Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse

Pull fuse update from Miklos Szeredi:
 "This series adds cached writeback support to fuse, improving write
  throughput"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse:
  fuse: fix "uninitialized variable" warning
  fuse: Turn writeback cache on
  fuse: Fix O_DIRECT operations vs cached writeback misorder
  fuse: fuse_flush() should wait on writeback
  fuse: Implement write_begin/write_end callbacks
  fuse: restructure fuse_readpage()
  fuse: Flush files on wb close
  fuse: Trust kernel i_mtime only
  fuse: Trust kernel i_size only
  fuse: Connection bit for enabling writeback
  fuse: Prepare to handle short reads
  fuse: Linking file to inode helper

6 files changed, 384 insertions, 84 deletions

diff --git a/fs/fuse/cuse.c b/fs/fuse/cuse.c
index b96a49b37d66..23e363f38302 100644
--- a/fs/fuse/cuse.c
+++ b/fs/fuse/cuse.c
@@ -95,7 +95,7 @@ static ssize_t cuse_read(struct file *file, char __user *buf, size_t count,
         struct iovec iov = { .iov_base = buf, .iov_len = count };
         struct fuse_io_priv io = { .async = 0, .file = file };
 
-        return fuse_direct_io(&io, &iov, 1, count, &pos, 0);
+        return fuse_direct_io(&io, &iov, 1, count, &pos, FUSE_DIO_CUSE);
 }
 
 static ssize_t cuse_write(struct file *file, const char __user *buf,
@@ -109,7 +109,8 @@ static ssize_t cuse_write(struct file *file, const char __user *buf,
          * No locking or generic_write_checks(), the server is
          * responsible for locking and sanity checks.
          */
-        return fuse_direct_io(&io, &iov, 1, count, &pos, 1);
+        return fuse_direct_io(&io, &iov, 1, count, &pos,
+                              FUSE_DIO_WRITE | FUSE_DIO_CUSE);
 }
 
 static int cuse_open(struct inode *inode, struct file *file)
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 1d1292c581c3..5b4e035b364c 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -839,6 +839,14 @@ static void fuse_fillattr(struct inode *inode, struct fuse_attr *attr,
                           struct kstat *stat)
 {
         unsigned int blkbits;
+        struct fuse_conn *fc = get_fuse_conn(inode);
+
+        /* see the comment in fuse_change_attributes() */
+        if (fc->writeback_cache && S_ISREG(inode->i_mode)) {
+                attr->size = i_size_read(inode);
+                attr->mtime = inode->i_mtime.tv_sec;
+                attr->mtimensec = inode->i_mtime.tv_nsec;
+        }
 
         stat->dev = inode->i_sb->s_dev;
         stat->ino = attr->ino;
@@ -1477,12 +1485,16 @@ static long fuse_dir_compat_ioctl(struct file *file, unsigned int cmd,
                                  FUSE_IOCTL_COMPAT | FUSE_IOCTL_DIR);
 }
 
-static bool update_mtime(unsigned ivalid)
+static bool update_mtime(unsigned ivalid, bool trust_local_mtime)
 {
         /* Always update if mtime is explicitly set  */
         if (ivalid & ATTR_MTIME_SET)
                 return true;
 
+        /* Or if kernel i_mtime is the official one */
+        if (trust_local_mtime)
+                return true;
+
         /* If it's an open(O_TRUNC) or an ftruncate(), don't update */
         if ((ivalid & ATTR_SIZE) && (ivalid & (ATTR_OPEN | ATTR_FILE)))
                 return false;
@@ -1491,7 +1503,8 @@ static bool update_mtime(unsigned ivalid)
         return true;
 }
 
-static void iattr_to_fattr(struct iattr *iattr, struct fuse_setattr_in *arg)
+static void iattr_to_fattr(struct iattr *iattr, struct fuse_setattr_in *arg,
+                           bool trust_local_mtime)
 {
         unsigned ivalid = iattr->ia_valid;
 
