On 02/04/2012 12:04 PM, Eric Sandeen wrote:
Now that ext4, xfs,& ocfs2 can support punch hole, a tool to
"re-sparsify" a file by punching out ranges of 0s might be in order.
I whipped this up fast, it probably has bugs& off-by-ones but thought
I'd send it out. It's not terribly efficient doing 4k reads by default
I'll see if util-linux wants it after it gets beat into shape.
(or did a tool like this already exist and I missed it?)
(Another mode which does a file copy, possibly from stdin
might be good, like e2fsprogs/contrib/make-sparse.c ? Although
that can be hacked up with cp already).
It works like this:
[root@inode sparsify]# ./sparsify -h
Usage: sparsify [-m min hole size] [-o offset] [-l length] filename
So I have a similar tool queued up in ocfs2-tools. Named puncher.
I'll pull it out if we get something in util-linux. But maybe you can
extract something useful from it.
Like.... maybe doing dry-run as default. It is an inplace modification
after all. Also using a large hole size as default (1MB). Over using
hole punching will negatively affect read performance. We should make
the sane choice for the user.
On a related note, it may make sense for ext4 to populate the cluster
size (bigalloc) in stat.st_blksize.