Problem handling file I/O with libevent2

Question

I worked with libevent2 for some time, but usually I used it to handle network I/O (using sockets). Now I need to read many different files so I also wanted to use it. I created this code:

int file = open(filename, O_RDONLY);
struct event *ev_file_read = event_new(ev_base, file, EV_READ | EV_PERSIST, read_file, NULL);

if(event_add(ev_file_read, NULL))
        error("adding file event");

Unfortunately it doesn't work. I get this message when trying to add event:

[warn] Epoll ADD(1) on fd 7 failed. Old events were 0; read change was 1 (add); write change was 0 (none): Operation not permitted adding file event: Operation not permitted

The file exists and has rights to read/write.

Anyone has any idea how to handle file IO using libevent? I thought also about bufferred events, but in API there's only function bufferevent_socket_new() which doesn't apply here.

Thanks in advance.

Answer 1

I needed libevent to read many files regarding priorities. The problem was in epoll not in libevent. Epoll doesn't support regular Unix files.

To solve it I forced libevent not to use epoll:

    struct event_config *cfg = event_config_new();

event_config_avoid_method(cfg, "epoll");

ev_base = event_base_new_with_config(cfg);  
    event_config_free(cfg);

Next method on the preference list was poll, which fully support files just as I wanted to.

Thank you all for answers.

Answer 2

Makes no sense to register regular file descriptors with libevent. File descriptors associated with regular files shall always select true for ready to read, ready to write, and error conditions.