linux-ext4 - Re: Atomic non-durable file write API

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Message-ID: <AANLkTimsTF7dvf6yMpkZjJG0HE=cZ0czLyc-Pjjuo_r=@mail.gmail.com>
Date:	Sun, 26 Dec 2010 19:26:23 +0100
From:	Olaf van der Spek <olafvdspek@...il.com>
To:	Boaz Harrosh <bharrosh@...asas.com>
Cc:	Nick Piggin <npiggin@...il.com>, "Ted Ts'o" <tytso@....edu>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-ext4@...r.kernel.org
Subject: Re: Atomic non-durable file write API

On Sun, Dec 26, 2010 at 5:27 PM, Boaz Harrosh <bharrosh@...asas.com> wrote:
>> Are you proposing to turn every single file into a symlink?
>
> Sure, a symlink and a "versioned" file for every object. Something similar
> to the silly rename of nfs.
>
> Even if you have 1000 files that need the same atomicity treatment
> that's not that bad. You should be able to devise a namespace policy
> that makes all this nit and tidy.

Nearly all files on the system need the atomicity treatment.

>> How would that solve the meta-data issue?
>>
>
> That's what I asked. Do you want to preserve the original's file
> metat-data, or the meta-data of the owner of the new content?
> In the first case you'll need a metat-data copy like tar is
> using.

The original meta-data, of course. Including file owner. AFAIK not
doable without root access.

>> Olaf
>
> The point is to fsync/fdatasync on a background thread and continue
> from there where the application is free to go on to the next step.

Not if it's the last thing a process does and another processes is
waiting on it.

> As if you had a notification when the commit was done (in the background).
> So you make it an async pipeline model. The version-naming schem is so the
> pipeline can get arbitrary big.
>
> Boaz
>
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