Function writeback_fds

src/poll.rs:202–260

(
    ctx: &mut VmCtx,
    out_ptr: u32,
    pollfds: &Vec<libc::pollfd>,
    fd_data: &Vec<(u64, SubscriptionFdType)>,
)

#[external_calls(from_posix, from_poll_revents, Some)]
#[external_methods(to_event_type)]
pub fn writeback_fds(
    ctx: &mut VmCtx,
    out_ptr: u32,
    pollfds: &Vec<libc::pollfd>,
    fd_data: &Vec<(u64, SubscriptionFdType)>,
) -> RuntimeResult<u32> {
    let mut num_events_written = 0;
    let mut event_idx = 0;
    while event_idx < fd_data.len() {
        body_invariant!(ctx_safe(ctx));
        body_invariant!(trace_safe(trace, ctx));

        let (userdata, sub_type) = fd_data[event_idx];
        // let typ = match sub_type {
        //     SubscriptionFdType::Read => EventType::FdRead,
        //     SubscriptionFdType::Write => EventType::FdWrite,
        // };
        let typ = sub_type.to_event_type();

        let pollfd = pollfds[event_idx];

        // if no event ocurred, continue
        if pollfd.revents == 0 {
            continue;
        }

        let event_offset = (num_events_written * Event::WASI_SIZE) as usize;
        if !ctx.fits_in_lin_mem_usize(out_ptr as usize + event_offset, Event::WASI_SIZE as usize) {
            return Err(Eoverflow);
        }

        // get the number of bytes for reading...
        // TODO: If we want, we can remove this, and always return 1 for reads
        let nbytes = match typ {
            EventType::FdRead => trace_fionread(ctx, HostFd::from_raw(pollfd.fd as usize))? as u64,
            // no way to check number of bytes for writing
            _ => 0,
        };

        let fd_readwrite = EventFdReadWrite {
            nbytes,
            flags: EventRwFlags::from_posix(pollfd.revents),
        };

        let error = RuntimeError::from_poll_revents(pollfd.revents);

        let event = Event {
            userdata,
            error,
            typ,
            fd_readwrite: Some(fd_readwrite),
        };
        event.write(ctx, out_ptr + event_offset as u32);
        num_events_written += 1;

        event_idx += 1;
    }
    return Ok(num_events_written);