diff options
| -rw-r--r-- | man7/pipe.7 | 41 |
1 files changed, 27 insertions, 14 deletions
diff --git a/man7/pipe.7 b/man7/pipe.7 index c10cd29b3a..d9983f795a 100644 --- a/man7/pipe.7 +++ b/man7/pipe.7 @@ -30,7 +30,7 @@ A pipe has a and a .IR "write end" . Data written to the write end of a pipe can be read -by a process that has the read end of the pipe open. +from the read end of the pipe. A pipe is created using .BR pipe (2), @@ -58,23 +58,14 @@ See for further details. .IR Note : although FIFOs have a pathname in the file system, -I/O on FIFOs does not involve disk operations. +I/O on FIFOs does not involve operations on the underlying device +(if there is one). .SS "I/O on Pipes and FIFOs" The only difference between pipes and FIFOs is the manner in which they are created and opened. Once these tasks have been accomplished, I/O on pipes and FIFOs has exactly the same semantics. -I/O is performed using -.BR read (2) -and -.BR write (2). - -The communication channel provided by a pipe is a -.IR "byte stream" : -there is no concept of message boundaries; -data can be read and written in arbitrary amounts. -By default, I/O on pipes and FIFOs is blocking. If a process attempts to read from an empty pipe, then .BR read (2) will block until data is available. @@ -89,6 +80,10 @@ operation to enable the .B O_NONBLOCK open file status flag. +The communication channel provided by a pipe is a +.IR "byte stream" : +there is no concept of message boundaries. + If all file descriptors referring to the write end of a pipe have been closed, then an attempt to .BR read (2) @@ -116,9 +111,9 @@ this ensures that end-of-file and .BR SIGPIPE / EPIPE are delivered when appropriate. -It is not possible to use +It is not possible to apply .BR lseek (2) -to randomly access the bytes in a pipe. +to a pipe. .SS "Pipe Capacity" A pipe has a limited capacity. If the pipe is full, then a @@ -206,6 +201,24 @@ the caller should check the return value from .BR write (2) to see how many bytes were actually written), and these bytes may be interleaved with writes by other processes. +.SS "Open File Status Flags" +The only open file status flags that can be meaningfully applied to +a pipe or FIFO are +.B O_NONBLOCK +and +.BR O_ASYNC . + +Setting the +.B O_ASYNC +flag for the read end of a pipe causes a signal +.RB ( SIGIO +by default) to be generated when new input becomes available on the pipe +(see +.BR fcntl (2) +for details). +On Linux, +.B O_ASYNC +is supported for pipes and FIFOs only since kernel 2.6. .SS "Portability notes" On some systems (but not Linux), pipes are bidirectional: data can be transmitted in both directions between the pipe ends. |