@@ -1510,11 +1523,11 @@ static void iattr_to_fattr(struct iattr *iattr, struct fuse_setattr_in *arg)
                 if (!(ivalid & ATTR_ATIME_SET))
                         arg->valid |= FATTR_ATIME_NOW;
         }
-        if ((ivalid & ATTR_MTIME) && update_mtime(ivalid)) {
+        if ((ivalid & ATTR_MTIME) && update_mtime(ivalid, trust_local_mtime)) {
                 arg->valid |= FATTR_MTIME;
                 arg->mtime = iattr->ia_mtime.tv_sec;
                 arg->mtimensec = iattr->ia_mtime.tv_nsec;
-                if (!(ivalid & ATTR_MTIME_SET))
+                if (!(ivalid & ATTR_MTIME_SET) && !trust_local_mtime)
                         arg->valid |= FATTR_MTIME_NOW;
         }
 }
@@ -1563,6 +1576,63 @@ void fuse_release_nowrite(struct inode *inode)
         spin_unlock(&fc->lock);
 }
 
+static void fuse_setattr_fill(struct fuse_conn *fc, struct fuse_req *req,
+                              struct inode *inode,
+                              struct fuse_setattr_in *inarg_p,
+                              struct fuse_attr_out *outarg_p)
+{
+        req->in.h.opcode = FUSE_SETATTR;
+        req->in.h.nodeid = get_node_id(inode);
+        req->in.numargs = 1;
+        req->in.args[0].size = sizeof(*inarg_p);
+        req->in.args[0].value = inarg_p;
+        req->out.numargs = 1;
+        if (fc->minor < 9)
+                req->out.args[0].size = FUSE_COMPAT_ATTR_OUT_SIZE;
+        else
+                req->out.args[0].size = sizeof(*outarg_p);
+        req->out.args[0].value = outarg_p;
+}
+
+/*
+ * Flush inode->i_mtime to the server
+ */
+int fuse_flush_mtime(struct file *file, bool nofail)
+{
+        struct inode *inode = file->f_mapping->host;
+        struct fuse_inode *fi = get_fuse_inode(inode);
+        struct fuse_conn *fc = get_fuse_conn(inode);
+        struct fuse_req *req = NULL;
+        struct fuse_setattr_in inarg;
+        struct fuse_attr_out outarg;
+        int err;
+
+        if (nofail) {
+                req = fuse_get_req_nofail_nopages(fc, file);
+        } else {
+                req = fuse_get_req_nopages(fc);
+                if (IS_ERR(req))
+                        return PTR_ERR(req);
+        }
+
+        memset(&inarg, 0, sizeof(inarg));
+        memset(&outarg, 0, sizeof(outarg));
+
+        inarg.valid |= FATTR_MTIME;
+        inarg.mtime = inode->i_mtime.tv_sec;
+        inarg.mtimensec = inode->i_mtime.tv_nsec;
+
+        fuse_setattr_fill(fc, req, inode, &inarg, &outarg);
+        fuse_request_send(fc, req);
+        err = req->out.h.error;
+        fuse_put_request(fc, req);
+
+        if (!err)
+                clear_bit(FUSE_I_MTIME_DIRTY, &fi->state);
+
+        return err;
+}
+
 /*
  * Set attributes, and at the same time refresh them.
  *
@@ -1580,8 +1650,10 @@ int fuse_do_setattr(struct inode *inode, struct iattr *attr,
         struct fuse_setattr_in inarg;
         struct fuse_attr_out outarg;
         bool is_truncate = false;
+        bool is_wb = fc->writeback_cache;
         loff_t oldsize;
         int err;
+        bool trust_local_mtime = is_wb && S_ISREG(inode->i_mode);
 
         if (!(fc->flags & FUSE_DEFAULT_PERMISSIONS))
                 attr->ia_valid |= ATTR_FORCE;
@@ -1610,7 +1682,7 @@ int fuse_do_setattr(struct inode *inode, struct iattr *attr,
 
         memset(&inarg, 0, sizeof(inarg));
         memset(&outarg, 0, sizeof(outarg));
-        iattr_to_fattr(attr, &inarg);
+        iattr_to_fattr(attr, &inarg, trust_local_mtime);
         if (file) {
                 struct fuse_file *ff = file->private_data;
                 inarg.valid |= FATTR_FH;
@@ -1621,17 +1693,7 @@ int fuse_do_setattr(struct inode *inode, struct iattr *attr,
                 inarg.valid |= FATTR_LOCKOWNER;
                 inarg.lock_owner = fuse_lock_owner_id(fc, current->files);
         }
-        req->in.h.opcode = FUSE_SETATTR;
-        req->in.h.nodeid = get_node_id(inode);
-        req->in.numargs = 1;
-        req->in.args[0].size = sizeof(inarg);
-        req->in.args[0].value = &inarg;
-        req->out.numargs = 1;
-        if (fc->minor < 9)
-                req->out.args[0].size = FUSE_COMPAT_ATTR_OUT_SIZE;
-        else
-                req->out.args[0].size = sizeof(outarg);
-        req->out.args[0].value = &outarg;
+        fuse_setattr_fill(fc, req, inode, &inarg, &outarg);
         fuse_request_send(fc, req);
         err = req->out.h.error;
         fuse_put_request(fc, req);
@@ -1648,10 +1710,18 @@ int fuse_do_setattr(struct inode *inode, struct iattr *attr,
         }
 
