MMAP(2)                 COMMAND REFERENCE                 MMAP(2)



NAME
     mmap - map pages of memory

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

     mmap(pid, fromaddr, toaddr, len, prot, share)
     int pid;
     caddrt fromaddr, toaddr;
     uint len, prot, share;

DESCRIPTION
     The mapping routine mmap allows a process to access areas of
     other processes through its own address space.  It causes
     the calling process' pages starting at toaddr and continuing
     for len bytes to map onto the process with id pid, starting
     at the object's pages fromaddr.

     If pid is M_SELF, an area of the process is mapped to
     itself.  If pid is M_PHYS, an area of the process is mapped
     to physical memory (in which case share is ignored).  If pid
     is M_ZFILL, an area of the process is made "zero-fill-on-
     demand" (in which case fromaddr and share are ignored).  If
     pid is M_NFILL, an area of the process is made "provide-on-
     demand" (in which case fromaddr and share are ignored).

     If the parameter share is true, both mappings will share the
     same memory.  Otherwise, a private copy of the area is made,
     and changes through one mapping are not visible through the
     other.

          PRIVATE   make a private copy for the new mapping
          SHARED    share the area between the mappings

     The parameter prot specifies the accessibility of the pages
     through the new mapping.  Read and write access may be given
     on the basis of processes of the same user, same process
     group, same group, and world.  A process may also protect
     its pages against itself.  The protection for a page is
     specified by or'ing together the following values.

     M_R_SELF       read, process
     M_W_SELF       write, process
     M_R_USER       read, user
     M_W_USER       write, user
     M_R_PGROUP     read, process group
     M_W_PGROUP     write, process group
     M_R_GROUP      read, group
     M_W_GROUP      write, group
     M_R_WORLD      read, world
     M_W_WORLD      write, world



Printed 10/17/86                                                1

MMAP(2)                 COMMAND REFERENCE                 MMAP(2)



     Note that the protection is associated with the mapping, and
     not with the actual memory.

     If the process must change the protection of a mapping, it
     may map the area to itself, with the new protection.  Doing
     this with share cleared will disassociate the area with all
     other mappings.

     The terms "zero-fill-on-demand" and "provide-on-demand" used
     above refer to the handling of pages in mappings which have
     no initial contents.  UTek does not allocate physical memory
     or swap space to such a page until the first reference
     (demand) for that page.  If M_ZFILL is selected, the page is
     filled with zeros before the first reference is satisfied.
     This provides a standard initial value for data regions,
     which is expected by some software.  If M_NFILL is selected,
     the page is not initilized before the first reference is
     satisfied.  This provides a small reduction in overhead in a
     very small number of memory management intensive programs.
     It is highly recommended that this option not be used unless
     a clear advantage is apparent.

     The toaddr, fromaddr and len parameters must be multiples of
     the system cluster size (found using the getpagesize(2)
     call).

DIAGNOSTICS
     Mmap will fail when one of the following occurs:

     [EINVAL]
         An address is not on a cluster boundary or len is not
         positive.

     [EMCOLLIDE]
         Portions of the new area are already mapped.

     [EMRANGE]
         An area is outside the possible user's address space or
         includes part of the uarea.

     [EACCES]
         The required permissions (for reading and/or writing)
         are denied for the named file or area of a process.

     [ESRCH]
         No process can be found corresponding to the specified
         pid.

     [EPERM]
         The area of the object to be mapped is protected against
         the desired operation.




Printed 10/17/86                                                2

MMAP(2)                 COMMAND REFERENCE                 MMAP(2)



RETURN VALUE
     Upon successful completion, a value of 0 is returned.
     Otherwise, a value of -1 is returned and errno is set to
     indicate the error.

CAVEATS
     Since the M_NFILL option opens a security hole, it may not
     be enabled in all versions of UTek.  If it is not enabled,
     it is treated the same as M_ZFILL.

     The M_NFILL symbol may not be available in versions of UTek
     which do not enable its function.

SEE ALSO
     getpagesize(2), mremap(2), munmap(2).








































Printed 10/17/86                                                3

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