fuse: implement NFS-like readdirplus support

This patch implements readdirplus support in FUSE, similar to NFS.
The payload returned in the readdirplus call contains
'fuse_entry_out' structure thereby providing all the necessary inputs
for 'faking' a lookup() operation on the spot.

If the dentry and inode already existed (for e.g. in a re-run of ls -l)
then just the inode attributes timeout and dentry timeout are refreshed.

With a simple client->network->server implementation of a FUSE based
filesystem, the following performance observations were made:

Test: Performing a filesystem crawl over 20,000 files with

sh# time ls -lR /mnt

Without readdirplus:
Run 1: 18.1s
Run 2: 16.0s
Run 3: 16.2s

With readdirplus:
Run 1: 4.1s
Run 2: 3.8s
Run 3: 3.8s

The performance improvement is significant as it avoided 20,000 upcalls
calls (lookup). Cache consistency is no worse than what already is.

Signed-off-by: Anand V. Avati <avati@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

1 files changed, 12 insertions, 0 deletions

diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index d8c713e148e3..5dc1fea49ecd 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -193,6 +193,7 @@ struct fuse_file_lock {
 #define FUSE_FLOCK_LOCKS        (1 << 10)
 #define FUSE_HAS_IOCTL_DIR      (1 << 11)
 #define FUSE_AUTO_INVAL_DATA    (1 << 12)
+#define FUSE_DO_READDIRPLUS     (1 << 13)
 
 /**
  * CUSE INIT request/reply flags
@@ -299,6 +300,7 @@ enum fuse_opcode {
         FUSE_NOTIFY_REPLY  = 41,
         FUSE_BATCH_FORGET  = 42,
         FUSE_FALLOCATE     = 43,
+        FUSE_READDIRPLUS   = 44,
 
         /* CUSE specific operations */
         CUSE_INIT          = 4096,
@@ -630,6 +632,16 @@ struct fuse_dirent {
 #define FUSE_DIRENT_SIZE(d) \
         FUSE_DIRENT_ALIGN(FUSE_NAME_OFFSET + (d)->namelen)
 
+struct fuse_direntplus {
+        struct fuse_entry_out entry_out;
+        struct fuse_dirent dirent;
+};
+
+#define FUSE_NAME_OFFSET_DIRENTPLUS \
+        offsetof(struct fuse_direntplus, dirent.name)
+#define FUSE_DIRENTPLUS_SIZE(d) \
+        FUSE_DIRENT_ALIGN(FUSE_NAME_OFFSET_DIRENTPLUS + (d)->dirent.namelen)
+
 struct fuse_notify_inval_inode_out {
         __u64   ino;
         __s64   off;