         spin_lock(&fc->lock);
+        /* the kernel maintains i_mtime locally */
+        if (trust_local_mtime && (attr->ia_valid & ATTR_MTIME)) {
+                inode->i_mtime = attr->ia_mtime;
+                clear_bit(FUSE_I_MTIME_DIRTY, &fi->state);
+        }
+
         fuse_change_attributes_common(inode, &outarg.attr,
                                       attr_timeout(&outarg));
         oldsize = inode->i_size;
-        i_size_write(inode, outarg.attr.size);
+        /* see the comment in fuse_change_attributes() */
+        if (!is_wb || is_truncate || !S_ISREG(inode->i_mode))
+                i_size_write(inode, outarg.attr.size);
 
         if (is_truncate) {
                 /* NOTE: this may release/reacquire fc->lock */
@@ -1663,7 +1733,8 @@ int fuse_do_setattr(struct inode *inode, struct iattr *attr,
          * Only call invalidate_inode_pages2() after removing
          * FUSE_NOWRITE, otherwise fuse_launder_page() would deadlock.
          */
-        if (S_ISREG(inode->i_mode) && oldsize != outarg.attr.size) {
+        if ((is_truncate || !is_wb) &&
+            S_ISREG(inode->i_mode) && oldsize != outarg.attr.size) {
                 truncate_pagecache(inode, outarg.attr.size);
                 invalidate_inode_pages2(inode->i_mapping);
         }
@@ -1875,6 +1946,17 @@ static int fuse_removexattr(struct dentry *entry, const char *name)
         return err;
 }
 
+static int fuse_update_time(struct inode *inode, struct timespec *now,
+                            int flags)
+{
+        if (flags & S_MTIME) {
+                inode->i_mtime = *now;
+                set_bit(FUSE_I_MTIME_DIRTY, &get_fuse_inode(inode)->state);
+                BUG_ON(!S_ISREG(inode->i_mode));
+        }
+        return 0;
+}
+
 static const struct inode_operations fuse_dir_inode_operations = {
         .lookup         = fuse_lookup,
         .mkdir          = fuse_mkdir,
@@ -1914,6 +1996,7 @@ static const struct inode_operations fuse_common_inode_operations = {
         .getxattr       = fuse_getxattr,
         .listxattr      = fuse_listxattr,
         .removexattr    = fuse_removexattr,
+        .update_time    = fuse_update_time,
 };
 
 static const struct inode_operations fuse_symlink_inode_operations = {
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 77bcc303c3ae..65df7d8be4f5 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -188,6 +188,22 @@ int fuse_do_open(struct fuse_conn *fc, u64 nodeid, struct file *file,
 }
 EXPORT_SYMBOL_GPL(fuse_do_open);
 
+static void fuse_link_write_file(struct file *file)
+{
+        struct inode *inode = file_inode(file);
+        struct fuse_conn *fc = get_fuse_conn(inode);
+        struct fuse_inode *fi = get_fuse_inode(inode);
+        struct fuse_file *ff = file->private_data;
+        /*
+         * file may be written through mmap, so chain it onto the
+         * inodes's write_file list
+         */
+        spin_lock(&fc->lock);
+        if (list_empty(&ff->write_entry))
+                list_add(&ff->write_entry, &fi->write_files);
+        spin_unlock(&fc->lock);
+}
+
 void fuse_finish_open(struct inode *inode, struct file *file)
 {
         struct fuse_file *ff = file->private_data;
@@ -208,6 +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)
@@ -292,6 +310,15 @@ static int fuse_open(struct inode *inode, struct file *file)
 
 static int fuse_release(struct inode *inode, struct file *file)
 {
+        struct fuse_conn *fc = get_fuse_conn(inode);
+
+        /* see fuse_vma_close() for !writeback_cache case */
+        if (fc->writeback_cache)
+                filemap_write_and_wait(file->f_mapping);
+
+        if (test_bit(FUSE_I_MTIME_DIRTY, &get_fuse_inode(inode)->state))
+                fuse_flush_mtime(file, true);
+
         fuse_release_common(file, FUSE_RELEASE);
 
