MPROTECT(2)                          SysV                          MPROTECT(2)



NAME
     mprotect - assign protection to region mapped in virtual memory

SYNOPSIS
     #include <sys/mman.h>

     mprotect(addr, len, prot)
     caddr_t addr;
     int len, prot;

DESCRIPTION
     mprotect modifies the access protection of a mapped file or shared memory
     region. addr and len arguments specify the address and length of the
     region to be modified.  This region must reside within a mapping
     established via an earlier call to MMAP.  The specified region is
     expanded to cover an integral number of system segments.  That is, the
     segment containing addr, the segment containing addr+len-1 and any
     intervening segments are processed.  The segment size is as follows: 32K
     for Apollo M68K (M68010, M68020, M68030) workstations, 512K for Apollo
     M88K (AT) workstations, and 256K for Apollo M68K (M68040) workstations.

     <sys/mman.h> defines the possible settings for prot:

     /* protections are chosen from these bits, ORed together */

     #define  PROT_READ        0x04    /* mapped region can be read */
     #define  PROT_WRITE       0x02    /* mapped region can be written */
     #define  PROT_EXEC        0x01    /* mapped region can be executed */
     #define  PROT_NONE        0x00    /* mapped region cannot be accessed */

     The prot argument can be PROT_NONE, or any combination of PROT_READ,
     PROT_WRITE, and PROT_EXEC ORed together.  If PROT_NONE is not specified,
     access permissions may be granted to the region in addition to those
     explicitly requested, except that write access will not be granted unless
     PROT_WRITE is specified.

     If the region is a mapped file which was mapped with MAP_SHARED, the
     mprotect function grants read or execute access permission only if the
     file descriptor used to map the file is open for reading and grants write
     access permission only if the file descriptor used to map the file is
     open for writing.

     If the region is a mapped file which was mapped with MAP_PRIVATE, the
     behavior is dependent on the environment.  In an AES environment, the
     mprotect function grants read, write, or execute access permission only
     if the file descriptor used to map the file is open for reading.  In a
     non-AES environment, the behavior is identical to that in the MAP_SHARED
     case.

     If the region is a shared memory region which was mapped with
     MAP_ANONYMOUS, mprotect grants all requested access permissions.

NOTES
     In Domain/OS, the unit of mapping and protection is the segment.

SEE ALSO
     madvise(2), mmap(2), mset(2).

DIAGNOSTICS
     A successful call returns 0.  An unsuccessful call returns -1 and sets
     errno as indicated below.

ERRORS
     mprotect will fail if any of the following is true:

     [EINVAL]   An invalid protection mode was specified.

     [ENOENT]   No region is mapped at the specified address.

     [EACCESS]  Attempt to change the protection to a mode precluded by file
                access proctections.

     [ETXTBSY]  The file is a pure-procedure (shared text) file that is being
                executed and the protections request write access.

     [EROFS]    The mapped file resides on a read-only file system and the
                protections request write access.