fuse: allow control of adaptive readdirplus use

For some filesystems (e.g. GlusterFS), the cost of performing a
normal readdir and readdirplus are identical.  Since adaptively
using readdirplus has no benefit for those systems, give
users/filesystems the option to control adaptive readdirplus use.

v2 of this patch incorporates Miklos's suggestion to simplify the code,
as well as improving consistency of macro names and documentation.
Signed-off-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

fs/fuse/dir.c

@@ -21,6 +21,8 @@ static bool fuse_use_readdirplus(struct inode *dir, struct file *filp)
 
 	if (!fc->do_readdirplus)
 		return false;
+	if (!fc->readdirplus_auto)
+		return true;
 	if (test_and_clear_bit(FUSE_I_ADVISE_RDPLUS, &fi->state))
 		return true;
 	if (filp->f_pos == 0)

fs/fuse/fuse_i.h

@@ -514,9 +514,12 @@ struct fuse_conn {
 	/** Use enhanced/automatic page cache invalidation. */
 	unsigned auto_inval_data:1;
 
-	/** Does the filesystem support readdir-plus? */
+	/** Does the filesystem support readdirplus? */
 	unsigned do_readdirplus:1;
 
+	/** Does the filesystem want adaptive readdirplus? */
+	unsigned readdirplus_auto:1;
+
 	/** The number of requests waiting for completion */
 	atomic_t num_waiting;
 

fs/fuse/inode.c

@@ -866,6 +866,8 @@ static void process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
 				fc->auto_inval_data = 1;
 			if (arg->flags & FUSE_DO_READDIRPLUS)
 				fc->do_readdirplus = 1;
+			if (arg->flags & FUSE_READDIRPLUS_AUTO)
+				fc->readdirplus_auto = 1;
 		} else {
 			ra_pages = fc->max_read / PAGE_CACHE_SIZE;
 			fc->no_lock = 1;
@@ -893,7 +895,7 @@ static void fuse_send_init(struct fuse_conn *fc, struct fuse_req *req)
 		FUSE_EXPORT_SUPPORT | FUSE_BIG_WRITES | FUSE_DONT_MASK |
 		FUSE_SPLICE_WRITE | FUSE_SPLICE_MOVE | FUSE_SPLICE_READ |
 		FUSE_FLOCK_LOCKS | FUSE_IOCTL_DIR | FUSE_AUTO_INVAL_DATA |
-		FUSE_DO_READDIRPLUS;
+		FUSE_DO_READDIRPLUS | FUSE_READDIRPLUS_AUTO;
 	req->in.h.opcode = FUSE_INIT;
 	req->in.numargs = 1;
 	req->in.args[0].size = sizeof(*arg);

include/uapi/linux/fuse.h

@@ -218,6 +218,8 @@ struct fuse_file_lock {
  * FUSE_FLOCK_LOCKS: remote locking for BSD style file locks
  * FUSE_HAS_IOCTL_DIR: kernel supports ioctl on directories
  * FUSE_AUTO_INVAL_DATA: automatically invalidate cached pages
+ * FUSE_DO_READDIRPLUS: do READDIRPLUS (READDIR+LOOKUP in one)
+ * FUSE_READDIRPLUS_AUTO: adaptive readdirplus
  */
 #define FUSE_ASYNC_READ		(1 << 0)
 #define FUSE_POSIX_LOCKS	(1 << 1)
@@ -233,6 +235,7 @@ struct fuse_file_lock {
 #define FUSE_HAS_IOCTL_DIR	(1 << 11)
 #define FUSE_AUTO_INVAL_DATA	(1 << 12)
 #define FUSE_DO_READDIRPLUS	(1 << 13)
+#define FUSE_READDIRPLUS_AUTO	(1 << 14)
 
 /**
  * CUSE INIT request/reply flags