[PATCH 46/67] fscache: Provide resize operation

[David Howells <dhowells@redhat.com>]

Provide a cache operation to resize an object.  This is intended to be run
synchronously rather than being deferred as it really needs to run inside
the inode lock on the netfs inode from ->setattr() to correctly order with
respect to other truncates and writes.

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

 fs/cachefiles/interface.c      |   93 ++++++++++++++++++++++++----------------
 fs/fscache/io.c                |   25 +++++++++++
 fs/fscache/stats.c             |    6 ++-
 include/linux/fscache-cache.h  |    4 ++
 include/linux/fscache.h        |   18 ++++++++
 include/trace/events/fscache.h |   23 ++++++++++
 6 files changed, 130 insertions(+), 39 deletions(-)

diff --git a/fs/cachefiles/interface.c b/fs/cachefiles/interface.c
index 38ae34b7aaf4..f90f6ddd07a5 100644
--- a/fs/cachefiles/interface.c
+++ b/fs/cachefiles/interface.c
@@ -9,6 +9,7 @@
 #include <linux/mount.h>
 #include <linux/xattr.h>
 #include <linux/file.h>
+#include <linux/falloc.h>
 #include <trace/events/fscache.h>
 #include "internal.h"
 
@@ -134,55 +135,72 @@ struct cachefiles_object *cachefiles_grab_object(struct cachefiles_object *objec
 }
 
 /*
- * update the auxiliary data for an object object on disk
+ * Shorten the backing object to discard any dirty data and free up
+ * any unused granules.
  */
-static void cachefiles_update_object(struct cachefiles_object *object)
+static bool cachefiles_shorten_object(struct cachefiles_object *object,
+				      struct file *file, loff_t new_size)
 {
 	struct cachefiles_cache *cache = object->volume->cache;
-	const struct cred *saved_cred;
-	struct file *file = object->file;
-	loff_t object_size, i_size;
+	struct inode *inode = file_inode(file);
+	loff_t i_size, dio_size;
 	int ret;
 
-	_enter("{OBJ%x}", object->debug_id);
+	dio_size = round_up(new_size, CACHEFILES_DIO_BLOCK_SIZE);
+	i_size = i_size_read(inode);
 
-	cachefiles_begin_secure(cache, &saved_cred);
+	trace_cachefiles_trunc(object, inode, i_size, dio_size,
+			       cachefiles_trunc_shrink);
+	ret = vfs_truncate(&file->f_path, dio_size);
+	if (ret < 0) {
+		cachefiles_io_error_obj(object, "Trunc-to-size failed %d", ret);
+		cachefiles_remove_object_xattr(cache, file->f_path.dentry);
+		return false;
+	}
 
-	object_size = object->cookie->object_size;
-	i_size = i_size_read(file_inode(file));
-	if (i_size > object_size) {
-		_debug("trunc %llx -> %llx", i_size, object_size);
-		trace_cachefiles_trunc(object, file_inode(file),
-				       i_size, object_size,
-				       cachefiles_trunc_shrink);
-		ret = vfs_truncate(&file->f_path, object_size);
+	if (new_size < dio_size) {
+		trace_cachefiles_trunc(object, inode, dio_size, new_size,
+				       cachefiles_trunc_dio_adjust);
+		ret = vfs_fallocate(file, FALLOC_FL_ZERO_RANGE,
+				    new_size, dio_size);
 		if (ret < 0) {
-			cachefiles_io_error_obj(object, "Trunc-to-size failed");
+			cachefiles_io_error_obj(object, "Trunc-to-dio-size failed %d", ret);
 			cachefiles_remove_object_xattr(cache, file->f_path.dentry);
-			goto out;
-		}
-
-		object_size = round_up(object_size, CACHEFILES_DIO_BLOCK_SIZE);
-		i_size = i_size_read(file_inode(file));
-		_debug("trunc %llx -> %llx", i_size, object_size);
-		if (i_size < object_size) {
-			trace_cachefiles_trunc(object, file_inode(file),
-					       i_size, object_size,
-					       cachefiles_trunc_dio_adjust);
-			ret = vfs_truncate(&file->f_path, object_size);
-			if (ret < 0) {
-				cachefiles_io_error_obj(object, "Trunc-to-dio-size failed");
-				cachefiles_remove_object_xattr(cache, file->f_path.dentry);
-				goto out;
-			}
+			return false;
 		}
 	}
 
