[PATCH] cifs: flush before set-info if we have writeable handles

[Ronnie Sahlberg <lsahlber@redhat.com>]

Servers can defer destaging any data and updating the mtime until close().
This means that if we do a setinfo to modify the mtime while other handles
are open for write the server may overwrite our setinfo timestamps when
if flushes the file on close() of the writeable handle.

To avoid this we add an explicit flush() before any attempts to use setinfo
and update the mtime IF we have writeable handles open.

This makes "cp -p" preserve the mtime when copying files to some smb servers.

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
---
 fs/cifs/smb2inode.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/fs/cifs/smb2inode.c b/fs/cifs/smb2inode.c
index 278405d26c47..a3603ec3a086 100644
--- a/fs/cifs/smb2inode.c
+++ b/fs/cifs/smb2inode.c
@@ -516,7 +516,11 @@ smb2_set_file_info(struct inode *inode, const char *full_path,
 {
 	struct cifs_sb_info *cifs_sb = CIFS_SB(inode->i_sb);
 	struct tcon_link *tlink;
+	struct cifs_tcon *tcon;
+	struct TCP_Server_Info *server;
 	int rc;
+	struct cifsInodeInfo *cifsi;
+	struct cifsFileInfo *wrcfile;
 
 	if ((buf->CreationTime == 0) && (buf->LastAccessTime == 0) &&
 	    (buf->LastWriteTime == 0) && (buf->ChangeTime == 0) &&
@@ -527,7 +531,19 @@ smb2_set_file_info(struct inode *inode, const char *full_path,
 	if (IS_ERR(tlink))
 		return PTR_ERR(tlink);
 
-	rc = smb2_compound_op(xid, tlink_tcon(tlink), cifs_sb, full_path,
+	tcon = tlink_tcon(tlink);
+	server = tcon->ses->server;
+
+	if (buf->LastWriteTime) {
+		cifsi = CIFS_I(inode);
+		wrcfile = find_writable_file(cifsi, false);
+		if (wrcfile) {
+			filemap_write_and_wait(inode->i_mapping);
+			server->ops->flush(xid, tcon, &wrcfile->fid);
+			cifsFileInfo_put(wrcfile);
+		}
+	}
+	rc = smb2_compound_op(xid, tcon, cifs_sb, full_path,
 			      FILE_WRITE_ATTRIBUTES, FILE_OPEN, 0, buf,
 			      SMB2_OP_SET_INFO);
 	cifs_put_tlink(tlink);
-- 
2.13.6