zkSysTypes.h is a portable wrapper for the POSIX header <sys/types.h>. It is part of the libzk library because <sys/types.h> doesn't exist in Standard C.

zkSysTypes.h - Supported Types from <sys/types.h>
Type Description
blkcnt_t Used for file block counts.
blksize_t Used for block sizes.
dev_t Arithmetic type used for device numbers.
gid_t Arithmetic type used for group IDs.
ino_t Arithmetic type used for file serial numbers.
mode_t Arithmetic type used for file attributes.
nlink_t Arithmetic type used for link counts.
off_t Signed Arithmetic type used for file sizes.
pid_t Signed Arithmetic type used for process and process group IDs.
ssize_t Arithmetic type used for a count of bytes or an error indication.
suseconds_t A signed arithmetic type used for time in microseconds.
uid_t Arithmetic type used for user IDs.
useconds_t Integral type used for time in microseconds.