SMB2 AIO with unaligned memory address caused the read data corruption.

[Volker Lendecke]

On Mon, Jun 11, 2018 at 12:21:57PM -0700, Partha Sarathi via samba-technical wrote:
> We recently come across a read data corruption issue using samba.4.7.x
> against *Linux Fuse FS with DIO enabled*.
> 
> We nailed down the issue was an outcome of samba AIO preads were reusing
> the unaligned buffer address allocated by *talloc* library.  The kernel
> FUSE with DIO path (Direct IO) was not handling the unaligned memory
> correctly.  We are trying to fix this issue from both the ends.

As Jeremy wrote, there must be something non-obvious to us going on.
Maybe you want to post your complete Samba source code somewhere.  To
the best of our knowledge, pread/pwrite don't have alignment
requirements, and that is what we're using.

If you have more direct access into fuse using other calls, things
might be different. This would be highly interesting, as many
fuse-based Samba servers suffer from bad performance. If you have
tweaks there that could help us, we'd appreciate those patches.

Thanks, Volker

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