mprotect(2)                      DG/UX 5.4.2                     mprotect(2)


NAME
       mprotect - set memory access for mapping

SYNOPSIS
       #include <sys/types.h>
       #include <sys/mman.h>

       int mprotect(addr, len, prot)
       caddrt addr;
       sizet  len;
       int     prot;

DESCRIPTION
       The DG/UX system provides alternative calls for setting memory
       access: memctl(2), defined by the 88open Binary Compatibility
       Standard (BCS), revision 1.1A; and mprotect(2), defined by the System
       V Interface Definition, Issue 3 (SVID3). If your program must be BCS-
       compliant, use memctl(2).  Otherwise, use mprotect(2) as explained
       below.

       The mprotect(2) call sets access attributes for a designated region
       of memory:

       addr   is the starting address of the memory region.

       len    is the length in bytes of the region.

       prot   is the access attribute, which may be any one or an ORed
              combination of: PROT_READ for read access, PROT_WRITE for
              write access, PROT_EXEC for execute access, or PROT_NONE for
              no access.

       The addr must be a page-aligned address; len is rounded up to the
       next page multiple. To find out the system page size, use sysconf(2)
       with the _SC_PAGESIZE argument. The memory region specified by addr
       and len must all be mapped within the caller's address space.

       Read and execute access are not guaranteed to be enforced exactly as
       specified in prot. For example, write access is often implemented as
       read-write (PROTREAD | PROTWRITE), rather than as simply write
       (PROTWRITE). However, write access is always denied unless prot
       includes PROTWRITE. Also, no access is allowed if prot is PROTNONE.

       On M88000 systems such as the AViiON, programs that modify and
       execute memory need to invoke csync(2) just after the modification
       and prior to the execution.  Doing so notifies the system, and
       synchronizes the contents of memory with that of the caches.

       When several processes share a memory region, note:

       ⊕    Executable mappings of the shared region should include write
            access, to insure that reading is always safe.

       ⊕    At least one of the processes must invoke csync(2), following



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mprotect(2)                      DG/UX 5.4.2                     mprotect(2)


            any modifications by the processes, and preceding execution by
            any of them.

       If mprotect(2) fails, the access attributes for portions of the
       specified memory region may change, while the attributes for other
       portions may not.

ACCESS CONTROL
       In the following two cases, the prot argument must not include write
       (PROTWRITE) access:

       ⊕    One or more pages in the region lie in a shared memory segment
            that was attached using the SHMRDONLY option.

       ⊕    One or more pages in the region have been mapped using mmap(2)
            with the MAPSHARED option, and the file passed to mmap(2) was
            not open for writing.

RETURN VALUE
       Upon successful completion, mprotect() returns a value of 0.
       Otherwise, it returns the value -1, and sets errno to indicate an
       error.

DIAGNOSTICS
       Under the following conditions, mprotect() fails and sets errno to:

       EINVAL         if addr is not a page aligned address.

       EACCES         if prot specifies a protection that violates the
                      access permissions some mapping in the region has to
                      its underlying memory object.

       EAGAIN         if prot specifies PROTWRITE over a locked MAPPRIVATE
                      mapping and there are insufficient memory resources to
                      reserve for locking the private page.

       EAGAIN         if prot specifies PROTWRITE over a MAPPRIVATE
                      mapping and there are insufficient swap space
                      resources to be reserved for possible page
                      modification.

       ENOMEM         if len is equal to zero.

       ENOMEM         if some page in the memory region is not mapped within
                      the caller's address space.

SEE ALSO
       csync(2), memctl(2), mmap(2), shmat(2), sysconf(2).









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