FS-Cache: Add interface to check consistency of a cached object

Extend the fscache netfs API so that the netfs can ask as to whether a cache
object is up to date with respect to its corresponding netfs object:

	int fscache_check_consistency(struct fscache_cookie *cookie)

This will call back to the netfs to check whether the auxiliary data associated
with a cookie is correct.  It returns 0 if it is and -ESTALE if it isn't; it
may also return -ENOMEM and -ERESTARTSYS.

The backends now have to implement a mandatory operation pointer:

	int (*check_consistency)(struct fscache_object *object)

that corresponds to the above API call.  FS-Cache takes care of pinning the
object and the cookie in memory and managing this call with respect to the
object state.

Original-author: Hongyi Jia <jiayisuse@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Hongyi Jia <jiayisuse@gmail.com>
cc: Milosz Tanski <milosz@adfin.com>

3 files changed, 108 insertions, 24 deletions

diff --git a/fs/fscache/cookie.c b/fs/fscache/cookie.c
index 0e91a3c9fdb2..318e8433527c 100644
--- a/fs/fscache/cookie.c
+++ b/fs/fscache/cookie.c
@@ -558,3 +558,74 @@ void __fscache_cookie_put(struct fscache_cookie *cookie)
 
         _leave("");
 }
+
+/*
+ * check the consistency between the netfs inode and the backing cache
+ *
+ * NOTE: it only serves no-index type
+ */
+int __fscache_check_consistency(struct fscache_cookie *cookie)
+{
+        struct fscache_operation *op;
+        struct fscache_object *object;
+        int ret;
+
+        _enter("%p,", cookie);
+
+        ASSERTCMP(cookie->def->type, ==, FSCACHE_COOKIE_TYPE_DATAFILE);
+
+        if (fscache_wait_for_deferred_lookup(cookie) < 0)
+                return -ERESTARTSYS;
+
+        if (hlist_empty(&cookie->backing_objects))
+                return 0;
+
+        op = kzalloc(sizeof(*op), GFP_NOIO | __GFP_NOMEMALLOC | __GFP_NORETRY);
+        if (!op)
+                return -ENOMEM;
+
+        fscache_operation_init(op, NULL, NULL);
+        op->flags = FSCACHE_OP_MYTHREAD |
+                (1 << FSCACHE_OP_WAITING);
+
+        spin_lock(&cookie->lock);
+
+        if (hlist_empty(&cookie->backing_objects))
+                goto inconsistent;
+        object = hlist_entry(cookie->backing_objects.first,
+                             struct fscache_object, cookie_link);
+        if (test_bit(FSCACHE_IOERROR, &object->cache->flags))
+                goto inconsistent;
+
+        op->debug_id = atomic_inc_return(&fscache_op_debug_id);
+
+        atomic_inc(&cookie->n_active);
+        if (fscache_submit_op(object, op) < 0)
+                goto submit_failed;
+
+        /* the work queue now carries its own ref on the object */
+        spin_unlock(&cookie->lock);
+
+        ret = fscache_wait_for_operation_activation(object, op,
+                                                    NULL, NULL, NULL);
+        if (ret == 0) {
+                /* ask the cache to honour the operation */
+                ret = object->cache->ops->check_consistency(op);
+                fscache_op_complete(op, false);
+        } else if (ret == -ENOBUFS) {
+                ret = 0;
+        }
+
+        fscache_put_operation(op);
+        _leave(" = %d", ret);
+        return ret;
+
+submit_failed:
+        atomic_dec(&cookie->n_active);
+inconsistent:
+        spin_unlock(&cookie->lock);
+        kfree(op);
+        _leave(" = -ESTALE");
+        return -ESTALE;
+}
+EXPORT_SYMBOL(__fscache_check_consistency);
diff --git a/fs/fscache/internal.h b/fs/fscache/internal.h
index 12d505bedb5c..4226f6680b06 100644
--- a/fs/fscache/internal.h
+++ b/fs/fscache/internal.h
@@ -130,6 +130,12 @@ extern void fscache_operation_gc(struct work_struct *);
 /*
  * page.c
  */
+extern int fscache_wait_for_deferred_lookup(struct fscache_cookie *);
+extern int fscache_wait_for_operation_activation(struct fscache_object *,
+                                                 struct fscache_operation *,
+                                                 atomic_t *,
+                                                 atomic_t *,
+                                                 void (*)(struct fscache_operation *));
 extern void fscache_invalidate_writes(struct fscache_cookie *);
 
 /*
diff --git a/fs/fscache/page.c b/fs/fscache/page.c
index d479ab3c63e4..793e3d5ca4b5 100644
--- a/fs/fscache/page.c
+++ b/fs/fscache/page.c
@@ -278,7 +278,7 @@ static struct fscache_retrieval *fscache_alloc_retrieval(
 /*
  * wait for a deferred lookup to complete
  */
-static int fscache_wait_for_deferred_lookup(struct fscache_cookie *cookie)
+int fscache_wait_for_deferred_lookup(struct fscache_cookie *cookie)
 {
         unsigned long jif;
 
