netfs, cachefiles: Pass upper bound length to allow expansion

Make netfslib pass the maximum length to the ->prepare_write() op to tell
the cache how much it can expand the length of a write to.  This allows a
write to the server at the end of a file to be limited to a few bytes
whilst writing an entire block to the cache (something required by direct
I/O).

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org

fs/cachefiles/internal.h

@@ -233,7 +233,7 @@ extern bool cachefiles_begin_operation(struct netfs_cache_resources *cres,
 				       enum fscache_want_state want_state);
 extern int __cachefiles_prepare_write(struct cachefiles_object *object,
 				      struct file *file,
-				      loff_t *_start, size_t *_len,
+				      loff_t *_start, size_t *_len, size_t upper_len,
 				      bool no_space_allocated_yet);
 extern int __cachefiles_write(struct cachefiles_object *object,
 			      struct file *file,

fs/cachefiles/io.c

@@ -518,7 +518,7 @@ cachefiles_prepare_ondemand_read(struct netfs_cache_resources *cres,
  */
 int __cachefiles_prepare_write(struct cachefiles_object *object,
 			       struct file *file,
-			       loff_t *_start, size_t *_len,
+			       loff_t *_start, size_t *_len, size_t upper_len,
 			       bool no_space_allocated_yet)
 {
 	struct cachefiles_cache *cache = object->volume->cache;
@@ -530,6 +530,8 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,
 	down = start - round_down(start, PAGE_SIZE);
 	*_start = start - down;
 	*_len = round_up(down + len, PAGE_SIZE);
+	if (down < start || *_len > upper_len)
+		return -ENOBUFS;
 
 	/* We need to work out whether there's sufficient disk space to perform
 	 * the write - but we can skip that check if we have space already
@@ -592,8 +594,8 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,
 }
 
 static int cachefiles_prepare_write(struct netfs_cache_resources *cres,
-				    loff_t *_start, size_t *_len, loff_t i_size,
-				    bool no_space_allocated_yet)
+				    loff_t *_start, size_t *_len, size_t upper_len,
+				    loff_t i_size, bool no_space_allocated_yet)
 {
 	struct cachefiles_object *object = cachefiles_cres_object(cres);
 	struct cachefiles_cache *cache = object->volume->cache;
@@ -609,7 +611,7 @@ static int cachefiles_prepare_write(struct netfs_cache_resources *cres,
 
 	cachefiles_begin_secure(cache, &saved_cred);
 	ret = __cachefiles_prepare_write(object, cachefiles_cres_file(cres),
-					 _start, _len,
+					 _start, _len, upper_len,
 					 no_space_allocated_yet);
 	cachefiles_end_secure(cache, saved_cred);
 	return ret;

fs/cachefiles/ondemand.c

@@ -52,7 +52,7 @@ static ssize_t cachefiles_ondemand_fd_write_iter(struct kiocb *kiocb,
 		return -ENOBUFS;
 
 	cachefiles_begin_secure(cache, &saved_cred);
-	ret = __cachefiles_prepare_write(object, file, &pos, &len, true);
+	ret = __cachefiles_prepare_write(object, file, &pos, &len, len, true);
 	cachefiles_end_secure(cache, saved_cred);
 	if (ret < 0)
 		return ret;

fs/netfs/fscache_io.c

@@ -237,7 +237,7 @@ void __fscache_write_to_cache(struct fscache_cookie *cookie,
 				    fscache_access_io_write) < 0)
 		goto abandon_free;
 
-	ret = cres->ops->prepare_write(cres, &start, &len, i_size, false);
+	ret = cres->ops->prepare_write(cres, &start, &len, len, i_size, false);
 	if (ret < 0)
 		goto abandon_end;
 

fs/netfs/io.c

@@ -199,7 +199,7 @@ static void netfs_rreq_do_write_to_cache(struct netfs_io_request *rreq)
 		}
 
 		ret = cres->ops->prepare_write(cres, &subreq->start, &subreq->len,
-					       rreq->i_size, true);
+					       subreq->len, rreq->i_size, true);
 		if (ret < 0) {
 			trace_netfs_failure(rreq, subreq, ret, netfs_fail_prepare_write);
 			trace_netfs_sreq(subreq, netfs_sreq_trace_write_skip);

