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SubjectRe: nfs MAP_SHARED corruption fix
Hi Andrea, Trond,

the demo for the NFS SHARED_MAP corruption:

garloff@daubechies:~/C $ uname -sr
Linux 2.4.4
garloff@daubechies:~/C $ ./test_nfs_shared_map ; head -1 ./testfile; sleep 10; head -1 ./testfile
Linux NFS rocks.
Linux NFS sucks.

Sources attached. I still have to test your fix, Trond.

Kurt Garloff <> Eindhoven, NL
GPG key: See mail header, key servers Linux kernel development
SuSE GmbH, Nuernberg, FRG SCSI, Security
/** test_nfs_shared_map.c
* Creates a file, expands it by ftruncate, mmaps it, writes
* to the mapped memory, unmaps it and closes the file again.
* This triggers a bug in 2.4.4 NFS client code: The file won't
* contain the data written to the mapped memory.
* (c) Kurt Garloff <>, 2001-05-09, GNU GPL

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <errno.h>

const char * const bad = "Linux NFS sucks.\n";
const char * const good = "Linux NFS rocks.\n";
const char * const name = "testfile";

#define LEN 4096

int die (const char* const txt)
perror (txt);
exit (errno);

int main ()
char* adr; int err;
int fd = open (name, O_RDWR | O_CREAT | O_TRUNC, 0644);
if (fd <= 0) die ("create testfile");
err = write (fd, bad, strlen (bad));
close (fd);
truncate (name, LEN);
sync ();
fd = open (name, O_RDWR);
if (fd <= 0) die ("open testfile");
adr = (char*) mmap (0, LEN, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
if (!adr) die ("mmap failed");
strcpy (adr, good);
strcpy (adr+32, good);
msync (adr, LEN, MS_SYNC);
munmap (adr, LEN);
close (fd);
[unhandled content-type:application/pgp-signature]
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