         /* return value is ignored by VFS */
@@ -333,12 +360,13 @@ u64 fuse_lock_owner_id(struct fuse_conn *fc, fl_owner_t id)
 }
 
 /*
- * Check if page is under writeback
+ * Check if any page in a range is under writeback
  *
  * This is currently done by walking the list of writepage requests
  * for the inode, which can be pretty inefficient.
  */
-static bool fuse_page_is_writeback(struct inode *inode, pgoff_t index)
+static bool fuse_range_is_writeback(struct inode *inode, pgoff_t idx_from,
+                                   pgoff_t idx_to)
 {
         struct fuse_conn *fc = get_fuse_conn(inode);
         struct fuse_inode *fi = get_fuse_inode(inode);
@@ -351,8 +379,8 @@ static bool fuse_page_is_writeback(struct inode *inode, pgoff_t index)
 
                 BUG_ON(req->inode != inode);
                 curr_index = req->misc.write.in.offset >> PAGE_CACHE_SHIFT;
-                if (curr_index <= index &&
-                    index < curr_index + req->num_pages) {
+                if (idx_from < curr_index + req->num_pages &&
+                    curr_index <= idx_to) {
                         found = true;
                         break;
                 }
@@ -362,6 +390,11 @@ static bool fuse_page_is_writeback(struct inode *inode, pgoff_t index)
         return found;
 }
 
+static inline bool fuse_page_is_writeback(struct inode *inode, pgoff_t index)
+{
+        return fuse_range_is_writeback(inode, index, index);
+}
+
 /*
  * Wait for page writeback to be completed.
  *
@@ -376,6 +409,21 @@ static int fuse_wait_on_page_writeback(struct inode *inode, pgoff_t index)
         return 0;
 }
 
+/*
+ * Wait for all pending writepages on the inode to finish.
+ *
+ * This is currently done by blocking further writes with FUSE_NOWRITE
+ * and waiting for all sent writes to complete.
+ *
+ * This must be called under i_mutex, otherwise the FUSE_NOWRITE usage
+ * could conflict with truncation.
+ */
+static void fuse_sync_writes(struct inode *inode)
+{
+        fuse_set_nowrite(inode);
+        fuse_release_nowrite(inode);
+}
+
 static int fuse_flush(struct file *file, fl_owner_t id)
 {
         struct inode *inode = file_inode(file);
@@ -391,6 +439,14 @@ static int fuse_flush(struct file *file, fl_owner_t id)
         if (fc->no_flush)
                 return 0;
 
+        err = filemap_write_and_wait(file->f_mapping);
+        if (err)
+                return err;
+
+        mutex_lock(&inode->i_mutex);
+        fuse_sync_writes(inode);
+        mutex_unlock(&inode->i_mutex);
+
         req = fuse_get_req_nofail_nopages(fc, file);
         memset(&inarg, 0, sizeof(inarg));
         inarg.fh = ff->fh;
@@ -411,21 +467,6 @@ static int fuse_flush(struct file *file, fl_owner_t id)
         return err;
 }
 
-/*
- * Wait for all pending writepages on the inode to finish.
- *
- * This is currently done by blocking further writes with FUSE_NOWRITE
- * and waiting for all sent writes to complete.
- *
- * This must be called under i_mutex, otherwise the FUSE_NOWRITE usage
- * could conflict with truncation.
- */
-static void fuse_sync_writes(struct inode *inode)
-{
-        fuse_set_nowrite(inode);
-        fuse_release_nowrite(inode);
-}
-
 int fuse_fsync_common(struct file *file, loff_t start, loff_t end,
                       int datasync, int isdir)
 {
@@ -459,6 +500,12 @@ int fuse_fsync_common(struct file *file, loff_t start, loff_t end,
 
         fuse_sync_writes(inode);
 
