int __pmProcessPipe(__pmExecCtl_t **handle, const char *type, int toss, FILE **fp);
int __pmProcessPipeClose(FILE *fp);
cc ... -lpcp
This documentation is intended for internal Performance Co-Pilot (PCP) developer use.
These interfaces are not part of the PCP APIs that are guaranteed to remain fixed across releases, and they may not work, or may provide different semantics at some point in the future.
Within the libraries and applications of the Performance Co-Pilot (PCP) these routines are provide a convenient and safe alternative to popen(3) and pclose(3) for executing commands in a separate process that is connected to the caller by a pipe.
Setting up the command and arguments is fully documented in __pmProcessAddArg(3) and is identical to the procedure used to setup __pmProcessExec(3).
Once all the command name and arguments have been registered calling __pmProcessPipe uses a pipe (2), fork (2) and execvp (2) sequence to execute the command.
The type argument needs to be “r” to read from the pipe, else “w” to write to the pipe.
The argument toss may be used to assign some or all of the standard I/O streams for the command to /dev/null - specifically toss is either PM_EXEC_TOSS_NONE to keep all I/O streams the same as the parent process, else the bit-wise or of PM_EXEC_TOSS_STDIN and/or PM_EXEC_TOSS_STDOUT and/or PM_EXEC_TOSS_STDERR to reassign stdin, stdout and stderr respectively. PM_EXEC_TOSS_ALL is a convenience macro equivalent to PM_EXEC_TOSS_STDIN | PM_EXEC_TOSS_STDOUT | PM_EXEC_TOSS_STDERR.
Obviously some combinations of argument values make no sense, e.g. type equal to “r” and PM_EXEC_TOSS_STDOUT set in toss or type equal to “w” and PM_EXEC_TOSS_STDIN set in type.
__pmProcessPipe returns a standard I/O stream for the pipe via the fp argument.
Once the caller determines all the work has been done, __pmProcessPipeClose should be called.
Nested calling of __pmProcessExec(3) and/or __pmProcessPipe is not allowed. Once __pmProcessAddArg(3) is called with handle set to NULL to start the registration and execution sequence any attempt to start a second registration sequence will be blocked until the first one is completed by calling __pmProcessExec(3) or __pmProcessPipe.
execvp(2), fork(2), pclose(2), pipe(2), popen(2), __pmProcessAddArg(3), __pmProcessExec(3) and waitpid(3).
If successful __pmProcessPipe returns 0. Other conditions are rare (e.g. alloc failure) and are indicated by a return value that can be decoded using pmErrStr(3).
The return status from __pmProcessPipeClose is a little more complicated. If the command completes with an exit status of 0, the return value is 0. Return values less than 0 indicate a more serious error and the value can be decoded using pmErrStr(3). If the command was executed, but did not exit with status of 0 then the return value is an encoding of the waitpid(2) status as follows: 2000 if something unknown went wrong, else if 1000 + signal number of the command was killed or stopped by a signal, else the exit status of the command.
The man page __pmProcessPipeClose(3) is an alias of __pmProcessPipe(3).