mmap man page on Ultrix

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mmap(2)								       mmap(2)

Name
       mmap - maps memory of a character device

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

       caddr_t mmap(addr, len, prot, flags, fd, off)
       caddr_t addr;
       size_t len;
       int prot;
       int flags;
       int fd;
       off_t off;

Arguments
       addr	 Specifies  the	 address  space	 of  the calling process where
		 begins mapping the memory associated with the specified char‐
		 acter device.

       len	 Specifies the number of bytes to map.

       prot	 Specifies  the	 protection flag for the mapping.  The protec‐
		 tion flag is the bitwise inclusive OR of these valid  protec‐
		 tion flag bits defined in or

       flags	 Specifies  the mapping flag.  The mapping flag is the bitwise
		 inclusive OR of these valid flag mapping bits defined in or

       fd	 Specifies the file descriptor for the character device	 being
		 mapped.

       off	 Specifies  the	 offset	 in  bytes into the character device's
		 memory.

Description
       The system call maps the memory of a character device (fd) starting  at
       a specified offset (off) for a specified number of bytes (len) into the
       address space of the calling process.  The routine does	not  map  into
       private	data,  stack, or text segments.	 This routine does not replace
       any existing mappings.  All the mapped regions are inherited by a child
       process on a fork.

       When calling you need to:

       ·    Align the offset

	    You	 must align the offset (off) on a page boundary as returned by
	    the system call.

       ·    Indicate the number of bytes to map

	    The number of bytes to map (len) need not be  a  multiple  of  the
	    page  size	as returned by However, will round the value of len to
	    the nearest multiple of the page size as returned by  and  perform
	    the mapping over whole pages.

       ·    Specify the protection for the mapping

	    You specify the protection for the mapping by ORing the prot argu‐
	    ment with one or more of the constants or If you specify only both
	    VAX and RISC architectures will grant read access.	If you specify
	    only then both VAX and RISC	 architectures	will  grant  read  and
	    write access.

       ·    Indicate the address at which the mapping occurs

	    The	 addr  and flags arguments are used by to determine the actual
	    address at which the mapping is done.   You	 specify  the  mapping
	    flag by ORing the flags argument with one or more of the constants
	    or

	    Based on the values you specify for addr and flags,	 performs  the
	    mapping as follows:

       -	      If  addr	is equal to zero, selects the address at which
		      the mapping is done.

       -	      If addr is not equal to zero and you specified the  map‐
		      ping  is done at the address specified in addr.  You can
		      obtain the boundary on which addr	 must  be  aligned  by
		      calling the system call.

       -	      If addr is not equal to zero and you did not specify the
		      mapping is done at  the  address	rounded	 down  to  the
		      boundary	returned  by The value returned by is machine-
		      dependent.

Restrictions
       You must observe the following restrictions when calling

       ·    Maximum number of mapped regions for each process

	    The shared memory functionality upon which is implemented requires
	    that  you  not exceed the maximum number of shared memory segments
	    allowed for each process.  The default value is six shared	memory
	    segments  for each process.	 You can configure (in the system con‐
	    figuration file) the number of shared  memory  segments  for  each
	    process by using the constant

       ·    Maximum number of mapped regions on the system

	    The	 shared	 memory	 functionality	imposes a limit on the maximum
	    number of mapped regions on the system.  The default limit is 100,
	    sufficient	to support a maximum configuration of all devices that
	    can be mapped.  The maximum configuration is 2*21 devices  (2  VME
	    adapters, 21 devices for each bus).

       ·    A process mapping the same region of device memory

	    A  process	cannot	map the same region of device memory more than
	    once into its address space.  This limitation is a result  of  the
	    lack  of multiple attach capability for shared memory.  However, a
	    single process can map different regions of device memory simulta‐
	    neously into its address space.  Two regions of memory are identi‐
	    cal only if they start at the same offset in device memory and are
	    of the same length.

       ·    Use of the system call

	    The system call does not work on the addresses mapped by a call to
	    The reason is that does not work for shared memory	and  therefore
	    cannot  be	used to change protection for the address space mapped
	    by

Return Value
       If successful, returns the address where the mapping was done.	Other‐
       wise,  it  returns  -1 and sets the errno argument to one of the errors
       listed in the Diagnostics section.

Diagnostics
       The call to fails if one or more of the following is true:

       [EBADF]	 The device, represented by the file  descriptor  fd,  is  not
		 open.

       [EACCES]	 The  device,  represented  by	the file descriptor fd, is not
		 open for read operations and  you  specified  the  protection
		 flag  in  prot.   Or, the device is not open for write opera‐
		 tions and you specified the protection flag in prot.

       [ENXIO]	 Addresses in the range [ off, off + len  ]  are  invalid  for
		 this device, represented by the file descriptor fd.

       [EINVAL]	 You did not specify either or in the flags argument.

       [EINVAL]	 You did not specify either or in the prot argument.

       [EINVAL]	 The file descriptor, fd, is not a valid file descriptor for a
		 character device.

       [ENODEV]	 The file descriptor, fd, refers to a  device  that  does  not
		 support the system call.

       [ENOMEM]	 There	is not enough room in the address space to perform the
		 mapping.

See Also
       getpagesize(2), getsysinfo(2), mmapalignment(1), munmap(2)

								       mmap(2)
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