+        if (test_bit(FUSE_I_MTIME_DIRTY, &get_fuse_inode(inode)->state)) {
+                int err = fuse_flush_mtime(file, false);
+                if (err)
+                        goto out;
+        }
+
         req = fuse_get_req_nopages(fc);
         if (IS_ERR(req)) {
                 err = PTR_ERR(req);
@@ -655,7 +702,33 @@ static void fuse_read_update_size(struct inode *inode, loff_t size,
         spin_unlock(&fc->lock);
 }
 
-static int fuse_readpage(struct file *file, struct page *page)
+static void fuse_short_read(struct fuse_req *req, struct inode *inode,
+                            u64 attr_ver)
+{
+        size_t num_read = req->out.args[0].size;
+        struct fuse_conn *fc = get_fuse_conn(inode);
+
+        if (fc->writeback_cache) {
+                /*
+                 * A hole in a file. Some data after the hole are in page cache,
+                 * but have not reached the client fs yet. So, the hole is not
+                 * present there.
+                 */
+                int i;
+                int start_idx = num_read >> PAGE_CACHE_SHIFT;
+                size_t off = num_read & (PAGE_CACHE_SIZE - 1);
+
+                for (i = start_idx; i < req->num_pages; i++) {
+                        zero_user_segment(req->pages[i], off, PAGE_CACHE_SIZE);
+                        off = 0;
+                }
+        } else {
+                loff_t pos = page_offset(req->pages[0]) + num_read;
+                fuse_read_update_size(inode, pos, attr_ver);
+        }
+}
+
+static int fuse_do_readpage(struct file *file, struct page *page)
 {
         struct fuse_io_priv io = { .async = 0, .file = file };
         struct inode *inode = page->mapping->host;
@@ -667,10 +740,6 @@ static int fuse_readpage(struct file *file, struct page *page)
         u64 attr_ver;
         int err;
 
-        err = -EIO;
-        if (is_bad_inode(inode))
-                goto out;
-
         /*
          * Page writeback can extend beyond the lifetime of the
          * page-cache page, so make sure we read a properly synced
@@ -679,9 +748,8 @@ static int fuse_readpage(struct file *file, struct page *page)
         fuse_wait_on_page_writeback(inode, page->index);
 
         req = fuse_get_req(fc, 1);
-        err = PTR_ERR(req);
         if (IS_ERR(req))
-                goto out;
+                return PTR_ERR(req);
 
         attr_ver = fuse_get_attr_version(fc);
 
@@ -692,18 +760,32 @@ static int fuse_readpage(struct file *file, struct page *page)
         req->page_descs[0].length = count;
         num_read = fuse_send_read(req, &io, pos, count, NULL);
         err = req->out.h.error;
-        fuse_put_request(fc, req);
 
         if (!err) {
                 /*
                  * Short read means EOF.  If file size is larger, truncate it
                  */
                 if (num_read < count)
-                        fuse_read_update_size(inode, pos + num_read, attr_ver);
+                        fuse_short_read(req, inode, attr_ver);
 
                 SetPageUptodate(page);
         }
 
+        fuse_put_request(fc, req);
+
+        return err;
+}
+
+static int fuse_readpage(struct file *file, struct page *page)
+{
+        struct inode *inode = page->mapping->host;
+        int err;
+
+        err = -EIO;
+        if (is_bad_inode(inode))
+                goto out;
+
+        err = fuse_do_readpage(file, page);
         fuse_invalidate_atime(inode);
  out:
         unlock_page(page);
@@ -726,13 +808,9 @@ static void fuse_readpages_end(struct fuse_conn *fc, struct fuse_req *req)
                 /*
                  * Short read means EOF. If file size is larger, truncate it
                  */
-                if (!req->out.h.error && num_read < count) {
-                        loff_t pos;
+                if (!req->out.h.error && num_read < count)
+                        fuse_short_read(req, inode, req->misc.read.attr_ver);
 
-                        pos = page_offset(req->pages[0]) + num_read;
-                        fuse_read_update_size(inode, pos,
-                                              req->misc.read.attr_ver);
-                }
                 fuse_invalidate_atime(inode);
         }
 
@@ -922,16 +1000,21 @@ static size_t fuse_send_write(struct fuse_req *req, struct fuse_io_priv *io,
         return req->misc.write.out.size;
 }
 
