CacheFiles: Implement invalidation

Implement invalidation for CacheFiles.  This is in two parts:

 (1) Provide an invalidation method (which just truncates the backing file).

 (2) Abort attempts to copy anything read from the backing file whilst
     invalidation is in progress.

Question: CacheFiles uses truncation in a couple of places.  It has been using
notify_change() rather than sys_truncate() or something similar.  This means
it bypasses a bunch of checks and suchlike that it possibly should be making
(security, file locking, lease breaking, vfsmount write).  Should it be using
vfs_truncate() as added by a preceding patch or should it use notify_write()
and assume that anyone poking around in the cache files on disk gets
everything they deserve?

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

2 files changed, 53 insertions, 1 deletions

diff --git a/fs/cachefiles/interface.c b/fs/cachefiles/interface.c
index 9bff0f878cfd..7a9d574b961c 100644
--- a/fs/cachefiles/interface.c
+++ b/fs/cachefiles/interface.c
@@ -441,6 +441,54 @@ truncate_failed:
 }
 
 /*
+ * Invalidate an object
+ */
+static void cachefiles_invalidate_object(struct fscache_operation *op)
+{
+        struct cachefiles_object *object;
+        struct cachefiles_cache *cache;
+        const struct cred *saved_cred;
+        struct path path;
+        uint64_t ni_size;
+        int ret;
+
+        object = container_of(op->object, struct cachefiles_object, fscache);
+        cache = container_of(object->fscache.cache,
+                             struct cachefiles_cache, cache);
+
+        op->object->cookie->def->get_attr(op->object->cookie->netfs_data,
+                                          &ni_size);
+
+        _enter("{OBJ%x},[%llu]",
+               op->object->debug_id, (unsigned long long)ni_size);
+
+        if (object->backer) {
+                ASSERT(S_ISREG(object->backer->d_inode->i_mode));
+
+                fscache_set_store_limit(&object->fscache, ni_size);
+
+                path.dentry = object->backer;
+                path.mnt = cache->mnt;
+
+                cachefiles_begin_secure(cache, &saved_cred);
+                ret = vfs_truncate(&path, 0);
+                if (ret == 0)
+                        ret = vfs_truncate(&path, ni_size);
+                cachefiles_end_secure(cache, saved_cred);
+
+                if (ret != 0) {
+                        fscache_set_store_limit(&object->fscache, 0);
+                        if (ret == -EIO)
+                                cachefiles_io_error_obj(object,
+                                                        "Invalidate failed");
+                }
+        }
+
+        fscache_op_complete(op);
+        _leave("");
+}
+
+/*
  * dissociate a cache from all the pages it was backing
  */
 static void cachefiles_dissociate_pages(struct fscache_cache *cache)
@@ -455,6 +503,7 @@ const struct fscache_cache_ops cachefiles_cache_ops = {
         .lookup_complete        = cachefiles_lookup_complete,
         .grab_object            = cachefiles_grab_object,
         .update_object          = cachefiles_update_object,
+        .invalidate_object      = cachefiles_invalidate_object,
         .drop_object            = cachefiles_drop_object,
         .put_object             = cachefiles_put_object,
         .sync_cache             = cachefiles_sync_cache,
diff --git a/fs/cachefiles/rdwr.c b/fs/cachefiles/rdwr.c
index 93a0815e0498..2c994885520a 100644
--- a/fs/cachefiles/rdwr.c
+++ b/fs/cachefiles/rdwr.c
@@ -174,7 +174,10 @@ static void cachefiles_read_copier(struct fscache_operation *_op)
                 _debug("- copy {%lu}", monitor->back_page->index);
 
         recheck:
-                if (PageUptodate(monitor->back_page)) {
+                if (test_bit(FSCACHE_COOKIE_INVALIDATING,
+                             &object->fscache.cookie->flags)) {
+                        error = -ESTALE;
+                } else if (PageUptodate(monitor->back_page)) {
                         copy_highpage(monitor->netfs_page, monitor->back_page);
                         fscache_mark_page_cached(monitor->op,
                                                  monitor->netfs_page);