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NAME

       explain_wait4 - explain wait4(2) errors

SYNOPSIS

       #include <libexplain/wait4.h>
       const  char  *explain_wait4(int  pid,  int *status, int options, struct
       rusage *rusage);
       const char *explain_errno_wait4(int errnum, int pid, int  *status,  int
       options, struct rusage *rusage);
       void  explain_message_wait4(char  *message,  int message_size, int pid,
       int *status, int options, struct rusage *rusage);
       void explain_message_errno_wait4(char *message, int  message_size,  int
       errnum, int pid, int *status, int options, struct rusage *rusage);

DESCRIPTION

       These  functions may be used to obtain explanations for errors returned
       by the wait4(2) system call.

   explain_wait4
       const char *explain_wait4(int pid, int  *status,  int  options,  struct
       rusage *rusage);

       The explain_wait4 function is used to obtain an explanation of an error
       returned by the wait4(2) system  call.   The  least  the  message  will
       contain  is  the  value of strerror(errno), but usually it will do much
       better, and indicate the underlying cause in more detail.

       The errno global variable will be used to obtain the error value to  be
       decoded.

       This  function  is  intended  to  be  used  in a fashion similar to the
       following example:
              if (wait4(pid, status, options, rusage) < 0)
              {
                  fprintf(stderr, "%s\n", explain_wait4(pid, status, options, rusage));
                  exit(EXIT_FAILURE);
              }

       pid     The original pid, exactly as  passed  to  the  wait4(2)  system
               call.

       status  The  original  status, exactly as passed to the wait4(2) system
               call.

       options The original options, exactly as passed to the wait4(2)  system
               call.

       rusage  The  original  rusage, exactly as passed to the wait4(2) system
               call.

       Returns:
               The message explaining  the  error.   This  message  buffer  is
               shared by all libexplain functions which do not supply a buffer
               in their argument list.  This will be overwritten by  the  next
               call  to  any  libexplain  function  which  shares this buffer,
               including other threads.

       Note: This function is not thread safe,  because  it  shares  a  return
       buffer across all threads, and many other functions in this library.

   explain_errno_wait4
       const  char  *explain_errno_wait4(int errnum, int pid, int *status, int
       options, struct rusage *rusage);

       The explain_errno_wait4 function is used to obtain an explanation of an
       error returned by the wait4(2) system call.  The least the message will
       contain is the value of strerror(errnum), but usually it will  do  much
       better, and indicate the underlying cause in more detail.

       This  function  is  intended  to  be  used  in a fashion similar to the
       following example:
              if (wait4(pid, status, options, rusage) < 0)
              {
                  int err = errno;
                  fprintf(stderr, "%s\n", explain_errno_wait4(err,
                      pid, status, options, rusage));
                  exit(EXIT_FAILURE);
              }

       errnum  The error value to be decoded, usually obtained from the  errno
               global  variable  just before this function is called.  This is
               necessary if you need to call any code between the system  call
               to  be explained and this function, because many libc functions
               will alter the value of errno.

       pid     The original pid, exactly as  passed  to  the  wait4(2)  system
               call.

       status  The  original  status, exactly as passed to the wait4(2) system
               call.

       options The original options, exactly as passed to the wait4(2)  system
               call.

       rusage  The  original  rusage, exactly as passed to the wait4(2) system
               call.

       Returns:
               The message explaining  the  error.   This  message  buffer  is
               shared by all libexplain functions which do not supply a buffer
               in their argument list.  This will be overwritten by  the  next
               call  to  any  libexplain  function  which  shares this buffer,
               including other threads.

       Note: This function is not thread safe,  because  it  shares  a  return
       buffer across all threads, and many other functions in this library.

   explain_message_wait4
       void  explain_message_wait4(char  *message,  int message_size, int pid,
       int *status, int options, struct rusage *rusage);

       The  explain_message_wait4  function  may  be  used   to    obtain   an
       explanation  of  an  error  returned  by the wait4(2) system call.  The
       least the message will contain is the  value  of  strerror(errno),  but
       usually  it  will  do much better, and indicate the underlying cause in
       more detail.

       The errno global variable will be used to obtain the error value to  be
       decoded.

       This  function  is  intended  to  be  used  in a fashion similar to the
       following example:
              if (wait4(pid, status, options, rusage) < 0)
              {
                  char message[3000];
                  explain_message_wait4(message, sizeof(message),
                      pid, status, options, rusage);
                  fprintf(stderr, "%s\n", message);
                  exit(EXIT_FAILURE);
              }

       message The location in which to store  the  returned  message.   If  a
               suitable  message  return  buffer is supplied, this function is
               thread safe.

       message_size
               The size in bytes  of  the  location  in  which  to  store  the
               returned message.

       pid     The  original  pid,  exactly  as  passed to the wait4(2) system
               call.

       status  The original status, exactly as passed to the  wait4(2)  system
               call.

       options The  original options, exactly as passed to the wait4(2) system
               call.

       rusage  The original rusage, exactly as passed to the  wait4(2)  system
               call.

   explain_message_errno_wait4
       void  explain_message_errno_wait4(char  *message, int message_size, int
       errnum, int pid, int *status, int options, struct rusage *rusage);

       The explain_message_errno_wait4 function  may  be  used  to  obtain  an
       explanation  of  an  error  returned  by the wait4(2) system call.  The
       least the message will contain is the value  of  strerror(errnum),  but
       usually  it  will  do much better, and indicate the underlying cause in
       more detail.

       This function is intended to be  used  in  a  fashion  similar  to  the
       following example:
              if (wait4(pid, status, options, rusage) < 0)
              {
                  int err = errno;
                  char message[3000];
                  explain_message_errno_wait4(message, sizeof(message), err,
                      pid, status, options, rusage);
                  fprintf(stderr, "%s\n", message);
                  exit(EXIT_FAILURE);
              }

       message The  location  in  which  to  store the returned message.  If a
               suitable message return buffer is supplied,  this  function  is
               thread safe.

       message_size
               The  size  in  bytes  of  the  location  in  which to store the
               returned message.

       errnum  The error value to be decoded, usually obtained from the  errno
               global  variable  just before this function is called.  This is
               necessary if you need to call any code between the system  call
               to  be explained and this function, because many libc functions
               will alter the value of errno.

       pid     The original pid, exactly as  passed  to  the  wait4(2)  system
               call.

       status  The  original  status, exactly as passed to the wait4(2) system
               call.

       options The original options, exactly as passed to the wait4(2)  system
               call.

       rusage  The  original  rusage, exactly as passed to the wait4(2) system
               call.

SEE ALSO

       wait4(2)
               wait for process to change state

       explain_wait4_or_die(3)
               wait for process to change state and report errors

COPYRIGHT

       libexplain version 0.19
       Copyright (C) 2008 Peter Miller

                                                              explain_wait4(3)