-	cachefiles_set_object_xattr(object);
+	return true;
+}
 
-out:
-	cachefiles_end_secure(cache, saved_cred);
-	_leave("");
+/*
+ * Resize the backing object.
+ */
+static void cachefiles_resize_cookie(struct netfs_cache_resources *cres,
+				     loff_t new_size)
+{
+	struct cachefiles_object *object = cachefiles_cres_object(cres);
+	struct cachefiles_cache *cache = object->volume->cache;
+	struct fscache_cookie *cookie = object->cookie;
+	const struct cred *saved_cred;
+	struct file *file = cachefiles_cres_file(cres);
+	loff_t old_size = cookie->object_size;
+
+	_enter("%llu->%llu", old_size, new_size);
+
+	if (new_size < old_size) {
+		cachefiles_begin_secure(cache, &saved_cred);
+		cachefiles_shorten_object(object, file, new_size);
+		cachefiles_end_secure(cache, saved_cred);
+		object->cookie->object_size = new_size;
+		return;
+	}
+
+	/* The file is being expanded.  We don't need to do anything
+	 * particularly.  cookie->initial_size doesn't change and so the point
+	 * at which we have to download before doesn't change.
+	 */
+	cookie->object_size = new_size;
 }
 
 /*
@@ -196,7 +214,7 @@ static void cachefiles_commit_object(struct cachefiles_object *object,
 	if (test_and_clear_bit(FSCACHE_COOKIE_NEEDS_UPDATE, &object->cookie->flags))
 		update = true;
 	if (update)
-		cachefiles_update_object(object);
+		cachefiles_set_object_xattr(object);
 
 	if (test_bit(CACHEFILES_OBJECT_USING_TMPFILE, &object->flags))
 		cachefiles_commit_tmpfile(cache, object);
@@ -440,5 +458,6 @@ const struct fscache_cache_ops cachefiles_cache_ops = {
 	.lookup_cookie		= cachefiles_lookup_cookie,
 	.withdraw_cookie	= cachefiles_withdraw_cookie,
 	.invalidate_cookie	= cachefiles_invalidate_cookie,
+	.resize_cookie		= cachefiles_resize_cookie,
 	.begin_operation	= cachefiles_begin_operation,
 };
diff --git a/fs/fscache/io.c b/fs/fscache/io.c
index ad9798f0c850..8b1a865a0847 100644
--- a/fs/fscache/io.c
+++ b/fs/fscache/io.c
@@ -253,3 +253,28 @@ int fscache_set_page_dirty(struct page *page, struct fscache_cookie *cookie)
 	return 1;
 }
 EXPORT_SYMBOL(fscache_set_page_dirty);
+
+/*
+ * Change the size of a backing object.
+ */
+void __fscache_resize_cookie(struct fscache_cookie *cookie, loff_t new_size)
+{
+	struct netfs_cache_resources cres;
+
+	trace_fscache_resize(cookie, new_size);
+	if (fscache_begin_operation(&cres, cookie, FSCACHE_WANT_WRITE,
+				    fscache_access_io_resize) == 0) {
+		fscache_stat(&fscache_n_resizes);
+		set_bit(FSCACHE_COOKIE_NEEDS_UPDATE, &cookie->flags);
+
+		/* We cannot defer a resize as we need to do it inside the
+		 * netfs's inode lock so that we're serialised with respect to
+		 * writes.
+		 */
+		cookie->volume->cache->ops->resize_cookie(&cres, new_size);
+		fscache_end_operation(&cres);
+	} else {
+		fscache_stat(&fscache_n_resizes_null);
+	}
+}
+EXPORT_SYMBOL(__fscache_resize_cookie);
diff --git a/fs/fscache/stats.c b/fs/fscache/stats.c
index 44b3b901e191..b1174d0dac3e 100644
--- a/fs/fscache/stats.c
+++ b/fs/fscache/stats.c
@@ -97,8 +97,10 @@ int fscache_stats_show(struct seq_file *m, void *v)
 	seq_printf(m, "Invals : n=%u\n",
 		   atomic_read(&fscache_n_invalidates));
 
