fuse: Turn writeback cache on

Introduce a bit kernel and userspace exchange between each-other on
the init stage and turn writeback on if the userspace want this and
mount option 'allow_wbcache' is present (controlled by fusermount).

Also add each writable file into per-inode write list and call the
generic_file_aio_write to make use of the Linux page cache engine.

Signed-off-by: Maxim Patlasov <MPatlasov@parallels.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

3 files changed, 21 insertions, 2 deletions

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 276433021561..d03a35d3197e 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -224,6 +224,8 @@ void fuse_finish_open(struct inode *inode, struct file *file)
                 spin_unlock(&fc->lock);
                 fuse_invalidate_attr(inode);
         }
+        if ((file->f_mode & FMODE_WRITE) && fc->writeback_cache)
+                fuse_link_write_file(file);
 }
 
 int fuse_open_common(struct inode *inode, struct file *file, bool isdir)
@@ -1197,6 +1199,15 @@ static ssize_t fuse_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
         struct iov_iter i;
         loff_t endbyte = 0;
 
+        if (get_fuse_conn(inode)->writeback_cache) {
+                /* Update size (EOF optimization) and mode (SUID clearing) */
+                err = fuse_update_attributes(mapping->host, NULL, file, NULL);
+                if (err)
+                        return err;
+
+                return generic_file_aio_write(iocb, iov, nr_segs, pos);
+        }
+
         WARN_ON(iocb->ki_pos != pos);
 
         ocount = 0;
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 1061b0d9b86d..9ba191917415 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -887,6 +887,8 @@ static void process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
                         }
                         if (arg->flags & FUSE_ASYNC_DIO)
                                 fc->async_dio = 1;
+                        if (arg->flags & FUSE_WRITEBACK_CACHE)
+                                fc->writeback_cache = 1;
                 } else {
                         ra_pages = fc->max_read / PAGE_CACHE_SIZE;
                         fc->no_lock = 1;
@@ -914,7 +916,8 @@ 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_READDIRPLUS_AUTO | FUSE_ASYNC_DIO;
+                FUSE_DO_READDIRPLUS | FUSE_READDIRPLUS_AUTO | FUSE_ASYNC_DIO |
+                FUSE_WRITEBACK_CACHE;
         req->in.h.opcode = FUSE_INIT;
         req->in.numargs = 1;
         req->in.args[0].size = sizeof(*arg);
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index 60bb2f9f7b74..cf4750e1bb49 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -93,6 +93,9 @@
  *
  * 7.22
  *  - add FUSE_ASYNC_DIO
+ *
+ * 7.23
+ *  - add FUSE_WRITEBACK_CACHE
  */
 
 #ifndef _LINUX_FUSE_H
@@ -128,7 +131,7 @@
 #define FUSE_KERNEL_VERSION 7
 
 /** Minor version number of this interface */
-#define FUSE_KERNEL_MINOR_VERSION 22
+#define FUSE_KERNEL_MINOR_VERSION 23
 
 /** The node ID of the root inode */
 #define FUSE_ROOT_ID 1
@@ -219,6 +222,7 @@ struct fuse_file_lock {
  * FUSE_DO_READDIRPLUS: do READDIRPLUS (READDIR+LOOKUP in one)
  * FUSE_READDIRPLUS_AUTO: adaptive readdirplus
  * FUSE_ASYNC_DIO: asynchronous direct I/O submission
+ * FUSE_WRITEBACK_CACHE: use writeback cache for buffered writes
  */
 #define FUSE_ASYNC_READ         (1 << 0)
 #define FUSE_POSIX_LOCKS        (1 << 1)
@@ -236,6 +240,7 @@ struct fuse_file_lock {
 #define FUSE_DO_READDIRPLUS     (1 << 13)
 #define FUSE_READDIRPLUS_AUTO   (1 << 14)
 #define FUSE_ASYNC_DIO          (1 << 15)
+#define FUSE_WRITEBACK_CACHE    (1 << 16)
 
 /**
  * CUSE INIT request/reply flags