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Update the mmap.2 and minherit.2 manual pages. Add a short explanation and

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referal from mmap to minherit for MAP_INHERIT.  Fully document the
minherit.2 manual page (because frankly, my dear, however you think it
currently works is almost certainly wrong!).  I may soon re-implement
MAP_COPY because I believe we can support it properly now, but I will have
to call it something else and that is for a later time.
This commit is contained in:
Matthew Dillon 2001-08-24 19:28:00 +00:00
parent c45da89917
commit dbad546ba7
2 changed files with 40 additions and 0 deletions
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34
lib/libc/sys/minherit.2
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@ -55,6 +55,36 @@ changes the specified pages to have the inheritance characteristic
Not all implementations will guarantee that the inheritance characteristic
can be set on a page basis;
the granularity of changes may be as large as an entire region.
.Fx
is capable of adjusting inheritance characteristics on a page basis.
Inheritance only effects children created by
.Fn fork .
It has no effect on
.Fn exec .
exec'd processes replace their address space entirely. This function also
has no effect on the parent's address space (other then to potentially
share the address space with its children).
.Pp
Inheritance is a rather esoteric feature largely superceeded by the
MAP_SHARED feature of
.Fn mmap .
However, it is possible to use
.Fn minherit
to share a block of memory between parent and child that has been mapped
MAP_PRIVATE. That is, modifications made by parent or child are shared but
the original underlying file is left untouched.
.Bl -tag -width MAP_HASSEMAPHORE
.It Dv MAP_SHARED
This option causes the address space in question to be shared between
parent and child. It has no effect on how the original underlying backing
store was mapped.
.It Dv MAP_PRIVATE
This option prevents the address space in question from being inherited
at all. The address space will be unmapped in the child.
.It Dv MAP_COPY
This option has been deprecated. It had the same effect as MAP_PRIVATE,
which is not what one would expected for an option called MAP_COPY.
.El
.Sh RETURN VALUES
.Rv -std minherit
.Sh ERRORS
@ -78,6 +108,10 @@ and
.Fa len
arguments.
.El
.Sh BUGS
Once you set inheritance to MAP_PRIVATE or MAP_SHARED, there is no way to
recover the originanl copy-on-write semantics short of unmapping and remapping
the area.
.Sh SEE ALSO
.Xr fork 2 ,
.Xr madvise 2 ,

6
lib/libc/sys/mmap.2
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@ -128,6 +128,11 @@ Use of this option is discouraged.
.It Dv MAP_HASSEMAPHORE
Notify the kernel that the region may contain semaphores and that special
handling may be necessary.
.It Dv MAP_INHERIT
This flag never operated as advertised and is no longer supported.
Please refer to
.Xr minherit 2
for further information.
.It Dv MAP_NOCORE
Region is not included in a core file.
.It Dv MAP_NOSYNC
@ -318,6 +323,7 @@ was specified and insufficient memory was available.
.El
.Sh SEE ALSO
.Xr madvise 2 ,
.Xr minherit 2 ,
.Xr mincore 2 ,
.Xr mlock 2 ,
.Xr mprotect 2 ,