Re: [RFC] server's statd and lockd will not sync after its nfslock restart

[Trond Myklebust <trond.myklebust@fys.uio.no>]

On Thu, 2009-12-17 at 15:34 -0500, Chuck Lever wrote: 
> On Dec 17, 2009, at 3:27 PM, Trond Myklebust wrote:
> > One alternative might be to just record the kernel's random boot_id in
> > the pid file. That gets regenerated on each boot, so should be unique.
> 
> Where do you get it in user space?  Is it available on earlier  
> kernels?  ("should be unique" -- I hope it doesn't have the same  
> problem we had with XID replay on diskless systems).

You can access it from userland as the 'kernel.random.boot_id' sysctl.

It is available on 2.4 kernels and newer.

It is based on the kernel random number generator, so should be
reasonably unique.

> Fwiw, I tried using the boot time stamp at one point, but  
> unfortunately that's adjusted by the ntp offset, so it can take  
> different values over time.  It was difficult to compare it to a time  
> stamp recorded in a file.

Agreed. You can't rely on time stamps.

Trond