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Re: [Xen-devel] [PATCH v3] tools/xenconsoled: Increase file descriptor limit

Andrew Cooper writes ("Re: [PATCH v3] tools/xenconsoled: Increase file 
descriptor limit"):
> On 19/02/15 16:30, Ian Jackson wrote:
> > Why is this only a stopgap solution ?
> It is yet another place with an arbitrary limit, which is one more
> moving part to go wrong.

OIC.  I meant `unlimited', but...

> >>> As Xenconsoled genuinely needs a large number of file descriptors
> >>> if a large number of domains are running, and is well behaved with
> >>> its descriptors, attempt to up the limit to the system maximum.
> > Perhaps you mean it should be "unlimited" but that doesn't seem right
> > either.
> Where do I perhaps mean "unlimited"?
> Attempting to set NOFILE with RLIM_INFINITY is an unconditional failure,
> and there is unfortunately no RLIM_SYSTEM_MAX.


I think this is a bug in Linux.


      The limit specified to setrlimit() would have raised the maximum
      limit value, and the calling process does not have appropriate

But that's not what's happening, or at least, it's a contorted

Best in shell is using `sysctl':
   ulimit -H -n "$(sysctl -n fs.nr_open)"
But not very portable.

So I am now convinced this should be done in C :-/.

> > The value should be some multiple of the maximum number of
> > domains.
> The maximum number of domains (limited by the domid abi) is 32751
> That would put the number of fds needed at 131004 + overhead (20
> perhaps?).  This is substantially larger than the default on Linux, but
> within the default system max of 2^20.

Considering this, and looking at your actual code I think you should
simply set the value to 131004[1] (plus say 1000 spare for libc use
and so on) and not bother with trying to find the system maximum.

It would be nice to warn if the attempt fails.

[1] Computed from appropriate #defines.


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