Re: [PATCH,RESEND] make knfsd interact cleanly with HSMs

[Neil Brown <neilb@suse.de>]

On Friday May 5, gnb@sgi.com wrote:
> 
> This patch seeks to remedy the interaction between knfsd and HSMs by
> providing mechanisms to allow knfsd to tell an underlying filesystem
> (which supports HSMs) not to block for reads, writes and truncates
> of offline files.  It's a port of a Linux 2.4 patch used in SGI's
> ProPack distro since 2004 and in SLES9 since SP2.  The patch:
> 
> *  provides a new ATTR_NO_BLOCK flag which the kernel can
>    use to tell a filesystem's inode_ops->setattr() operation not
>    to block when truncating an offline file.  XFS already obeys
>    this flag (inside a #ifdef)
> 
> *  changes knfsd to provide ATTR_NO_BLOCK when it does the VFS
>    calls to implement the SETATTR NFS call.
> 
> *  changes knfsd to supply the O_NONBLOCK flag in the temporary
>    struct file it uses for VFS reads and writes, in order to ask
>    the filesystem not to block when reading or writing an offline
>    file.  XFS already obeys this new semantic for O_NONBLOCK
>    (and in SLES9 so does JFS).
> 
> *  adds code to translate the -EAGAIN the filesystem returns when
>    it would have blocked, to the -ETIMEDOUT that knfsd expects.
> 

Yes, I'm happy with this.  All the changes make sense and look right.

Thanks for persisting with it.

I'll send it on up the chain...

NeilBrown