10-12-2005
Pipes and fifos cannot overflow. A fifo, aka named pipe, is more of a interprocess communication mechanism than a file. Unlimited writes to fifos are required by Posix. If you exceed PIPE_BUF, you lose the guarantee of atomicity. This only has an effect in the case of multiple writing processes. Some people wanted a PIPE_MAX and such a constant is available but it is the same as the max value in a ssize_t field. Setting O_NONBLOCK and writing more than PIPE_BUF will result in partial writes and a poorly designed application could lose data under those circumstances, but that is not exactly an overflow.
With one process reading from a pipe and another writing to a pipe, they will take turns running. In theory, a pipeline like:
yes | cat > /dev/null
can run for all eternity and that continues to be true if a fifo is used instead.
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PIPE(2) System Calls Manual PIPE(2)
NAME
pipe - create an interprocess communication channel
SYNOPSIS
pipe(fildes)
int fildes[2];
DESCRIPTION
The pipe system call creates an I/O mechanism called a pipe. The file descriptors returned can be used in read and write operations. When
the pipe is written using the descriptor fildes[1] up to 4096 bytes of data are buffered before the writing process is suspended. A read
using the descriptor fildes[0] will pick up the data.
It is assumed that after the pipe has been set up, two (or more) cooperating processes (created by subsequent fork calls) will pass data
through the pipe with read and write calls.
The shell has a syntax to set up a linear array of processes connected by pipes.
Read calls on an empty pipe (no buffered data) with only one end (all write file descriptors closed) returns an end-of-file.
Pipes are really a special case of the socketpair(2) call and, in fact, are implemented as such in the system.
A signal is generated if a write on a pipe with only one end is attempted.
RETURN VALUE
The function value zero is returned if the pipe was created; -1 if an error occurred.
ERRORS
The pipe call will fail if:
[EMFILE] Too many descriptors are active.
[ENFILE] The system file table is full.
[EFAULT] The fildes buffer is in an invalid area of the process's address space.
SEE ALSO
sh(1), read(2), write(2), fork(2), socketpair(2)
BUGS
Should more than 4096 bytes be necessary in any pipe among a loop of processes, deadlock will occur.
4th Berkeley Distribution August 26, 1985 PIPE(2)