Re: [PATCH v5 9/9] btrfs: btrfs_copy_file_range() only supports reflinks

On Fri, Oct 16, 2015 at 07:49:19AM -0400, Chris Mason wrote:

quoted

Yes, that would be my preference.  I'd also like to understand what
exactly btrfs does in fallocate.

For which part?  The answer changes based on how many references there
are to a given fallocated region.

Both cases.  With btrfs allocating new block on every write how do you
avoid that ENOSPC?  Is there a unassigned block preallocation that's
made persistent in some way?