[PATCH 6/10] fuse: Trust kernel i_size only

[Pavel Emelyanov <xemul@parallels.com>]

Make fuse think that when writeback is on the inode's i_size is alway up-to-date
and not update it with the value received from the userspace. This is done because
the page cache code may update i_size without letting the FS know.

This assumption implies fixing the previously introduced short-read helper -- when
a short read occurs the 'hole' is filled with zeroes.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
---
 fs/fuse/dir.c   |   10 ++++++----
 fs/fuse/file.c  |   23 +++++++++++++++++++++--
 fs/fuse/inode.c |    6 ++++--
 3 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 334e0b1..032fb20 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -790,7 +790,7 @@ static void fuse_fillattr(struct inode *inode, struct fuse_attr *attr,
 	stat->mtime.tv_nsec = attr->mtimensec;
 	stat->ctime.tv_sec = attr->ctime;
 	stat->ctime.tv_nsec = attr->ctimensec;
-	stat->size = attr->size;
+	stat->size = i_size_read(inode);
 	stat->blocks = attr->blocks;
 
 	if (attr->blksize != 0)
@@ -1350,7 +1350,7 @@ static int fuse_do_setattr(struct dentry *entry, struct iattr *attr,
 	struct fuse_req *req;
 	struct fuse_setattr_in inarg;
 	struct fuse_attr_out outarg;
-	bool is_truncate = false;
+	bool is_truncate = false, is_wb = fc->writeback_cache;
 	loff_t oldsize;
 	int err;
 
@@ -1423,7 +1423,8 @@ static int fuse_do_setattr(struct dentry *entry, struct iattr *attr,
 	fuse_change_attributes_common(inode, &outarg.attr,
 				      attr_timeout(&outarg));
 	oldsize = inode->i_size;
-	i_size_write(inode, outarg.attr.size);
+	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 */
@@ -1435,7 +1436,8 @@ static int fuse_do_setattr(struct dentry *entry, 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, oldsize, outarg.attr.size);
 		invalidate_inode_pages2(inode->i_mapping);
 	}
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 47f0f2e..9bc1390 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -541,9 +541,28 @@ static void fuse_read_update_size(struct inode *inode, loff_t size,
 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.
+		 */
+		int i;
+		size_t off = num_read & (PAGE_CACHE_SIZE - 1);
+
+		for (i = num_read >> PAGE_CACHE_SHIFT; i < req->num_pages; i++) {
+			struct page *page = req->pages[i];
+			void *mapaddr = kmap_atomic(page, KM_USER0);
 
-	loff_t pos = page_offset(req->pages[0]) + num_read;
-	fuse_read_update_size(inode, pos, attr_ver);
+			memset(mapaddr + off, 0, PAGE_CACHE_SIZE - off);
+
+			kunmap_atomic(mapaddr, KM_USER0);
+			off = 0;
+		}
+	} else {
+		loff_t pos = page_offset(req->pages[0]) + num_read;
+		fuse_read_update_size(inode, pos, attr_ver);
+	}
 }
 
 static int fuse_readpage(struct file *file, struct page *page)
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 1cd6165..88c577f 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -196,6 +196,7 @@ 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;
 
 	spin_lock(&fc->lock);
@@ -207,10 +208,11 @@ 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);
+	if (!is_wb || !S_ISREG(inode->i_mode))
+		i_size_write(inode, attr->size);
 	spin_unlock(&fc->lock);
 
-	if (S_ISREG(inode->i_mode) && oldsize != attr->size) {
+	if (!is_wb && S_ISREG(inode->i_mode) && oldsize != attr->size) {
 		truncate_pagecache(inode, oldsize, attr->size);
 		invalidate_inode_pages2(inode->i_mapping);
 	}
-- 
1.5.5.6