Memory alignment requirement for Direct/IO

Memory alignment requirement for Direct/IO

[Xiaoli Feng]

Hello,

I setup samba server in upstream  and mount it in local with cache=none,vers=3.11. Then test
the Direct/IO function like this:

fd=open(fname, O_DIRECT | O_RDWR | O_CREAT, 0666))
lseek(fd, 0, SEEK_SET);
read(fd, buf, 1);

For local filesystem such as XFS, "read" will be failed because XFS has 512Byte memory aligment
for Direct/IO. But it's success for cifs. I don't know if it's expected. Could anybody tell me
more about Direct/IO for cifs?

Thanks.

-- 
Best regards!
XiaoLi Feng 冯小丽

Red Hat Software (Beijing) Co.,Ltd
filesystem-qe Team
IRC:xifeng，#channel: fs-qe
Tel:+86-10-8388112
9/F, Raycom

Re: Memory alignment requirement for Direct/IO

[Steve French]

I would expect direct i/o to work with unaligned reads over SMB3 mounts.

Let me know if you see different behavior to any servers.

On Tue, Apr 30, 2019 at 4:01 AM Xiaoli Feng <xifeng@redhat.com> wrote:
>
> Hello,
>
> I setup samba server in upstream  and mount it in local with cache=none,vers=3.11. Then test
> the Direct/IO function like this:
>
> fd=open(fname, O_DIRECT | O_RDWR | O_CREAT, 0666))
> lseek(fd, 0, SEEK_SET);
> read(fd, buf, 1);
>
> For local filesystem such as XFS, "read" will be failed because XFS has 512Byte memory aligment
> for Direct/IO. But it's success for cifs. I don't know if it's expected. Could anybody tell me
> more about Direct/IO for cifs?
>
> Thanks.
>
> --
> Best regards!
> XiaoLi Feng 冯小丽
>
> Red Hat Software (Beijing) Co.,Ltd
> filesystem-qe Team
> IRC:xifeng，#channel: fs-qe
> Tel:+86-10-8388112
> 9/F, Raycom



-- 
Thanks,

Steve