NAME

       __pmProcessAddArg, __pmProcessUnpickArgs, __pmProcessExec - process execution support

C SYNOPSIS

       #include "pmapi.h"
       #include "libpcp.h"

       int __pmProcessAddArg(__pmExecCtl_t **handle, const char *arg);
       int __pmProcessUnpickArgs(__pmExecCtl_t **handle, const char *command);
       int __pmProcessExec(__pmExecCtl_t **handle, int toss, int wait);

       cc ... -lpcp

CAVEAT

       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.

DESCRIPTION

       Within the libraries and applications of the Performance Co-Pilot (PCP)  these  routines  are  provide  a
       convenient and safe alternative to system(3) for executing commands in a separate process.

       Use __pmProcessAddArg to register the executable and command arguments in order.  handle should be set to
       NULL before the first call to __pmProcessAddArg for a particular command execution and it will be set  to
       an  opaque  pointer to data structures that are manipulated in __pmProcessAddArg, __pmProcessExec and the
       related __pmProcessPipe(3) routines.

       When called with handle set to NULL arg is treated as  the  name  of  the  command  to  be  executed  and
       subsequent  calls  (if any) are for the arguments to that command.  The name of the command can be a full
       pathname, or the name of an executable that can be found on  the  current  $PATH  as  per  the  rules  of
       execvp(2) that is used by __pmProcessExec.

       __pmProcessUnpickArgs is a convenience wrapper to assist conversion of code that assumes the command is a
       shell command that has been prepared for use with system(3) or popen(3) in existing code.  The  arguments
       in  command  are picked off one-by-one and used to call __pmProcessAddArgs.  The parser is simple, as the
       routine is designed for simple shell command syntax, where arguments are separated by one or more  spaces
       but  embedded  spaces  within  an  argument  are allowed if the arguement is enclosed in single or double
       quotes.  More advanced  shell  syntax  like  escape  characters  and  input-output  redirection  are  not
       recognized.

       Once  all  the command name and arguments have been registered calling __pmProcessExec uses a fork(2) and
       execvp(2) sequence to execute the command.

       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.

       The wait argument should be PM_EXEC_WAIT if __pmProcessExec should wait for completion of the command and
       harvest  the  exit  status,  else  PM_EXEC_NOWAIT  in  which  case  __pmProcessExec  returns  immediately
       (effectively running the command in the background).

       Nested calling of __pmProcessExec and/or __pmProcessPipe(3) is not allowed.   Once  __pmProcessAddArg  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
       or __pmProcessPipe(3).

DIAGNOSTICS

       If  successful  __pmProcessAddArg  returns 0.  Other conditions are rare (e.g. memory allocation failure)
       and are indicated by a return value that can be decoded using pmErrStr(3).   When  an  error  does  occur
       __pmProcessAddArg  cleans  up  any  allocations  made in the current call and uses handle to clean up any
       allocations made by previous calls so there is no need for the caller to worry about  memory  leaks,  and
       then (re)sets handle to NULL before returning.

       __pmProcessUnpickArgs  returns  0  on  success.   In  the  case  of  an unterminated string, a message is
       generated and PM_ERR_GENERIC is returned.  Other return values less than 0 indicate a more serious  error
       and  the  value  can  be  decoded using pmErrStr(3).  When an error does occur the clean up is similar to
       __pmProcessAddArg so there is no need for the caller to worry about memory leaks.

       The return status from __pmProcessExec is more complicated.  If either PM_EXEC_NOWAIT  is  specified,  or
       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.

SEE ALSO

       execvp(2), fork(2), __pmProcessPipe(3), popen(3), system(3) and waitpid(3).