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 <[email protected]>
Reviewed-by: Tony Hutter <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Don Brady <[email protected]>
Closes #7706 

1 files changed, 51 insertions, 0 deletions

diff --git a/module/zcommon/zfeature_common.c b/module/zcommon/zfeature_common.c
index f5c98933c..e2b0fd511 100644
--- a/module/zcommon/zfeature_common.c
+++ b/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"
 
 /*
@@ -101,10 +103,29 @@ zfeature_is_supported(const char *guid)
 }
 
 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);