how does mmap() work?

["Steve Richter" <srichter@xxxxxxxxxxxxx>]

hola,

 

What I think I know:

 

The mmap( ) function is used to map a stream file into memory.

 

The func rcvs an offset into the file and the length of bytes to be mapped. It returns a ptr to the start of the mapped memory.

    char* pData ;

    dword nNbrBytesToMap = 17Meg ;

    pData = mmap( NULL, nNbrBytesToMap, , , FileHandle, OfsIntoFile ) ;

 

The ptr can then be used to write to the stream file:

    pData[17,000,000] = 'x' ;  /* copies 'x' to offset 17 million into the stream file */

 

Multiple jobs can map the same stream file at the same time. The end result being a perm shared space that exceeds the 16 mem space size limit.

 

My questions:

 

How is mapped memory implemented? 

 

What chgs to the architecture, virtual memory manager were needed to be able to do this?

 

Are teraspaces implemented the same way?

 

 

Just asking,

 

Steve Richter