setcompat(2)                                         setcompat(2)



NAME
     setcompat, getcompat - set or get process compatibility mode

SYNOPSIS
     #include <compat.h>

     int setcompat(flags)
     int flags;

     int getcompat();

DESCRIPTION
     setcompat sets a process's compatibility mode according to
     the flags argument.  The argument governs the type of
     compatibility enforced.  flags may be COMPAT_SVID for
     strictest adherence to the System V interface definition,
     COMPAT_POSIX to enable all POSIX functionality, or the
     bitwise OR of one or more of the following symbolic
     constants.  If set, other flags always take precedence over
     COMPAT_SVID.

     COMPAT_BSDNBIO
          Changes the error handling in 4.2 BSD nonblocking I/O
          code.  read and write system calls on slow devices,
          that is, terminals, which are marked for non-blocking
          may return -1 with errno set to EWOULDBLOCK instead of
          returning 0.  (Operations which may block, that is,
          connect, accept, and recv on sockets which are marked
          for nonblocking always return an error and set errno to
          EWOULDBLOCK.)

     COMPAT_BSDGROUPS
          Enables the use of the 4.2 BSD groups code which
          permits users to be members of more than one group
          simultaneously and creates files whose group is
          determined by the group of the directory in which the
          file is created.

     COMPAT_BSDSETUGID
          When selected, changes the behavior of the setuid and
          setgid calls to be BSD-compatible; that is, no handling
          of the saved set-user (group) ID from exec.  When
          cleared, the setreuid and setregid calls behave as
          setuid and setgid, respectively.

     COMPAT_BSDSIGNALS
          Allows a process to use 4.2 BSD-compatible signals.
          The state of this flag may not be changed unless no
          signals are pending, caught, or held.  This option
          enables reliable signal delivery.  Caught signals will
          be held while a signal handler is invoked and reset
          upon exit from the signal hander.



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setcompat(2)                                         setcompat(2)



     COMPAT_BSDTTY
          Enables 4.2 BSD job control.  When first set, this
          process and its descendants will be identified as 4.2
          processes via a bit in the flag word of the kernel proc
          data structure.  Membership in a 4.2 process group
          persists across exec system calls.  Jobs that are 4.2
          process group members are effected by job control
          signals.  When COMPAT_BSDTTY is set the setpgrp system
          call may be used to manipulate the process group of
          other processes.  This flag may only be used in
          conjunction with the COMPAT_BSDSIGNALS flag.  Normally,
          COMPAT_BSDTTY is set by a login shell.

     COMPAT_CLRPGROUP
          Disables 4.2 BSD job control.  Resets the 4.2 process
          group bit in the flag word of the kernel proc data
          structure.  It may be used by a V.2 process which wants
          to sever any job control associations with an invoking
          shell (for itself and its descendants).  This bit
          provides a ``one shot'' clear.  When read by getcompat,
          this bit is always zero.

     COMPAT_EXEC
          If this flag is set, compatibility flags are inherited
          across exec system calls.  To provide child process
          with a System V interface environment, both the
          COMPAT_SVID and the COMPAT_EXEC flags must be set by
          ORing the flags.

     COMPAT_SYSCALLS
          If selected, read, write, ioctl, or wait calls which
          are interrupted by a signal handler will not return an
          EINTR error, but will instead resume at the point they
          were interrupted.  This flag may only be used in
          conjunction with the COMPAT_BSDSIGNALS flag.

     COMPAT_BSDCHOWN
          If selected, chown(2) is restricted to processes with
          superuser privileges.  However, a process with
          effective user ID equal to the user ID of the file, but
          without superuser privileges, can change the group ID
          of the file to the effective group ID of the process or
          to one of the process's supplementary group IDs.

     COMPAT_BSDNOTRUNC
          If selected, pathname components longer than NAME_MAX
          generate an error.

     getcompat returns the current process compatibility flags.
     By default, compatibility flags are preserved across fork
     calls and are reset by exec calls (see COMPAT_EXEC earlier
     in this section).



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setcompat(2)                                         setcompat(2)



     The default process compatibility flags are COMPAT_BSDPROT
     and COMPAT_BSDNBIO.

STATUS MESSAGES AND VALUES
     Upon successful completion, setcompat returns the previous
     compatibility mask and getcompat returns the current
     compatibility mask.  Otherwise, a value of -1 is returned
     and errno is set to indicate the error.

     The setcompat command will return the following error code.

     EINVAL
          flag results in a change in the state of the
          COMPAT_BSDSIGNALS bit and a signal is currently
          pending, caught, or held.

     EINVAL
          flag is either COMPAT_BSDTTY or COMPAT_SYSCALLS and the
          COMPAT_BSDSIGNALS are also not set.

SEE ALSO
     exec(2), fork(2), sigvec(2), set42sig(3), signal(3),
     setuid(3), termio(7)
































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