e2fsprogs/debugfs/write: Input/output error when file size is zero

[Robert Yang <liezhi.yang@windriver.com>]

Hello experts,

I met a "Input/output error" problem when used debugfs' command "write"
to copy a zero size file to ext4 fs, here are the steps to reproduce the
problem:

$ dd if=/dev/zero of=test.img count=1M bs=1k
$ mkfs.ext4 -F test.img
$ touch emptyfile
$ debugfs -R "write emptyfile emptyfile" -w test.img
$ mkdir mnt
$ mount test.img mnt/
$ ls mnt/emptyfile
ls: cannot access mnt/emptyfile: Input/output error

The degbufs is from the up-to-date git repo, the ext2 and ext3 work well,
I think that it is caused by the EXT4_EXTENTS_FL, it works well if we
turn off the EXT4_EXTENTS_FL when the file size is zero, but this is not
a correct fix, would you please give me some instructions so that I can
fix it?

-- 
Thanks

Robert