CIFS: Check for mandatory brlocks on read/write

Currently CIFS code accept read/write ops on mandatory locked area
when two processes use the same file descriptor - it's wrong.
Fix this by serializing io and brlock operations on the inode.

Signed-off-by: Pavel Shilovsky <pshilovsky@etersoft.ru>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/cifsproto.h

@@ -180,6 +180,10 @@ extern struct smb_vol *cifs_get_volume_info(char *mount_data,
 extern int cifs_mount(struct cifs_sb_info *, struct smb_vol *);
 extern void cifs_umount(struct cifs_sb_info *);
 extern void cifs_mark_open_files_invalid(struct cifs_tcon *tcon);
+extern bool cifs_find_lock_conflict(struct cifsFileInfo *cfile, __u64 offset,
+				    __u64 length, __u8 type,
+				    struct cifsLockInfo **conf_lock,
+				    bool rw_check);
 
 #if IS_ENABLED(CONFIG_CIFS_DFS_UPCALL)
 extern void cifs_dfs_release_automount_timer(void);