我怎么可以用O_DIRECT或O_SYNC外接SD卡采用Android奇巧 [英] How can I use O_DIRECT or O_SYNC on an external SD card with Android KitKat

问题描述

我的一个公司，使包括一个硬件加密引擎的SD存储卡。我们与写入/读取到一个特殊的文件加密模块进行交互。

I work for a company that makes an SD memory card that includes a hardware encryption engine. We interact with the encryption module by writing/reading to a special file.

与奇巧，在 O_DIRECT 标志开始似乎并没有在外部SD卡的支持。如果没有 O_DIRECT或O_SYNC 的支持，操作系统将返回缓存的数据，当我们读取SD卡（通过我们的特殊文件）加密引擎的响应。

Starting with KitKat, the O_DIRECT flag does not seem to be supported on the external SD card. Without O_DIRECT or O_SYNC support, the OS will returned cached data when we read the encryption engine's response from the SD card (via our special file).

是否有程序打开永恒的SD卡上的文件，读/写，有两种 O_DIRECT或O_SYNC ？

Is there a procedure to open a file on the eternal SD card, read/write, with either O_DIRECT or O_SYNC?

推荐答案

如果你有root访问到您的手机，你可以写一个1到的/ proc / sys目录/ VM / drop_caches清除页面缓存（见的 http://linux-mm.org/Drop_Caches ）。该命令之后的下一个读出的SD卡将返回非缓存的内容

If you have root-access to your phone you can write a 1 to /proc/sys/vm/drop_caches to clear the page cache (see http://linux-mm.org/Drop_Caches). After that command the next read on the sdcard will return the non-cached data.

有关股权设备（如您没有权限的/ proc / sys目录/ VM / drop_caches）有一个在AOSP一个问题（你可以加注星标）： 的https：//$c$c.google.com/p /安卓/问题/详细信息？ID = 67406

For stock-devices (where you have no permission to /proc/sys/vm/drop_caches) there is a issue in the AOSP (you may star it): https://code.google.com/p/android/issues/detail?id=67406

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