linux-ext4 - Re: [PATCH v3 12/13] docs: Add fast commit documentation

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Message-Id: <C41A9852-DFA0-4F1A-A984-29A71D23CEFB@dilger.ca>
Date:   Fri, 18 Oct 2019 13:51:56 +0900
From:   Andreas Dilger <adilger@...ger.ca>
To:     "Theodore Y. Ts'o" <tytso@....edu>
Cc:     Harshad Shirwadkar <harshadshirwadkar@...il.com>,
        linux-ext4@...r.kernel.org
Subject: Re: [PATCH v3 12/13] docs: Add fast commit documentation

What about rename or hard link?

Cheers, Andreas

> On Oct 18, 2019, at 10:56, Theodore Y. Ts'o <tytso@....edu> wrote:
> 
>> On Tue, Oct 01, 2019 at 12:41:01AM -0700, Harshad Shirwadkar wrote:
>> +
>> +Multiple fast commit blocks are a part of one sub-transaction. To
>> +indicate the last block in a fast commit transaction, fc_flags field
>> +in the last block in every subtransaction is marked with "LAST" (0x1)
>> +flag. A subtransaction is valid only if all the following conditions
>> +are met:
>> +
>> +1) SUBTID of all blocks is either equal to or greater than SUBTID of
>> +   the previous fast commit block.
>> +2) For every sub-transaction, last block is marked with LAST flag.
>> +3) There are no invalid blocks in between.
> 
> I'm wondering why we need to support multiple inodes being modified in
> a single transaction.  As we currently have defined what can be done,
> all updates to an inode should be free standing and not dependent on a
> change to another inode, right?  And today, one block only modifies
> one inode.
> 
> The only reason why we might want to define a sub-transaction as being
> composed of multiple inodes, which must all be updated in an
> all-or-nothing fashion, is the swap boot inode ioctl, and if that's
> the only one, I wonder if it's worth the extra complexity.
> 
> Am I missing anything?
> 
>                    - Ted