illumos gate

Today the only way to get the createtxg for a bookmark from user land is to use:

int
lzc_get_bookmarks(const char *fsname, nvlist_t *props, nvlist_t **bmarks) {
return (lzc_ioctl(ZFS_IOC_GET_BOOKMARKS, fsname, props, bmarks));
}

This interface lists of the bookmarks for a given filesystem and fetches the requested set of properties.

If we already have the bookmark in question, we just want to fetch the createtxg property for it. Rather than having to list all bookmarks and filter we'd like to have an API that takes a bookmark and returns the property.