linux-kernel - Concerning a post that you made about expandable anonymous shared mappings

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Message-ID: <468562F6.4010604@gmail.com>
Date:	Fri, 29 Jun 2007 14:52:22 -0500
From:	William Tambe <tambewilliam@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Concerning a post that you made about expandable anonymous shared
 mappings

I read a post that you made about not being able to expand anonymous 
shared mapping with mremap(). And I am actually having that issue now.

You made the post in 2004 and we are now in 2007. I would like to know 
if that feature was added because the code below always fail with bus 
error on my machine. I use glibc 2.5

Thank you for helping.

#define _GNU_SOURCE
#include <sys/mman.h>
#include <unistd.h>

#include <stdio.h>

main() {
         void *ptr;
         if ((ptr=mmap(0, 4096, PROT_READ|PROT_WRITE,
                 MAP_ANONYMOUS|MAP_SHARED|MAP_GROWSDOWN, 0, 0)) == -1) {
                 printf("failed to mmap\n");
                 return;
         }

         if ((ptr=mremap(ptr, 4096, 8192, MREMAP_MAYMOVE)) == -1) {
                 printf("failed to mremap\n");
                 return;
         }

         //why does this failed. I am well in the interval [4096, 8192]
         *(unsigned int *)(ptr + 4096 + 8)= 10;
}
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