cifs: Fix flushing, invalidation and file size with FICLONE

Fix a number of issues in the cifs filesystem implementation of the FICLONE
ioctl in cifs_remap_file_range().  This is analogous to the previously
fixed bug in cifs_file_copychunk_range() and can share the helper
functions.

Firstly, the invalidation of the destination range is handled incorrectly:
We shouldn't just invalidate the whole file as dirty data in the file may
get lost and we can't just call truncate_inode_pages_range() to invalidate
the destination range as that will erase parts of a partial folio at each
end whilst invalidating and discarding all the folios in the middle.  We
need to force all the folios covering the range to be reloaded, but we
mustn't lose dirty data in them that's not in the destination range.

Further, we shouldn't simply round out the range to PAGE_SIZE at each end
as cifs should move to support multipage folios.

Secondly, there's an issue whereby a write may have extended the file
locally, but not have been written back yet.  This can leaves the local
idea of the EOF at a later point than the server's EOF.  If a clone request
is issued, this will fail on the server with STATUS_INVALID_VIEW_SIZE
(which gets translated to -EIO locally) if the clone source extends past
the server's EOF.

Fix this by:

 (0) Flush the source region (already done).  The flush does nothing and
     the EOF isn't moved if the source region has no dirty data.

 (1) Move the EOF to the end of the source region if it isn't already at
     least at this point.  If we can't do this, for instance if the server
     doesn't support it, just flush the entire source file.

 (2) Find the folio (if present) at each end of the range, flushing it and
     increasing the region-to-be-invalidated to cover those in their
     entirety.

 (3) Fully discard all the folios covering the range as we want them to be
     reloaded.

 (4) Then perform the extent duplication.

Thirdly, set i_size after doing the duplicate_extents operation as this
value may be used by various things internally.  stat() hides the issue
because setting ->time to 0 causes cifs_getatr() to revalidate the
attributes.

These were causing the cifs/001 xfstest to fail.

Fixes: 04b38d60 ("vfs: pull btrfs clone API to vfs layer")
Signed-off-by: David Howells <dhowells@redhat.com>
Cc: stable@vger.kernel.org
cc: Christoph Hellwig <hch@lst.de>
cc: Paulo Alcantara <pc@manguebit.com>
cc: Shyam Prasad N <nspmangalore@gmail.com>
cc: Rohith Surabattula <rohiths.msft@gmail.com>
cc: Matthew Wilcox <willy@infradead.org>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cifs@vger.kernel.org
cc: linux-mm@kvack.org
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>