io_pipe creates a new UNIX pipe. The pipe can receive data and provide
data; any bytes written to the pipe can then be read from the pipe in the same
A pipe is typically stored in an 8192-byte memory buffer; the exact number
depends on the UNIX kernel. Bytes are written to the end of the buffer and read
from the beginning of the buffer. Once a byte has been read, it is eliminated
from the buffer, making space for another byte to be written; readers cannot
rewind a pipe to read old data. Once 8192 bytes have been written to the
buffer, the pipe will not be ready for further writing until some of the bytes
have been read. Once all the bytes written have been read, the pipe will not be
ready for further reading until more bytes are written.
io_pipe sets d to the number of a new descriptor reading from the pipe, and
sets d to the number of a new descriptor writing to the pipe. It then
returns 1 to indicate success. If something goes wrong, io_pipe returns 0,
setting errno to indicate the error; in this case it frees any memory that it
allocated for the new pipe, and it leaves d alone.