zcommon: pre-iterate over sysfs instead of statting every feature

If sufficient memory (<2K, realistically) is available, libzfs_init()
can be significantly shorted by iterating over the correct sysfs
directory before registrations, we can turn 168 stats into 15/18
syscalls (3 opens (6 if built in), 3 fstats, 6 getdentses, and 3
closes), a tenfoldish reduction; this is probably a bit faster, too.

The list is always optional, and registration functions (and one-off
users) can simply pass NULL, which will fall back to the previous
mechanism

Also, don't allocate in zfs_mod_supported_impl, and use use access()
instead of stat(), since existence is really what we care about

Also, fix pre-prop-checking compat in fallback for built-in ZFS

Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Tony Nguyen <[email protected]>
Signed-off-by: Ahelenia Ziemiańska <[email protected]>
Closes #12089 

1 files changed, 10 insertions, 5 deletions

diff --git a/include/zfs_prop.h b/include/zfs_prop.h
index 8014c757a..c7363f701 100644
--- a/include/zfs_prop.h
+++ b/include/zfs_prop.h
@@ -28,6 +28,7 @@
 
 #include <sys/fs/zfs.h>
 #include <sys/types.h>
+#include <sys/zfs_sysfs.h>
 
 #ifdef	__cplusplus
 extern "C" {
@@ -111,15 +112,19 @@ _ZFS_PROP_H zprop_desc_t *vdev_prop_get_table(void);
  */
 _ZFS_PROP_H void zprop_register_impl(int, const char *, zprop_type_t, uint64_t,
     const char *, zprop_attr_t, int, const char *, const char *,
-    boolean_t, boolean_t, const zprop_index_t *);
+    boolean_t, boolean_t, const zprop_index_t *,
+    const struct zfs_mod_supported_features *);
 _ZFS_PROP_H void zprop_register_string(int, const char *, const char *,
-    zprop_attr_t attr, int, const char *, const char *);
+    zprop_attr_t attr, int, const char *, const char *,
+    const struct zfs_mod_supported_features *);
 _ZFS_PROP_H void zprop_register_number(int, const char *, uint64_t,
-    zprop_attr_t, int, const char *, const char *);
+    zprop_attr_t, int, const char *, const char *,
+    const struct zfs_mod_supported_features *);
 _ZFS_PROP_H void zprop_register_index(int, const char *, uint64_t, zprop_attr_t,
-    int, const char *, const char *, const zprop_index_t *);
+    int, const char *, const char *, const zprop_index_t *,
+    const struct zfs_mod_supported_features *);
 _ZFS_PROP_H void zprop_register_hidden(int, const char *, zprop_type_t,
-    zprop_attr_t, int, const char *);
+    zprop_attr_t, int, const char *, const struct zfs_mod_supported_features *);
 
 /*
  * Common routines for zfs and zpool property management