-	seq_printf(m, "Updates: n=%u\n",
-		   atomic_read(&fscache_n_updates));
+	seq_printf(m, "Updates: n=%u rsz=%u rsn=%u\n",
+		   atomic_read(&fscache_n_updates),
+		   atomic_read(&fscache_n_resizes),
+		   atomic_read(&fscache_n_resizes_null));
 
 	seq_printf(m, "Relinqs: n=%u rtr=%u drop=%u\n",
 		   atomic_read(&fscache_n_relinquishes),
diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
index 22064611d182..2e7265e24df6 100644
--- a/include/linux/fscache-cache.h
+++ b/include/linux/fscache-cache.h
@@ -66,6 +66,10 @@ struct fscache_cache_ops {
 	/* Withdraw an object without any cookie access counts held */
 	void (*withdraw_cookie)(struct fscache_cookie *cookie);
 
+	/* Change the size of a data object */
+	void (*resize_cookie)(struct netfs_cache_resources *cres,
+			      loff_t new_size);
+
 	/* Invalidate an object */
 	bool (*invalidate_cookie)(struct fscache_cookie *cookie);
 
diff --git a/include/linux/fscache.h b/include/linux/fscache.h
index 08663ad7feed..8148193045cd 100644
--- a/include/linux/fscache.h
+++ b/include/linux/fscache.h
@@ -164,6 +164,7 @@ extern struct fscache_cookie *__fscache_acquire_cookie(
 extern void __fscache_use_cookie(struct fscache_cookie *, bool);
 extern void __fscache_unuse_cookie(struct fscache_cookie *, const void *, const loff_t *);
 extern void __fscache_relinquish_cookie(struct fscache_cookie *, bool);
+extern void __fscache_resize_cookie(struct fscache_cookie *, loff_t);
 extern void __fscache_invalidate(struct fscache_cookie *, const void *, loff_t, unsigned int);
 #ifdef FSCACHE_USE_NEW_IO_API
 extern int __fscache_begin_read_operation(struct netfs_cache_resources *, struct fscache_cookie *);
@@ -361,6 +362,23 @@ void fscache_update_cookie(struct fscache_cookie *cookie, const void *aux_data,
 		__fscache_update_cookie(cookie, aux_data, object_size);
 }
 
+/**
+ * fscache_resize_cookie - Request that a cache object be resized
+ * @cookie: The cookie representing the cache object
+ * @new_size: The new size of the object (may be NULL)
+ *
+ * Request that the size of an object be changed.
+ *
+ * See Documentation/filesystems/caching/netfs-api.txt for a complete
+ * description.
+ */
+static inline
+void fscache_resize_cookie(struct fscache_cookie *cookie, loff_t new_size)
+{
+	if (fscache_cookie_enabled(cookie))
+		__fscache_resize_cookie(cookie, new_size);
+}
+
 /**
  * fscache_pin_cookie - Pin a data-storage cache object in its cache
  * @cookie: The cookie representing the cache object
diff --git a/include/trace/events/fscache.h b/include/trace/events/fscache.h
index adde3bb61f0f..9554b43e6fdf 100644
--- a/include/trace/events/fscache.h
+++ b/include/trace/events/fscache.h
@@ -429,6 +429,29 @@ TRACE_EVENT(fscache_invalidate,
 		      __entry->cookie, __entry->new_size)
 	    );
 
+TRACE_EVENT(fscache_resize,
+	    TP_PROTO(struct fscache_cookie *cookie, loff_t new_size),
+
+	    TP_ARGS(cookie, new_size),
+
+	    TP_STRUCT__entry(
+		    __field(unsigned int,		cookie		)
+		    __field(loff_t,			old_size	)
+		    __field(loff_t,			new_size	)
+			     ),
+
+	    TP_fast_assign(
+		    __entry->cookie	= cookie->debug_id;
+		    __entry->old_size	= cookie->object_size;
+		    __entry->new_size	= new_size;
+			   ),
+
+	    TP_printk("c=%08x os=%08llx sz=%08llx",
+		      __entry->cookie,
+		      __entry->old_size,
+		      __entry->new_size)
+	    );
+
 #endif /* _TRACE_FSCACHE_H */
 
 /* This part must be outside protection */