Re: [PATCH] Btrfs: allow file data clone within a file

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On Sun, Apr 07, 2013 at 10:18:18PM +0800, Liu Bo wrote:
> We did not allow file data clone within the same file because of
> deadlock issues.
>
> However, we now use nested lock to avoid deadlock between the
> parent directory and the child file.
> 
> So it's safe to do file clone at different offset within the
> same file.

There's a todo comment inside the function saying that cloning within
the same file is possible but with an exception of overlapping ranges.
How does your patch prevent that? With current code + your patch it's
possible to call 

2583         /* truncate page cache pages from target inode range */
2584         truncate_inode_pages_range(&inode->i_data, destoff,
2585                                    PAGE_CACHE_ALIGN(destoff + len) - 1);

where [destoff, destoff+len) intersects with the source [off, off+len)
thus destroying the data to be cloned.

david
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