x/sys/unix: add cachestat system call

The cachestat system call is an alternative to mincore that
offers more extensive page cache statistics, aiming to enhance
scalability. It was added on Linux 6.5.

Fixes golang/go#61917

Author: mauri870

unix/linux/types.go

@@ -461,6 +461,20 @@ struct my_can_bittiming_const {
 
 struct riscv_hwprobe {};
 #endif
+
+// copied from /usr/include/uapi/linux/mman.h
+struct cachestat_range {
+	__u64 off;
+	__u64 len;
+};
+
+struct cachestat {
+	__u64 nr_cache;
+	__u64 nr_dirty;
+	__u64 nr_writeback;
+	__u64 nr_evicted;
+	__u64 nr_recently_evicted;
+};
 */
 import "C"
 
@@ -5813,3 +5827,6 @@ const (
 type SchedAttr C.struct_sched_attr
 
 const SizeofSchedAttr = C.sizeof_struct_sched_attr
+
+type Cachestat C.struct_cachestat
+type CachestatRange C.struct_cachestat_range

unix/syscall_linux.go

@@ -2482,3 +2482,5 @@ func SchedGetAttr(pid int, flags uint) (*SchedAttr, error) {
 	}
 	return attr, nil
 }
+
+//sys	Cachestat(fd uint, crange *CachestatRange, cstat *Cachestat, flags uint) (err error)