gistfile1.txt

Traditionally, System V has returned the error EAGAIN
for a nonblocking I/O operation that cannot be satisfied,
while Berkeley-derived implementations have returned the
error EWOULDBLOCK. Because of this history, the POSIX
specification says either may be returned for this case.
Fortunately, most current systems define these two error
codes to be the same (check your system's <sys/errno.h>
header), so it doesn't matter which one we use. In this
text, we use EWOULDBLOCK.