@@ -322,42 +322,46 @@ static void fscache_do_cancel_retrieval(struct fscache_operation *_op)
 /*
  * wait for an object to become active (or dead)
  */
-static int fscache_wait_for_retrieval_activation(struct fscache_object *object,
-                                                 struct fscache_retrieval *op,
-                                                 atomic_t *stat_op_waits,
-                                                 atomic_t *stat_object_dead)
+int fscache_wait_for_operation_activation(struct fscache_object *object,
+                                          struct fscache_operation *op,
+                                          atomic_t *stat_op_waits,
+                                          atomic_t *stat_object_dead,
+                                          void (*do_cancel)(struct fscache_operation *))
 {
         int ret;
 
-        if (!test_bit(FSCACHE_OP_WAITING, &op->op.flags))
+        if (!test_bit(FSCACHE_OP_WAITING, &op->flags))
                 goto check_if_dead;
 
         _debug(">>> WT");
-        fscache_stat(stat_op_waits);
-        if (wait_on_bit(&op->op.flags, FSCACHE_OP_WAITING,
+        if (stat_op_waits)
+                fscache_stat(stat_op_waits);
+        if (wait_on_bit(&op->flags, FSCACHE_OP_WAITING,
                         fscache_wait_bit_interruptible,
                         TASK_INTERRUPTIBLE) != 0) {
-                ret = fscache_cancel_op(&op->op, fscache_do_cancel_retrieval);
+                ret = fscache_cancel_op(op, do_cancel);
                 if (ret == 0)
                         return -ERESTARTSYS;
 
                 /* it's been removed from the pending queue by another party,
                  * so we should get to run shortly */
-                wait_on_bit(&op->op.flags, FSCACHE_OP_WAITING,
+                wait_on_bit(&op->flags, FSCACHE_OP_WAITING,
                             fscache_wait_bit, TASK_UNINTERRUPTIBLE);
         }
         _debug("<<< GO");
 
 check_if_dead:
-        if (op->op.state == FSCACHE_OP_ST_CANCELLED) {
-                fscache_stat(stat_object_dead);
+        if (op->state == FSCACHE_OP_ST_CANCELLED) {
+                if (stat_object_dead)
+                        fscache_stat(stat_object_dead);
                 _leave(" = -ENOBUFS [cancelled]");
                 return -ENOBUFS;
         }
         if (unlikely(fscache_object_is_dead(object))) {
-                pr_err("%s() = -ENOBUFS [obj dead %d]\n", __func__, op->op.state);
-                fscache_cancel_op(&op->op, fscache_do_cancel_retrieval);
-                fscache_stat(stat_object_dead);
+                pr_err("%s() = -ENOBUFS [obj dead %d]\n", __func__, op->state);
+                fscache_cancel_op(op, do_cancel);
+                if (stat_object_dead)
+                        fscache_stat(stat_object_dead);
                 return -ENOBUFS;
         }
         return 0;
@@ -432,10 +436,11 @@ int __fscache_read_or_alloc_page(struct fscache_cookie *cookie,
 
         /* we wait for the operation to become active, and then process it
          * *here*, in this thread, and not in the thread pool */
-        ret = fscache_wait_for_retrieval_activation(
-                object, op,
+        ret = fscache_wait_for_operation_activation(
+                object, &op->op,
                 __fscache_stat(&fscache_n_retrieval_op_waits),
-                __fscache_stat(&fscache_n_retrievals_object_dead));
+                __fscache_stat(&fscache_n_retrievals_object_dead),
+                fscache_do_cancel_retrieval);
         if (ret < 0)
                 goto error;
 
@@ -557,10 +562,11 @@ int __fscache_read_or_alloc_pages(struct fscache_cookie *cookie,
 
         /* we wait for the operation to become active, and then process it
          * *here*, in this thread, and not in the thread pool */
-        ret = fscache_wait_for_retrieval_activation(
-                object, op,
+        ret = fscache_wait_for_operation_activation(
+                object, &op->op,
                 __fscache_stat(&fscache_n_retrieval_op_waits),
-                __fscache_stat(&fscache_n_retrievals_object_dead));
+                __fscache_stat(&fscache_n_retrievals_object_dead),
+                fscache_do_cancel_retrieval);
         if (ret < 0)
                 goto error;
 
@@ -658,10 +664,11 @@ int __fscache_alloc_page(struct fscache_cookie *cookie,
 
         fscache_stat(&fscache_n_alloc_ops);
 
-        ret = fscache_wait_for_retrieval_activation(
-                object, op,
+        ret = fscache_wait_for_operation_activation(
+                object, &op->op,
                 __fscache_stat(&fscache_n_alloc_op_waits),
-                __fscache_stat(&fscache_n_allocs_object_dead));
+                __fscache_stat(&fscache_n_allocs_object_dead),
+                fscache_do_cancel_retrieval);
         if (ret < 0)
                 goto error;