-void fuse_write_update_size(struct inode *inode, loff_t pos)
+bool fuse_write_update_size(struct inode *inode, loff_t pos)
 {
         struct fuse_conn *fc = get_fuse_conn(inode);
         struct fuse_inode *fi = get_fuse_inode(inode);
+        bool ret = false;
 
         spin_lock(&fc->lock);
         fi->attr_version = ++fc->attr_version;
-        if (pos > inode->i_size)
+        if (pos > inode->i_size) {
                 i_size_write(inode, pos);
+                ret = true;
+        }
         spin_unlock(&fc->lock);
+
+        return ret;
 }
 
 static size_t fuse_send_write_pages(struct fuse_req *req, struct file *file,
@@ -1116,6 +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;
@@ -1289,13 +1381,18 @@ static inline int fuse_iter_npages(const struct iov_iter *ii_p)
 
 ssize_t fuse_direct_io(struct fuse_io_priv *io, const struct iovec *iov,
                        unsigned long nr_segs, size_t count, loff_t *ppos,
-                       int write)
+                       int flags)
 {
+        int write = flags & FUSE_DIO_WRITE;
+        int cuse = flags & FUSE_DIO_CUSE;
         struct file *file = io->file;
+        struct inode *inode = file->f_mapping->host;
         struct fuse_file *ff = file->private_data;
         struct fuse_conn *fc = ff->fc;
         size_t nmax = write ? fc->max_write : fc->max_read;
         loff_t pos = *ppos;
+        pgoff_t idx_from = pos >> PAGE_CACHE_SHIFT;
+        pgoff_t idx_to = (pos + count - 1) >> PAGE_CACHE_SHIFT;
         ssize_t res = 0;
         struct fuse_req *req;
         struct iov_iter ii;
@@ -1309,6 +1406,14 @@ ssize_t fuse_direct_io(struct fuse_io_priv *io, const struct iovec *iov,
         if (IS_ERR(req))
                 return PTR_ERR(req);
 
+        if (!cuse && fuse_range_is_writeback(inode, idx_from, idx_to)) {
+                if (!write)
+                        mutex_lock(&inode->i_mutex);
+                fuse_sync_writes(inode);
+                if (!write)
+                        mutex_unlock(&inode->i_mutex);
+        }
+
         while (count) {
                 size_t nres;
                 fl_owner_t owner = current->files;
@@ -1397,7 +1502,8 @@ static ssize_t __fuse_direct_write(struct fuse_io_priv *io,
 
         res = generic_write_checks(file, ppos, &count, 0);
         if (!res)
-                res = fuse_direct_io(io, iov, nr_segs, count, ppos, 1);
+                res = fuse_direct_io(io, iov, nr_segs, count, ppos,
+                                     FUSE_DIO_WRITE);
 
         fuse_invalidate_attr(inode);
 
@@ -1885,6 +1991,77 @@ out:
         return err;
 }
 
+/*
+ * It's worthy to make sure that space is reserved on disk for the write,
+ * but how to implement it without killing performance need more thinking.
+ */
+static int fuse_write_begin(struct file *file, struct address_space *mapping,
+                loff_t pos, unsigned len, unsigned flags,
+                struct page **pagep, void **fsdata)
+{
+        pgoff_t index = pos >> PAGE_CACHE_SHIFT;
+        struct fuse_conn *fc = get_fuse_conn(file->f_dentry->d_inode);
+        struct page *page;
+        loff_t fsize;
+        int err = -ENOMEM;
+
+        WARN_ON(!fc->writeback_cache);
+
+        page = grab_cache_page_write_begin(mapping, index, flags);
+        if (!page)
+                goto error;
+
+        fuse_wait_on_page_writeback(mapping->host, page->index);
+
+        if (PageUptodate(page) || len == PAGE_CACHE_SIZE)
+                goto success;
+        /*
+         * Check if the start this page comes after the end of file, in which
+         * case the readpage can be optimized away.
+         */
+        fsize = i_size_read(mapping->host);
+        if (fsize <= (pos & PAGE_CACHE_MASK)) {
+                size_t off = pos & ~PAGE_CACHE_MASK;
+                if (off)
+                        zero_user_segment(page, 0, off);
+                goto success;
+        }
+        err = fuse_do_readpage(file, page);
+        if (err)
+                goto cleanup;
+success:
+        *pagep = page;
+        return 0;
+
+cleanup:
+        unlock_page(page);
+        page_cache_release(page);
+error:
+        return err;
+}
+
+static int fuse_write_end(struct file *file, struct address_space *mapping,
+                loff_t pos, unsigned len, unsigned copied,
+                struct page *page, void *fsdata)
+{
+        struct inode *inode = page->mapping->host;
+
+        if (!PageUptodate(page)) {
+                /* Zero any unwritten bytes at the end of the page */
+                size_t endoff = (pos + copied) & ~PAGE_CACHE_MASK;
+                if (endoff)
+                        zero_user_segment(page, endoff, PAGE_CACHE_SIZE);
+                SetPageUptodate(page);
+        }
+
+        fuse_write_update_size(inode, pos + copied);
+        set_page_dirty(page);
+        unlock_page(page);
+        page_cache_release(page);
+
+        return copied;
+}
+
 static int fuse_launder_page(struct page *page)
 {
         int err = 0;
@@ -1946,20 +2123,9 @@ static const struct vm_operations_struct fuse_file_vm_ops = {
 
