Epoll on regular files

问题:

Can epoll (on Linux) be somehow useful for regular files? I know it's primarily used with sockets but just wonder.

回答1:

Not really. epoll only makes sense for file descriptors which would normally exhibit blocking behavior on read/write, like pipes and sockets. Normal file descriptors will always either return a result or end-of-file more or less immediately, so epoll wouldn't do anything useful for them.

回答2:

I think, it will fail at epoll_ctl with EPERM:

   EPERM  The target file fd does not support epoll. 

if the file has no poll() interface.

The actual code is http://lxr.linux.no/#linux+v3.1/fs/eventpoll.c#L1373

1373    /* The target file descriptor must support poll */ 1374        error = -EPERM; 1375        if (!tfile->f_op || !tfile->f_op->poll) 1376                goto error_tgt_fput; 1377 

文章来源: Epoll on regular files