_zfs_mod_supported = zfs_mod_supported_feature(guid);
 }
 
 void
@@ -361,6 +411,7 @@ zpool_feature_init(void)
 }
 
 #if defined(_KERNEL)
+EXPORT_SYMBOL(zfeature_lookup_guid);
 EXPORT_SYMBOL(zfeature_lookup_name);
 EXPORT_SYMBOL(zfeature_is_supported);
 EXPORT_SYMBOL(zfeature_is_valid_guid);

module/zcommon/zfs_prop.c

@@ -720,7 +720,8 @@ zfs_prop_readonly(zfs_prop_t prop)
 boolean_t
 zfs_prop_visible(zfs_prop_t prop)
 {
-	return (zfs_prop_table[prop].pd_visible);
+	return (zfs_prop_table[prop].pd_visible &&
+	    zfs_prop_table[prop].pd_zfs_mod_supported);
 }
 
 /*

module/zcommon/zprop_common.c

@@ -34,6 +34,7 @@
 #include <sys/spa.h>
 #include <sys/zfs_acl.h>
 #include <sys/zfs_ioctl.h>
+#include <sys/zfs_sysfs.h>
 #include <sys/zfs_znode.h>
 #include <sys/fs/zfs.h>
 
@@ -48,6 +49,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <ctype.h>
+#include <sys/stat.h>
 #endif
 
 static zprop_desc_t *
@@ -68,6 +70,34 @@ zprop_get_numprops(zfs_type_t type)
 		return (ZFS_NUM_PROPS);
 }
 
+static boolean_t
+zfs_mod_supported_prop(const char *name, zfs_type_t type)
+{
+/*
+ * The zfs module spa_feature_table[], whether in-kernel or in libzpool,
+ * always supports all the properties. libzfs needs to query the running
+ * module, via sysfs, to determine which properties are supported.
+ */
+#if defined(_KERNEL) || defined(LIB_ZPOOL_BUILD)
+	return (B_TRUE);
+#else
+	struct stat64 statbuf;
+	char *path;
+	boolean_t supported = B_FALSE;
+	int len;
+
+	len = asprintf(&path, "%s/%s/%s", ZFS_SYSFS_DIR,
+	    (type == ZFS_TYPE_POOL) ? ZFS_SYSFS_POOL_PROPERTIES :
+	    ZFS_SYSFS_DATASET_PROPERTIES, name);
+
+	if (len > 0) {
+		supported = !!(stat64(path, &statbuf) == 0);
+		free(path);
+	}
+	return (supported);
+#endif
+}
+
 void
 zprop_register_impl(int prop, const char *name, zprop_type_t type,
     uint64_t numdefault, const char *strdefault, zprop_attr_t attr,
@@ -94,6 +124,7 @@ zprop_register_impl(int prop, const char *name, zprop_type_t type,
 	pd->pd_colname = colname;
 	pd->pd_rightalign = rightalign;
 	pd->pd_visible = visible;
+	pd->pd_zfs_mod_supported = zfs_mod_supported_prop(name, objset_types);
 	pd->pd_table = idx_tbl;
 	pd->pd_table_size = 0;
 	while (idx_tbl && (idx_tbl++)->pi_name != NULL)
@@ -193,6 +224,7 @@ zprop_iter_common(zprop_func func, void *cb, boolean_t show_all,
 	prop = ZPROP_CONT;
 	for (i = 0; i < num_props; i++) {
 		if ((order[i]->pd_visible || show_all) &&
+		    order[i]->pd_zfs_mod_supported &&
 		    (func(order[i]->pd_propnum, cb) != ZPROP_CONT)) {
 			prop = order[i]->pd_propnum;
 			break;