fuse: Increase FUSE_NAME_MAX to PATH_MAX

Our file system has a translation capability for S3-to-posix.
The current value of 1kiB is enough to cover S3 keys, but
does not allow encoding of %xx escape characters.
The limit is increased to (PATH_MAX - 1), as we need
3 x 1024 and that is close to PATH_MAX (4kB) already.
-1 is used as the terminating null is not included in the
length calculation.

Testing large file names was hard with libfuse/example file systems,
so I created a new memfs that does not have a 255 file name length
limitation.
libfuse/libfuse#1077

The connection is initialized with FUSE_NAME_LOW_MAX, which
is set to the previous value of FUSE_NAME_MAX of 1024. With
FUSE_MIN_READ_BUFFER of 8192 that is enough for two file names
+ fuse headers.
When FUSE_INIT reply sets max_pages to a value > 1 we know
that fuse daemon supports request buffers of at least 2 pages
(+ header) and can therefore hold 2 x PATH_MAX file names - operations
like rename or link that need two file names are no issue then.

Signed-off-by: Bernd Schubert <bschubert@ddn.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

Author: bsbernd

fs/fuse/dev.c

@@ -1657,7 +1657,7 @@ static int fuse_notify_inval_entry(struct fuse_conn *fc, unsigned int size,
 		goto err;
 
 	err = -ENAMETOOLONG;
-	if (outarg.namelen > FUSE_NAME_MAX)
+	if (outarg.namelen > fc->name_max)
 		goto err;
 
 	err = -EINVAL;
@@ -1706,7 +1706,7 @@ static int fuse_notify_delete(struct fuse_conn *fc, unsigned int size,
 		goto err;
 
 	err = -ENAMETOOLONG;
-	if (outarg.namelen > FUSE_NAME_MAX)
+	if (outarg.namelen > fc->name_max)
 		goto err;
 
 	err = -EINVAL;

fs/fuse/dir.c

@@ -370,7 +370,7 @@ int fuse_lookup_name(struct super_block *sb, u64 nodeid, const struct qstr *name
 
 	*inode = NULL;
 	err = -ENAMETOOLONG;
-	if (name->len > FUSE_NAME_MAX)
+	if (name->len > fm->fc->name_max)
 		goto out;
 
 

fs/fuse/fuse_i.h

@@ -38,8 +38,12 @@
 /** Bias for fi->writectr, meaning new writepages must not be sent */
 #define FUSE_NOWRITE INT_MIN
 
-/** It could be as large as PATH_MAX, but would that have any uses? */
-#define FUSE_NAME_MAX 1024
+/** Maximum length of a filename, not including terminating null */
+
+/* maximum, small enough for FUSE_MIN_READ_BUFFER*/
+#define FUSE_NAME_LOW_MAX 1024
+/* maximum, but needs a request buffer > FUSE_MIN_READ_BUFFER */
+#define FUSE_NAME_MAX (PATH_MAX - 1)
 
 /** Number of dentries for each connection in the control filesystem */
 #define FUSE_CTL_NUM_DENTRIES 5
@@ -924,6 +928,9 @@ struct fuse_conn {
 	/** Version counter for evict inode */
 	atomic64_t evict_ctr;
 
+	/* maximum file name length */
+	u32 name_max;
+
 	/** Called on final put */
 	void (*release)(struct fuse_conn *);
 

fs/fuse/inode.c

@@ -982,6 +982,7 @@ void fuse_conn_init(struct fuse_conn *fc, struct fuse_mount *fm,
 	fc->user_ns = get_user_ns(user_ns);
 	fc->max_pages = FUSE_DEFAULT_MAX_PAGES_PER_REQ;
 	fc->max_pages_limit = fuse_max_pages_limit;
+	fc->name_max = FUSE_NAME_LOW_MAX;
 	fc->timeout.req_timeout = 0;
 
 	if (IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
@@ -1373,6 +1374,13 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args,
 				fc->max_pages =
 					min_t(unsigned int, fc->max_pages_limit,
 					max_t(unsigned int, arg->max_pages, 1));
+
+				/*
+				 * PATH_MAX file names might need two pages for
+				 * ops like rename
+				 */
+				if (fc->max_pages > 1)
+					fc->name_max = FUSE_NAME_MAX;
 			}
 			if (IS_ENABLED(CONFIG_FUSE_DAX)) {
 				if (flags & FUSE_MAP_ALIGNMENT &&