linux-kernel - Re: Proposal for "proper" durable fsync() and fdatasync()

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 26 Feb 2008 17:00:11 +0000
From:	Jamie Lokier <jamie@...reable.org>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Chris Wedgwood <cw@...f.org>
Subject: Re: Proposal for "proper" durable fsync() and fdatasync()

Jeff Garzik wrote:
> Nick Piggin wrote:
> >Anyway, the idea of making fsync/fdatasync etc. safe by default is
> >a good idea IMO, and is a bad bug that we don't do that :(
> 
> Agreed...  it's also disappointing that [unless I'm mistaken] you have 
> to hack each filesystem to support barriers.
> 
> It seems far easier to make sync_blkdev() Do The Right Thing, and 
> magically make all filesystems data-safe.

Well, you need ordered metadata writes, barriers _and_ flushes with
some filesystems.

Merely writing all the data pages than issuing a drive cache flush
won't Do The Right Thing with those filesystems - someone already
mentioned Btrfs, where it won't.

But I agree that your suggestion would make a superb default, for
filesystems which don't provide their own function.

It's not optimal even then.

  Devices: On a software RAID, you ideally don't want to issue flushes
  to all drives if your database did a 1 block commit entry.  (But they
  probably use O_DIRECT anyway, changing the rules again).  But all that
  can be optimised in generic VFS code eventually.  It doesn't need
  filesystem assistance in most cases.

  Apps: don't always want a full flush; sometimes a barrier would do.

-- Jamie
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/