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>

1 files changed, 11 insertions, 2 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);
         }