请教：哪种方式能保证文件系统数据完整写入磁盘？sync or direct IO or 其它？

Tinnal

回复 1# humjb_1983

http://stackoverflow.com/questio ... en2-different-alike

O_DIRECT alone only promises that the kernel will avoid copying data from user space to kernel space, and will instead write it directly via DMA (if possible). Data does not go into caches. There is no strict guarantee that the function will return only after all data has been transferred.

O_SYNC guarantees that the call will not return before all data has been transferred to the disk (as far as the OS can tell). This still does not guarantee that the data isn't somewhere in the harddisk write cache, but it is as much as the OS can guarantee.

O_DIRECT|O_SYNC is the combination of these, i.e. "DMA + guarantee".

Tinnal

回复 1# humjb_1983


    最近很少上来呀。 特别的，这两种方法，如果是采用mmap文件的方式，就都不能实现直接写到硬盘。

Tinnal

回复 4# humjb_1983


   安stackoverflow的解析应该是这样的。O_DIRECT，从英文直译来说，也只体现直接，而非同步。体现的是免拷贝。

Tinnal

但我也没有去翻内核代码，有时候Linux常做得比承诺的要好。