Re: O_DIRECT wierd behavior..

[Suresh Gopalakrishnan]

On Sun, 16 Dec 2001, Terje Eggestad wrote:
> The problem is that the kernel that don't support O_DIRECT has
> erronous handling of the O_DIRECT flag. Meaning they happily accept
> it. In order to figure out ifthe running kernel support O_DIRECT you
> MUST attempt an unaligned read/write, if it succed the kernel DON'T
> support O_DIRECT. TJ

You are right! It went through on 2.4.2 even with an unaligned buffer.

So direct i/o has to be multiple of page size blocks, from page aligned
buffer, and apparently into page aligned offset in the file! Is this the
expected behavior?

--suresh

> > Thanks for the patches. There seems to be one more fix required: the test
> > program below works in 2.4.16 only if the write size is a multiple of 4K.
> > (Why) are all writes expected to be page size, in addition to being page
> > aligned? (It works fine on 2.4.2 for all sizes). Any quick fixes? :)
> > --suresh