Re: nfs MAP_SHARED corruption fix

[Kurt Garloff <garloff@suse.de>]

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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.

Regards,
-- 
Kurt Garloff  <garloff@suse.de>                          Eindhoven, NL
GPG key: See mail header, key servers         Linux kernel development
SuSE GmbH, Nuernberg, FRG                               SCSI, Security

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/** 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 <garloff@suse.de>, 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);
#ifdef NEED_MSYNC
	msync (adr, LEN, MS_SYNC);
#endif
	munmap (adr, LEN);
	close (fd);
}

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