inotify 报告变化，但不是完整历史记录

from pathlib import Path
from tempfile import TemporaryDirectory
import ctypes,os,struct

MODIFY=0x2;ATTRIB=0x4;CLOSE_WRITE=0x8;MOVED_FROM=0x40;MOVED_TO=0x80
CREATE=0x100;DELETE=0x200;DELETE_SELF=0x400;MOVE_SELF=0x800;OVERFLOW=0x4000;IGNORED=0x8000
libc=ctypes.CDLL(None,use_errno=True)
libc.inotify_init1.argtypes=[ctypes.c_int];libc.inotify_init1.restype=ctypes.c_int
libc.inotify_add_watch.argtypes=[ctypes.c_int,ctypes.c_char_p,ctypes.c_uint32];libc.inotify_add_watch.restype=ctypes.c_int
header=struct.Struct('iIII')
with TemporaryDirectory(prefix='xbcatm-inotify-') as directory:
    root=Path(directory);fd=libc.inotify_init1(os.O_NONBLOCK|os.O_CLOEXEC);assert fd>=0,os.strerror(ctypes.get_errno())
    def watch(path,mask):
        wd=libc.inotify_add_watch(fd,os.fsencode(path),mask);assert wd>=0,os.strerror(ctypes.get_errno());return wd
    def drain():
        events=[]
        while True:
            try:data=os.read(fd,65536)
            except BlockingIOError:return events
            offset=0
            while offset<len(data):
                wd,mask,cookie,length=header.unpack_from(data,offset);offset+=header.size
                name=data[offset:offset+length].split(b'\0',1)[0].decode();offset+=length
                events.append((wd,mask,cookie,name))
    try:
        parent=watch(root,MODIFY|CLOSE_WRITE|CREATE|DELETE|MOVED_FROM|MOVED_TO)
        sub=root/'sub';sub.mkdir();drain();(sub/'unwatched').touch();assert drain()==[]
        nested=watch(sub,CREATE);(sub/'watched').touch();assert any(wd==nested and mask&CREATE and name=='watched' for wd,mask,_,name in drain())
        print('a directory watch is not recursive; adding a child-directory watch observes its new entries')
        counter=root/'counter';stream=os.open(counter,os.O_CREAT|os.O_WRONLY,0o600);drain()
        try:
            for _ in range(3):os.write(stream,b'x')
        finally:os.close(stream)
        events=drain();assert sum(wd==parent and bool(mask&MODIFY) and name=='counter' for wd,mask,_,name in events)==1
        moved=root/'moved';counter.rename(moved);events=drain()
        before=next(e for e in events if e[1]&MOVED_FROM and e[3]=='counter');after=next(e for e in events if e[1]&MOVED_TO and e[3]=='moved')
        assert before[2]==after[2]!=0
        print('three unread identical modifications coalesce; rename FROM/TO events share a nonzero cookie')
        target=root/'target';target.write_bytes(b'old');file_watch=watch(target,MODIFY|ATTRIB|DELETE_SELF|MOVE_SELF);drain()
        replacement=root/'replacement';replacement.write_bytes(b'new');drain();replacement.replace(target);events=drain()
        assert any(wd==file_watch and mask&IGNORED for wd,mask,_,_ in events)
        assert any(wd==parent and mask&MOVED_TO and name=='target' for wd,mask,_,name in events)
        assert not any(wd==parent and mask&CLOSE_WRITE and name=='target' for wd,mask,_,name in events)
        target.write_bytes(b'newer');events=drain()
        assert any(wd==parent and mask&MODIFY and name=='target' for wd,mask,_,name in events)
        assert all(wd!=file_watch for wd,_,_,_ in events)
        print('replacement invalidates the old file watch; the parent-directory watch continues to observe the pathname')
        burst=root/'burst';burst.mkdir();drain();watch(burst,CREATE)
        limit=int(Path('/proc/sys/fs/inotify/max_queued_events').read_text());assert 0<limit<=32768,'use a disposable environment with a bounded queue limit'
        for number in range(limit+8):(burst/str(number)).touch()
        events=drain();assert any(wd==-1 and mask&OVERFLOW for wd,mask,_,_ in events)
        current=len(list(burst.iterdir()));assert current==limit+8
        print('actual queue overflow:',len(events),'events retained for',current,'creates; rescan sees the current entries')
    finally:os.close(fd)