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.\"	@(#)mimmutable.2	8.1 (Berkeley) 6/9/93
.\"
.Dd $Mdocdate: January 21 2024 $
.Dt MIMMUTABLE 2
.Os
.Sh NAME
.Nm mimmutable
.Nd control the immutability of pages
.Sh SYNOPSIS
.In sys/mman.h
.Ft int
.Fn mimmutable "void *addr" "size_t len"
.Sh DESCRIPTION
The
.Fn mimmutable
system call
changes currently mapped pages in the region to be marked immutable,
which means their protection or mapping may not be changed in the future.
Most requests to
.Xr madvise 2 ,
.Xr minherit 2 ,
.Xr mmap 2 ,
.Xr mprotect 2 ,
.Xr msync 2 , and
.Xr munmap 2
to pages marked immutable will return with error
.Er EPERM .
.Pp
Unmapped pages in the region do not retain immutability, but this
behaviour should not be relied upon.
.Pp
Not all implementations will guarantee that the immutable characteristic
can be set on a page basis;
the granularity of changes may be as large as an entire region.
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
The
.Fn mimmutable
system call will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The virtual address range specified by the
.Fa addr
and
.Fa len
arguments is not valid.
.It Bq Er EPERM
At least one page has inheritance of
.Dv MAP_INHERIT_ZERO .
.El
.Sh SEE ALSO
.Xr minherit 2 ,
.Xr mmap 2 ,
.Xr mprotect 2 ,
.Xr munmap 2
.Sh HISTORY
The
.Fn mimmutable
function first appeared in
.Ox 7.3 .