Re: [PATCH] log replay should not overwrite newer ondisk inodes

Lachlan McIlroy
2007-08-31T02:20:45Z

Timothy Shimmin wrote:
> Timothy Shimmin wrote:
>>>> But I'm not sure this is an error...
>>>> Hmmmm...I'm a bit confused.
>>>> So you are _almost_ combining an error check with a flushiter check?
>>>> If one buffer is an inode magic# and the other isn't then we
>>>> have an error right - and could report it - but we are not doing
>>>> that here.
>>> Not exactly. If what's on disk is not an inode but the log item is
>>> then that could be because we haven't written the inode to disk yet
>>> and we need to perform recovery.
>> Yeah, I was thinking about that afterward.
>> The item's format which gives the blk# for the buf to read could
>> be a block which hasn't been used for an inode yet.
>>
> Well, if what's on disk is not an inode but some other data
> and it happens to have the inode magic# which is remotely possible,
> then we are making a bad assumption.
> i.e. if we're not sure what the block/buffer should be, then testing the
> MAGIC# isn't a guarantee it's an inode then.
> Well not for the freeing of inode clusters case I would assume.
> Or am I missing something?
I don't think you're missing anything!

You're right though - a magic number check is no guarantee. On the same
vein, adding a generation number check isn't much better.