Re: Linux 2.6.29

Bodo Eggert
2009-03-25T15:20:11Z

Theodore Tso <tytso@mit.edu> wrote:

> OK, so there are a couple of solutions to this problem. One is to use
> ext4 and delayed allocation. This solves the problem by simply not
> allocating the blocks in the first place, so we don't have to force
> them out to solve the security problem that data=ordered was trying to
> solve. Simply mounting an ext3 filesystem using ext4, without making
> any change to the filesystem format, should solve the problem.

[...]

> However, these days, nearly all Linux boxes are single user machines,
> so the security concern is much less of a problem. So maybe the best
> solution for now is to make data=writeback the default. This solves
> the problem too. The only problem with this is that there are a lot
> of sloppy application writers out there, and they've gotten lazy about
> using fsync() where it's necessary;

The problem is not having accidential data loss because the inode /happened/
to be written before the data, but having /guaranteed/ data loss in a
60-seconds-window. This is about as acceptable as having a filesystem
replace _any_ data with "deadbeef" on each crash unless fsync was called.

Besides that: If the problem is due to crappy VM writeout (is it?), reducing
security to DOS level is not the answer. You'd want your fs to be usable on
servers, wouldn't you?