fuse: Trust kernel i_size only

Make fuse think that when writeback is on the inode's i_size is always
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.

fuse_file_fallocate() is also fixed because now we should keep i_size up to
date, so it must be updated if FUSE_FALLOCATE request succeeded.

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

3 files changed, 39 insertions, 6 deletions

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 1d1292c581c3..c52f143da9ad 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -839,6 +839,11 @@ 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);
 
         stat->dev = inode->i_sb->s_dev;
         stat->ino = attr->ino;
@@ -1580,6 +1585,7 @@ 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;
 
@@ -1651,7 +1657,9 @@ int fuse_do_setattr(struct inode *inode, struct iattr *attr,
         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 +1671,8 @@ 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);
         }
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 592d7b48e421..c091a17d3ffc 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -675,9 +675,26 @@ 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);
 
-        loff_t pos = page_offset(req->pages[0]) + num_read;
-        fuse_read_update_size(inode, pos, attr_ver);
+                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_readpage(struct file *file, struct page *page)
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index d468643a68b2..c668c8436894 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -197,6 +197,7 @@ 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 +212,16 @@ 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) {