io_waitread man page
io_waitread — read from a descriptor
int io_waitread(int64 fd,char* buf,int64 len);
io_waitread tries to read len bytes of data from descriptor fd into buf, buf, ..., buf[len-1]. (The effects are undefined if len is 0 or smaller.) There are several possible results:
- o_waitread returns an integer between 1 and len: This number of bytes was available for immediate reading; the bytes were read into the beginning of buf. Note that this number can be, and often is, smaller than len; you must not assume that io_waitread always succeeds in reading exactly len bytes.
- io_waitread returns 0: No bytes were read, because the descriptor is at end of file. For example, this descriptor has reached the end of a disk file, or is reading an empty pipe that has been closed by all writers.
- io_waitread returns -3, setting errno to something other than EAGAIN: No bytes were read, because the read attempt encountered a persistent error, such as a serious disk failure (EIO), an unreachable network (ENETUNREACH), or an invalid descriptor number (EBADF).
io_nonblock(3), io_waitread(3), io_waitreadtimeout(3)
io_tryread(3), io_tryreadtimeout(3), io_trywrite(3).