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Subject[CHECKER] ext3 bug in ftruncate() with O_SYNC?
From
Date
Hi.  We're doing some checking on Linux file systems and found
what appears to be a bug in the Linux 2.6.11 implementation of
ext3: when ftruncate shrinks a file, using a file descriptor
opened with O_SYNC, the file size is not updated synchronously.
I've appended a test program that illustrates the problem. After
this program runs, the file system shows a file with length 1031,
not 4 as would be expected if the ftruncate completed
synchronously. (If I insert an fsync before closing the file,
the file length is correct.)

Does this look like a bug to you guys?

Thanks,

Ben.

----------------------------------------------------------------------

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <assert.h>

#define CHECK(ret) if(ret < 0) {perror(0); assert(0);}

int systemf(const char *fmt, ...)
{
static char cmd[1024];

va_list ap;
va_start(ap, fmt);
vsprintf(cmd, fmt, ap);
va_end(ap);

fprintf(stderr, "running cmd \"%s\"\n", cmd);
return system(cmd);
}

main(int argc, char *argv[])
{
int ret, fd;
systemf("umount /dev/sbd0");
systemf("sbin/mkfs.ext3 -F -j -b 1024 /dev/sbd0 2048");
systemf("sbin/e2fsck.shared -y /dev/sbd0");
systemf("mount -t ext3 /dev/sbd0 /mnt/sbd0 -o commit=65535");
systemf("umount /dev/sbd0");
systemf("mount -t ext3 /dev/sbd0 /mnt/sbd0 -o commit=65535");

fd = open("/mnt/sbd0/0001", O_CREAT | O_RDWR | O_SYNC, 0700);
CHECK(fd);
ret = write(fd, "foobar", 6);
CHECK(ret);
ret = ftruncate(fd, 1031);
CHECK(ret);
ret = pwrite(fd, "bazzle", 6, 1031 - 6);
CHECK(ret);
ret = ftruncate(fd, 4);
CHECK(ret);
ret = close(fd);
CHECK(ret);

#if 0
{
#include "../sbd/sbd.h"
int sbd_fd = open("/dev/sbd0", O_RDONLY);
ret = ioctl(sbd_fd, SBD_COPY_DISK, 1);
CHECK(ret);
close(sbd_fd);
}
#else
systemf("reboot -f -n");
#endif
return 0;
}



--
Ben Pfaff
email: blp@cs.stanford.edu
web: http://benpfaff.org
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