[linux-cifs-client] mount.cifs O_DIRECT or directio

[Andrew Chernow]

I am looking to perform directio on a cifs mount.  I tried using O_DIRECT, as I 
did with block devices and nfs mounts successfully.  The cifs mount gave me an 
EINVAL error on open(2) when I supplied the O_DIRECT flag.  After further 
research, I found the directio mount option.

The goal is to not cache anything on the mount host.  When I issue a mkdir(), 
write(), read(), unlink(), etc... I need these to communicate directly with the 
target of the mount.  I don't want anything cached locally.

mount.cifs version: 1.10-3.0.23c
kernel version: 2.6.9-42.0.3.EL (CentOS 32-bit)

NOTE: also tried kernel 2.6.14 running on a gentoo machine, same results.

Questions:
Does mount.cifs implement O_DIRECT via the directio mount option?

Will directio give me the same functionality as O_DIRECT would?  Meaning, with 
'mount.cifs -o directio', do I even need O_DIRECT as I would with a block device?

Are there any alignment requirements with directio as there are with O_DIRECT?

Are there any other mount.cifs options I should be aware of; considering what I 
am trying to do?

Should I use O_SYNC and O_RSYNC along with the directio mount option?

andrew