 static int fuse_file_mmap(struct file *file, struct vm_area_struct *vma)
 {
-        if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE)) {
-                struct inode *inode = file_inode(file);
-                struct fuse_conn *fc = get_fuse_conn(inode);
-                struct fuse_inode *fi = get_fuse_inode(inode);
-                struct fuse_file *ff = file->private_data;
-                /*
-                 * file may be written through mmap, so chain it onto the
-                 * inodes's write_file list
-                 */
-                spin_lock(&fc->lock);
-                if (list_empty(&ff->write_entry))
-                        list_add(&ff->write_entry, &fi->write_files);
-                spin_unlock(&fc->lock);
-        }
+        if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
+                fuse_link_write_file(file);
+
         file_accessed(file);
         vma->vm_ops = &fuse_file_vm_ops;
         return 0;
@@ -2606,7 +2772,7 @@ static void fuse_register_polled_file(struct fuse_conn *fc,
 {
         spin_lock(&fc->lock);
         if (RB_EMPTY_NODE(&ff->polled_node)) {
-                struct rb_node **link, *parent;
+                struct rb_node **link, *uninitialized_var(parent);
 
                 link = fuse_find_polled_node(fc, ff->kh, &parent);
                 BUG_ON(*link);
@@ -2850,8 +3016,16 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
                 goto out;
 
         /* we could have extended the file */
-        if (!(mode & FALLOC_FL_KEEP_SIZE))
-                fuse_write_update_size(inode, offset + length);
+        if (!(mode & FALLOC_FL_KEEP_SIZE)) {
+                bool changed = fuse_write_update_size(inode, offset + length);
+
+                if (changed && fc->writeback_cache) {
+                        struct fuse_inode *fi = get_fuse_inode(inode);
+
+                        inode->i_mtime = current_fs_time(inode->i_sb);
+                        set_bit(FUSE_I_MTIME_DIRTY, &fi->state);
+                }
+        }
 
         if (mode & FALLOC_FL_PUNCH_HOLE)
                 truncate_pagecache_range(inode, offset, offset + length - 1);
@@ -2915,6 +3089,8 @@ static const struct address_space_operations fuse_file_aops  = {
         .set_page_dirty = __set_page_dirty_nobuffers,
         .bmap           = fuse_bmap,
         .direct_IO      = fuse_direct_IO,
+        .write_begin    = fuse_write_begin,
+        .write_end      = fuse_write_end,
 };
 
 void fuse_init_file_inode(struct inode *inode)
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 2da5db2c8bdb..a257ed8ebee6 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -119,6 +119,8 @@ enum {
         FUSE_I_INIT_RDPLUS,
         /** An operation changing file size is in progress  */
         FUSE_I_SIZE_UNSTABLE,
+        /** i_mtime has been updated locally; a flush to userspace needed */
+        FUSE_I_MTIME_DIRTY,
 };
 
 struct fuse_conn;
@@ -480,6 +482,9 @@ struct fuse_conn {
         /** Set if bdi is valid */
         unsigned bdi_initialized:1;
 
