Pls Help: How to write immediately to crypted fs? (cryptoloop)

Hi,

I use the cryptoloop via the losetup (with twofish) to encrypt a
partition. Within the encrypted partition I use the ext3 fs, which
I've "tuned" with commit=<x>, data=journal, mounted with -o sync etc.

But nevertheless the time until a write() from my application is on
the disk can be up to 30 seconds?!?! Even a subsequent fsync() from
the app doesn't has any effect.

So, what happens is like this:

1. losetup /dev/hdaX /dev/loop1 (w/ twofish)
2. mke2fs -t ext3 /dev/loop1
3. mount /dev/loop1 /home
4. Start App
5. fd = open(/home/file.dat)
6. write(fd, data)
[6a. fsync(fd)]
7. close(fd)
8. Leave App
...
9. Wait up to X seconds
10. de-energize the system
11. Power-on, boot again
12. /home/file.dat is like before 4.

Is this normal??? How can I reduce the time to near null?

I think, the lap must be in (?) the loopdevice, because on a plain
ext3 partition it seems to work (write immediately).

Thanks in advance,
Thorben

Thorben Suhr wrote:
> Hi,
>
> I use the cryptoloop via the losetup (with twofish) to encrypt a
> partition. Within the encrypted partition I use the ext3 fs, which
> I've "tuned" with commit=<x>, data=journal, mounted with -o sync etc.
>
> But nevertheless the time until a write() from my application is on
> the disk can be up to 30 seconds?!?! Even a subsequent fsync() from
> the app doesn't has any effect.
>
> So, what happens is like this:
>
> 1. losetup /dev/hdaX /dev/loop1 (w/ twofish)
> 2. mke2fs -t ext3 /dev/loop1
> 3. mount /dev/loop1 /home
> 4. Start App
> 5. fd = open(/home/file.dat)
> 6. write(fd, data)
> [6a. fsync(fd)]
> 7. close(fd)
> 8. Leave App
> ...
> 9. Wait up to X seconds
> 10. de-energize the system
> 11. Power-on, boot again
> 12. /home/file.dat is like before 4.
>
> Is this normal??? How can I reduce the time to near null?

Go back and re-read the man page for the open system call (man 2 read).
Pay special attention to the comments about the flags O_SYNC,
O_DIRECT, and the restrictions on their use.