Re: Question on fallocate/ftruncate sequence

[Eric Sandeen <sandeen@redhat.com>]

Frank Mayhar wrote:
> On Tue, 2009-07-21 at 15:54 -0600, Andreas Dilger wrote:

...

>> That said, we might need to have some kind of flag in the on-disk
>> inode to indicate that it was preallocated beyond EOF.  Otherwise,
>> e2fsck will try and extend the file size to match the block count,
>> which isn't correct.  We could also use this flag to determine if
>> truncate needs to be run on the inode even if the new size is the
>> same.
> 
> After chatting with Curt about this today, it sounds like this needs two
> things.  One is your flag in the on-disk inode, set in fallocate() to
> indicate that it has an allocation past EOF.  E2fsck would use this to
> avoid "fixing" the file size to match the block count.  Truncate would
> use this to notice that there are blocks allocated past i_size and get
> rid of them.  It would be cleared by truncate or by ext4_get_blocks when
> using the last block of such an allocation.
> 
> Does this make sense?  Have I missed anything?

I guess I'm not totally sold on the new on-disk flag; we can work out
blocks past EOF w/o needing a new flag can't we?

-eric