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SubjectRe: O_DIRECT
On Tue, 20 Jul 2004 10:27:57 -0700
Shesha Sreenivasamurthy <shesha@inostor.com> wrote:

Hi Shesha,

> I am having trouble with O_DIRECT. Trying to read or write from a block
> device partition.
>
> 1. Can O_DIRECT be used on a plain block device partition say
> "/dev/sda11" without having a filesystem on it.

yes.

> 2. If no file system is created then what should be the softblock size.
> I am using the IOCTL "BLKBSZGET". Is this correct?

yes.

> 3. Can we use SEEK_END with O_DIRECT on a partition without filesystem.

yes.

I'm using these exact things in an application.

Note that with 2.4 kernels the "granularity" you can use for offset
and r/w size is the softblock size (*). For 2.6 the requirements are
much more relaxed: it's the device blocksize (typically 512 byte).

(*): actually one of offset or r/w size has a smaller minimum if
I remember correctly. Don't remember which one. But if you assume
the softblock size as a minimum for both you're allways safe.

greetings,
Rob van Nieuwkerk
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