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>
diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
index 907bb56..5db5000 100644
--- a/include/linux/fscache-cache.h
+++ b/include/linux/fscache-cache.h
@@ -395,6 +395,7 @@
struct rb_node objlist_link; /* link in global object list */
#endif
pgoff_t store_limit; /* current storage limit */
+ loff_t store_limit_l; /* current storage limit */
};
extern const char *fscache_object_states[];
@@ -439,6 +440,7 @@
object->events = object->event_mask = 0;
object->flags = 0;
object->store_limit = 0;
+ object->store_limit_l = 0;
object->cache = cache;
object->cookie = cookie;
object->parent = NULL;
@@ -491,6 +493,7 @@
static inline
void fscache_set_store_limit(struct fscache_object *object, loff_t i_size)
{
+ object->store_limit_l = i_size;
object->store_limit = i_size >> PAGE_SHIFT;
if (i_size & ~PAGE_MASK)
object->store_limit++;