Path openat

http://lxr.free-electrons.com/source/fs/namei.c#L3152

3152 static struct file *path_openat(int dfd, struct filename *pathname,
3153                 struct nameidata *nd, const struct open_flags *op, int flags)
3154 {
3155         struct file *base = NULL;
3156         struct file *file;
3157         struct path path;
3158         int opened = 0;
3159         int error;
3160 
3161         file = get_empty_filp();
3162         if (IS_ERR(file))
3163                 return file;
3164 
3165         file->f_flags = op->open_flag;
3166 
3167         if (unlikely(file->f_flags & __O_TMPFILE)) {
3168                 error = do_tmpfile(dfd, pathname, nd, flags, op, file, &opened);
3169                 goto out;
3170         }
3171 
3172         error = path_init(dfd, pathname->name, flags | LOOKUP_PARENT, nd, &base);
3173         if (unlikely(error))
3174                 goto out;
3175 
3176         current->total_link_count = 0;
3177         error = link_path_walk(pathname->name, nd);
3178         if (unlikely(error))
3179                 goto out;
3180 
3181         error = do_last(nd, &path, file, op, &opened, pathname);
3182         while (unlikely(error > 0)) { /* trailing symlink */
3183                 struct path link = path;
3184                 void *cookie;
3185                 if (!(nd->flags & LOOKUP_FOLLOW)) {
3186                         path_put_conditional(&path, nd);
3187                         path_put(&nd->path);
3188                         error = -ELOOP;
3189                         break;
3190                 }
3191                 error = may_follow_link(&link, nd);
3192                 if (unlikely(error))
3193                         break;
3194                 nd->flags |= LOOKUP_PARENT;
3195                 nd->flags &= ~(LOOKUP_OPEN|LOOKUP_CREATE|LOOKUP_EXCL);
3196                 error = follow_link(&link, nd, &cookie);
3197                 if (unlikely(error))
3198                         break;
3199                 error = do_last(nd, &path, file, op, &opened, pathname);
3200                 put_link(nd, &link, cookie);
3201         }
3202 out:
3203         if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT))
3204                 path_put(&nd->root);
3205         if (base)
3206                 fput(base);
3207         if (!(opened & FILE_OPENED)) {
3208                 BUG_ON(!error);
3209                 put_filp(file);
3210         }
3211         if (unlikely(error)) {
3212                 if (error == -EOPENSTALE) {
3213                         if (flags & LOOKUP_RCU)
3214                                 error = -ECHILD;
3215                         else
3216                                 error = -ESTALE;
3217                 }
3218                 file = ERR_PTR(error);
3219         }
3220         return file;
3221 }