Hi Ted,
Thanks for your comments.

First of all, explicit comparisons against the current uid is bad.  A
non-root user might have read/write access to the raw device where a
file sysem is located.  It's bad to encode an assumption one way or
another into a userspace program.  Secondly, whenever a userspace progam
is explicitly trying to encode permission checking, that's a red flag.

I will fix it.

I'm not sure why checking to see if a file's st_uid matches the
current_uid has any validity at all.

e4defrag tries to change the location of data blocks, so I assumed that
non-root users should execute e4defrag only to their file. It would be better
that users who have read/write permission can e4defrag to the file.

What really matters are the number of extents which are non-tail
extents, and smaller than some threshold (probably around 256 MB for
most HDD's), and not forced by skips in the logical block numbering
(i.e., caused by a file being sparse).  The basic idea here is to go
back to why fragments are bad, which is that they slow down file access.
If every few hundred megabytes, you need to seek to another part of the
disk, it's really not the end of the world.

What does 256MB mean? If "some threshold" means the maximum size of one extent,
I think the size is 128MB.

There's a more general question which is I'm not sure how much the
functionality of e4dfrag -c really belongs in e4defrag.  I'm thinking
perhaps that perhaps this functionality should instead go in filefrag,
and/or in e2fsck, which can do the job much more efficiently since it by
definition has direct access to the file system, so it can scan the
inode tables in order.

Currently, e2fsprogs has two commands that report how badly fragmented
a file might be. So, it is smart for e2fsprogs to drop -c option from e4defrag.
e4defrag -c shows whether we need to execute e4defrag or not. For this, I think
we should add "fragmentation score" included in e4defrag -c to the output of
filefrag.

However, sometimes we want to check the fragmentation not only for a single file
but also for many files in the same directory. e4defrag -c gets the extent
information of all files in a directory, and calculates the fragmentation score
based on this information. But I'm not sure that I should add this feature
to filefrag by adding new option or some other way.

Regards,
Kazuya Mio