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List:       yaffs
Subject:    [Yaffs] Renaming an open file causes it to be truncated on reboot
From:       Laurence Withers <l () lwithers ! me ! uk>
Date:       2006-08-17 10:25:59
Message-ID: 200608171125.59948.l () lwithers ! me ! uk
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Hi,

Recently, I uncovered a problem on a yaffs1 filesystem where calling rename() 
on an open file and then closing the file would cause the contents to be lost 
on a reboot (or presumably on remounting the filesystem).

I've attached a testcase which consistently shows the problem.

The userspace workaround is to close the file before renaming it.

Bye for now,
-- 
Laurence Withers                              http://www.lwithers.me.uk/
mailto:l@lwithers.me.uk   tel:+447753988197  jabber:l.withers@jabber.org

["renametest.c" (text/x-csrc)]

#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <string.h>

/* problem occurs when rename occurs before close, but not after */
#define RENAME_BEFORE_CLOSE

const char* tmp = "/etc/foo.bar.baz.quux";
const char* target = "/etc/dssserver.cfg";

int main(void)
{
	int fd;
	char tmpbuf[4096];
	ssize_t rd;

	fd = open(tmp, O_WRONLY | O_CREAT | O_EXCL, 0644);
	if(fd == -1) {
		perror("open");
		return -1;
	}

	if(write(fd, "fob", 3) != 3) {
		perror("write");
		return -1;
	}

#ifdef RENAME_BEFORE_CLOSE
	if(rename(tmp, target)) {
		perror("rename");
		return -1;
	}
#endif

	fsync(fd);
	if(close(fd)) {
		perror("close");
		return -1;
	}

#ifndef RENAME_BEFORE_CLOSE
	if(rename(tmp, target)) {
		perror("rename");
		return -1;
	}
#endif

	fd = open(target, O_RDONLY);
	if(fd == -1) {
		perror("open");
		return -1;
	}

	while(1) {
		rd = read(fd, tmpbuf, sizeof(tmpbuf));
		switch(rd) {
		case -1:
			perror("read");
			return -1;

		case 0:
			printf("\nEOF\n");
			close(fd);
			return 0;

		default:
			printf("%.*s", rd, tmpbuf);
			break;
		}
	}
}



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