module/*.ko: prune .data, global .rodata

Evaluated every variable that lives in .data (and globals in .rodata)
in the kernel modules, and constified/eliminated/localised them
appropriately. This means that all read-only data is now actually
read-only data, and, if possible, at file scope. A lot of previously-
global-symbols became inlinable (and inlined!) constants. Probably
not in a big Wowee Performance Moment, but hey.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #12899

module/zcommon/zfeature_common.c

@@ -325,7 +325,7 @@ zfeature_register(spa_feature_t fid, const char *guid, const char *name,
     const struct zfs_mod_supported_features *sfeatures)
 {
 	zfeature_info_t *feature = &spa_feature_table[fid];
-	static spa_feature_t nodeps[] = { SPA_FEATURE_NONE };
+	static const spa_feature_t nodeps[] = { SPA_FEATURE_NONE };
 
 	ASSERT(name != NULL);
 	ASSERT(desc != NULL);

module/zcommon/zfs_comutil.c

@@ -158,13 +158,11 @@ static zfs_version_spa_map_t zfs_version_table[] = {
 int
 zfs_zpl_version_map(int spa_version)
 {
-	int i;
 	int version = -1;
 
-	for (i = 0; zfs_version_table[i].version_spa; i++) {
+	for (int i = 0; zfs_version_table[i].version_spa; i++)
 		if (spa_version >= zfs_version_table[i].version_spa)
 			version = zfs_version_table[i].version_zpl;
-	}
 
 	return (version);
 }
@@ -176,22 +174,18 @@ zfs_zpl_version_map(int spa_version)
 int
 zfs_spa_version_map(int zpl_version)
 {
-	int i;
-	int version = -1;
-
-	for (i = 0; zfs_version_table[i].version_zpl; i++) {
+	for (int i = 0; zfs_version_table[i].version_zpl; i++)
 		if (zfs_version_table[i].version_zpl >= zpl_version)
 			return (zfs_version_table[i].version_spa);
-	}
 
-	return (version);
+	return (-1);
 }
 
 /*
  * This is the table of legacy internal event names; it should not be modified.
  * The internal events are now stored in the history log as strings.
  */
-const char *zfs_history_event_names[ZFS_NUM_LEGACY_HISTORY_EVENTS] = {
+const char *const zfs_history_event_names[ZFS_NUM_LEGACY_HISTORY_EVENTS] = {
 	"invalid event",
 	"pool create",
 	"vdev add",
@@ -243,9 +237,7 @@ zfs_dataset_name_hidden(const char *name)
 	 * internal datasets (which have a $ in their name), and
 	 * temporary datasets (which have a % in their name).
 	 */
-	if (strchr(name, '$') != NULL)
-		return (B_TRUE);
-	if (strchr(name, '%') != NULL)
+	if (strpbrk(name, "$%") != NULL)
 		return (B_TRUE);
 	if (!INGLOBALZONE(curproc) && !zone_dataset_visible(name, NULL))
 		return (B_TRUE);

module/zcommon/zfs_deleg.c

@@ -42,7 +42,7 @@
 #include "zfs_deleg.h"
 #include "zfs_namecheck.h"
 
-zfs_deleg_perm_tab_t zfs_deleg_perm_tab[] = {
+const zfs_deleg_perm_tab_t zfs_deleg_perm_tab[] = {
 	{ZFS_DELEG_PERM_ALLOW},
 	{ZFS_DELEG_PERM_BOOKMARK},
 	{ZFS_DELEG_PERM_CLONE},
@@ -89,15 +89,12 @@ zfs_valid_permission_name(const char *perm)
 const char *
 zfs_deleg_canonicalize_perm(const char *perm)
 {
-	int i;
-	zfs_prop_t prop;
-
-	for (i = 0; zfs_deleg_perm_tab[i].z_perm != NULL; i++) {
+	for (int i = 0; zfs_deleg_perm_tab[i].z_perm != NULL; i++) {
 		if (strcmp(perm, zfs_deleg_perm_tab[i].z_perm) == 0)
 			return (perm);
 	}
 
-	prop = zfs_name_to_prop(perm);
+	zfs_prop_t prop = zfs_name_to_prop(perm);
 	if (prop != ZPROP_INVAL && zfs_prop_delegatable(prop))
 		return (zfs_prop_to_name(prop));
 	return (NULL);

module/zcommon/zfs_prop.c

@@ -50,7 +50,7 @@
 static zprop_desc_t zfs_prop_table[ZFS_NUM_PROPS];
 
 /* Note this is indexed by zfs_userquota_prop_t, keep the order the same */
-const char *zfs_userquota_prop_prefixes[] = {
+const char *const zfs_userquota_prop_prefixes[] = {
 	"userused@",
 	"userquota@",
 	"groupused@",