On Mon, 12 May 2008 04:48:00 -0700, Boltar wrote:

> Hi
>
> I have to write an app that will scan a file containing records in fixed
> length fields - perfect for memory mapping. However , I'll also from
> time to time need to write new records onto the end of the file on the
> fly. My question is - is there a way to remap the file or extend the
> size of the mapped segment to include new fields written onto the end
> WITHOUT invaliding the current memory map pointer? (so I don't want to
> just munmap and mmap again).

mremap() is what you need.
Note there is *no guarantee* that the pointer remains the same. The
system _may_ choose another place in your VM-map, if it wants to.
(similar to realloc())

So your program should be designed carefully: don't allow any pointers
inside your mmap()ed area(, or be prepared to abandon or repare them on a
mremap()). Easyest way is to only keep the base-pointer and the mapped
size, and use offsets or indexes for addressing the mmapped area, IMHO.

HTH,
AvK

Boltar wrote:

> I have to write an app that will scan a file containing records in
> fixed length fields - perfect for memory mapping. However , I'll also
> from time to time need to write new records onto the end of the file
> on the fly. My question is - is there a way to remap the file or
> extend the size of the mapped segment to include new fields written
> onto the end WITHOUT invaliding the current memory map pointer? (so I
> don't want to just munmap and mmap again).

I don't think you need to do anything special. Just make sure that you
make the original mapping big enough and don't access the mapping past
the end of the file.

DS