From: David Howells <dhowells@redhat.com>
Date: Thu, 19 Nov 2009 18:11:52 +0000 (+0000)
Subject: CacheFiles: Don't write a full page if there's only a partial page to cache
X-Git-Tag: v2.6.32~58^2~8
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a17754fb8c28af19cd70dcbec6d5b0773b94e0c1;p=pandora-kernel.git

CacheFiles: Don't write a full page if there's only a partial page to cache

cachefiles_write_page() writes a full page to the backing file for the last
page of the netfs file, even if the netfs file's last page is only a partial
page.

This causes the EOF on the backing file to be extended beyond the EOF of the
netfs, and thus the backing file will be truncated by cachefiles_attr_changed()
called from cachefiles_lookup_object().

So we need to limit the write we make to the backing file on that last page
such that it doesn't push the EOF too far.

Also, if a backing file that has a partial page at the end is expanded, we
discard the partial page and refetch it on the basis that we then have a hole
in the file with invalid data, and should the power go out...  A better way to
deal with this could be to record a note that the partial page contains invalid
data until the correct data is written into it.

This isn't a problem for netfs's that discard the whole backing file if the
file size changes (such as NFS).

Signed-off-by: David Howells <dhowells@redhat.com>
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