[CIFS] Allow local filesize for file that is open for write to be updated

from server when mount forcedirectio.

Allowing update of file size with non forcedirectio mounts should be
allowed in the fiture but requires carefully writing out the
last page in the local file if it is a partial page in order to
avoid corruption and careful serialization

Thanks to Maximiliano Curia who suggested similar changes and provided
a testcase.

Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index c249b628fd1c..670ec1e84da0 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -1835,10 +1835,20 @@ int is_size_safe_to_change(struct cifsInodeInfo *cifsInode)
                 open_file =  find_writable_file(cifsInode);
  
         if(open_file) {
+                struct cifs_sb_info *cifs_sb;
+
                 /* there is not actually a write pending so let
                 this handle go free and allow it to
                 be closable if needed */
                 atomic_dec(&open_file->wrtPending);
+
+                cifs_sb = CIFS_SB(cifsInode->vfs_inode.i_sb);
+                if ( cifs_sb->mnt_cifs_flags & CIFS_MOUNT_DIRECT_IO ) {
+                        /* since no page cache to corrupt on directio 
+                        we can change size safely */
+                        return 1;
+                }
+
                 return 0;
         } else
                 return 1;