fs/netfs/objects.c

@@ -33,6 +33,7 @@ struct netfs_io_request *netfs_alloc_request(struct address_space *mapping,
 
 	rreq->start	= start;
 	rreq->len	= len;
+	rreq->upper_len	= len;
 	rreq->origin	= origin;
 	rreq->netfs_ops	= ctx->ops;
 	rreq->mapping	= mapping;

fs/netfs/output.c

@@ -280,7 +280,7 @@ EXPORT_SYMBOL(netfs_queue_write_request);
  */
 static void netfs_set_up_write_to_cache(struct netfs_io_request *wreq)
 {
-	struct netfs_cache_resources *cres;
+	struct netfs_cache_resources *cres = &wreq->cache_resources;
 	struct netfs_io_subrequest *subreq;
 	struct netfs_inode *ctx = netfs_inode(wreq->inode);
 	struct fscache_cookie *cookie = netfs_i_cookie(ctx);
@@ -294,26 +294,21 @@ static void netfs_set_up_write_to_cache(struct netfs_io_request *wreq)
 	}
 
 	_debug("write to cache");
-	subreq = netfs_create_write_request(wreq, NETFS_WRITE_TO_CACHE, start, len,
-					    netfs_write_to_cache_op_worker);
-	if (!subreq)
+	ret = fscache_begin_write_operation(cres, cookie);
+	if (ret < 0)
 		return;
 
-	cres = &wreq->cache_resources;
-	ret = fscache_begin_read_operation(cres, cookie);
-	if (ret < 0) {
-		netfs_write_subrequest_terminated(subreq, ret, false);
+	ret = cres->ops->prepare_write(cres, &start, &len, wreq->upper_len,
+				       i_size_read(wreq->inode), true);
+	if (ret < 0)
 		return;
-	}
 
-	ret = cres->ops->prepare_write(cres, &start, &len, i_size_read(wreq->inode),
-				       true);
-	if (ret < 0) {
-		netfs_write_subrequest_terminated(subreq, ret, false);
+	subreq = netfs_create_write_request(wreq, NETFS_WRITE_TO_CACHE, start, len,
+					    netfs_write_to_cache_op_worker);
+	if (!subreq)
 		return;
-	}
 
-	netfs_queue_write_request(subreq);
+	netfs_write_to_cache_op(subreq);
 }
 
 /*

fs/smb/client/fscache.c

@@ -180,7 +180,7 @@ static int fscache_fallback_write_pages(struct inode *inode, loff_t start, size_
 	if (ret < 0)
 		return ret;
 
-	ret = cres.ops->prepare_write(&cres, &start, &len, i_size_read(inode),
+	ret = cres.ops->prepare_write(&cres, &start, &len, len, i_size_read(inode),
 				      no_space_allocated_yet);
 	if (ret == 0)
 		ret = fscache_write(&cres, start, &iter, NULL, NULL);

include/linux/netfs.h

@@ -261,6 +261,7 @@ struct netfs_io_request {
 	atomic_t		nr_copy_ops;	/* Number of copy-to-cache ops in progress */
 	size_t			submitted;	/* Amount submitted for I/O so far */
 	size_t			len;		/* Length of the request */
+	size_t			upper_len;	/* Length can be extended to here */
 	size_t			transferred;	/* Amount to be indicated as transferred */
 	short			error;		/* 0 or error that occurred */
 	enum netfs_io_origin	origin;		/* Origin of the request */
@@ -357,8 +358,8 @@ struct netfs_cache_ops {
 	 * actually do.
 	 */
 	int (*prepare_write)(struct netfs_cache_resources *cres,
-			     loff_t *_start, size_t *_len, loff_t i_size,
-			     bool no_space_allocated_yet);
+			     loff_t *_start, size_t *_len, size_t upper_len,
+			     loff_t i_size, bool no_space_allocated_yet);
 
 	/* Prepare an on-demand read operation, shortening it to a cached/uncached
 	 * boundary as appropriate.