Do filp open

http://lxr.free-electrons.com/source/fs/namei.c#L3223

3223 struct file *do_filp_open(int dfd, struct filename *pathname,
3224                 const struct open_flags *op)
3225 {
3226         struct nameidata nd;
3227         int flags = op->lookup_flags;
3228         struct file *filp;
3229 
3230         filp = path_openat(dfd, pathname, &nd, op, flags | LOOKUP_RCU);
3231         if (unlikely(filp == ERR_PTR(-ECHILD)))
3232                 filp = path_openat(dfd, pathname, &nd, op, flags);
3233         if (unlikely(filp == ERR_PTR(-ESTALE)))
3234                 filp = path_openat(dfd, pathname, &nd, op, flags | LOOKUP_REVAL);
3235         return filp;
3236 }