+        /** write-back cache policy (default is write-through) */
+        unsigned writeback_cache:1;
+
         /*
          * The following bitfields are only for optimization purposes
          * and hence races in setting them will not cause malfunction
@@ -863,9 +868,20 @@ int fuse_reverse_inval_entry(struct super_block *sb, u64 parent_nodeid,
 
 int fuse_do_open(struct fuse_conn *fc, u64 nodeid, struct file *file,
                  bool isdir);
+
+/**
+ * fuse_direct_io() flags
+ */
+
+/** If set, it is WRITE; otherwise - READ */
+#define FUSE_DIO_WRITE (1 << 0)
+
+/** CUSE pass fuse_direct_io() a file which f_mapping->host is not from FUSE */
+#define FUSE_DIO_CUSE  (1 << 1)
+
 ssize_t fuse_direct_io(struct fuse_io_priv *io, const struct iovec *iov,
                        unsigned long nr_segs, size_t count, loff_t *ppos,
-                       int write);
+                       int flags);
 long fuse_do_ioctl(struct file *file, unsigned int cmd, unsigned long arg,
                    unsigned int flags);
 long fuse_ioctl_common(struct file *file, unsigned int cmd,
@@ -873,7 +889,9 @@ long fuse_ioctl_common(struct file *file, unsigned int cmd,
 unsigned fuse_file_poll(struct file *file, poll_table *wait);
 int fuse_dev_release(struct inode *inode, struct file *file);
 
-void fuse_write_update_size(struct inode *inode, loff_t pos);
+bool fuse_write_update_size(struct inode *inode, loff_t pos);
+
+int fuse_flush_mtime(struct file *file, bool nofail);
 
 int fuse_do_setattr(struct inode *inode, struct iattr *attr,
                     struct file *file);
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 9c761b611c54..b4bff1b15028 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -170,8 +170,11 @@ void fuse_change_attributes_common(struct inode *inode, struct fuse_attr *attr,
         inode->i_blocks  = attr->blocks;
         inode->i_atime.tv_sec   = attr->atime;
         inode->i_atime.tv_nsec  = attr->atimensec;
-        inode->i_mtime.tv_sec   = attr->mtime;
-        inode->i_mtime.tv_nsec  = attr->mtimensec;
+        /* mtime from server may be stale due to local buffered write */
+        if (!fc->writeback_cache || !S_ISREG(inode->i_mode)) {
+                inode->i_mtime.tv_sec   = attr->mtime;
+                inode->i_mtime.tv_nsec  = attr->mtimensec;
+        }
         inode->i_ctime.tv_sec   = attr->ctime;
         inode->i_ctime.tv_nsec  = attr->ctimensec;
 
@@ -197,6 +200,7 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
 {
         struct fuse_conn *fc = get_fuse_conn(inode);
         struct fuse_inode *fi = get_fuse_inode(inode);
+        bool is_wb = fc->writeback_cache;
         loff_t oldsize;
         struct timespec old_mtime;
 
@@ -211,10 +215,16 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr,
         fuse_change_attributes_common(inode, attr, attr_valid);
 
         oldsize = inode->i_size;
-        i_size_write(inode, attr->size);
+        /*
+         * In case of writeback_cache enabled, the cached writes beyond EOF
+         * extend local i_size without keeping userspace server in sync. So,
+         * attr->size coming from server can be stale. We cannot trust it.
+         */
+        if (!is_wb || !S_ISREG(inode->i_mode))
+                i_size_write(inode, attr->size);
         spin_unlock(&fc->lock);
 
-        if (S_ISREG(inode->i_mode)) {
+        if (!is_wb && S_ISREG(inode->i_mode)) {
                 bool inval = false;
 
                 if (oldsize != attr->size) {
@@ -243,6 +253,8 @@ static void fuse_init_inode(struct inode *inode, struct fuse_attr *attr)
 {
         inode->i_mode = attr->mode & S_IFMT;
         inode->i_size = attr->size;
+        inode->i_mtime.tv_sec  = attr->mtime;
+        inode->i_mtime.tv_nsec = attr->mtimensec;
         if (S_ISREG(inode->i_mode)) {
                 fuse_init_common(inode);
                 fuse_init_file_inode(inode);
@@ -289,7 +301,9 @@ struct inode *fuse_iget(struct super_block *sb, u64 nodeid,
                 return NULL;
 
         if ((inode->i_state & I_NEW)) {
-                inode->i_flags |= S_NOATIME|S_NOCMTIME;
+                inode->i_flags |= S_NOATIME;
+                if (!fc->writeback_cache || !S_ISREG(inode->i_mode))
+                        inode->i_flags |= S_NOCMTIME;
                 inode->i_generation = generation;
                 inode->i_data.backing_dev_info = &fc->bdi;
                 fuse_init_inode(inode, attr);
@@ -873,6 +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;
@@ -900,7 +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