[libvirt] [PATCH v2] qemu: add a max_core setting to qemu.conf for core dump size

[Daniel P. Berrange]

On Tue, Jul 12, 2016 at 12:53:18PM +0200, Martin Kletzander wrote:
> On Tue, Jul 12, 2016 at 10:56:53AM +0100, Daniel P. Berrange wrote:
> > On Tue, Jul 12, 2016 at 11:38:22AM +0200, Martin Kletzander wrote:
> > > On Tue, Jul 12, 2016 at 10:12:36AM +0100, Daniel P. Berrange wrote:
> > > > Currently the QEMU processes inherit their core dump rlimit
> > > > from libvirtd, which is really suboptimal. This change allows
> > > > their limit to be directly controller from qemu.conf instead.
> 
> s/controller/controlled/
> 
> > > > ---
> > > >
> > > > Changed in v2:
> > > >
> > > > - Allow use of string "unlimited"
> > > >
> > > > src/libvirt_private.syms           |  2 ++
> > > > src/qemu/libvirtd_qemu.aug         |  1 +
> > > > src/qemu/qemu.conf                 | 16 +++++++++++++++-
> > > > src/qemu/qemu_conf.c               | 17 +++++++++++++++++
> > > > src/qemu/qemu_conf.h               |  1 +
> > > > src/qemu/qemu_process.c            |  1 +
> > > > src/qemu/test_libvirtd_qemu.aug.in |  1 +
> > > > src/util/vircommand.c              | 14 ++++++++++++++
> > > > src/util/vircommand.h              |  1 +
> > > > src/util/virprocess.c              | 36 ++++++++++++++++++++++++++++++++++++
> > > > src/util/virprocess.h              |  1 +
> > > > 11 files changed, 90 insertions(+), 1 deletion(-)
> > > >
> > > 
> > > [...]
> > > 
> > > > diff --git a/src/qemu/libvirtd_qemu.aug b/src/qemu/libvirtd_qemu.aug
> > > > index 8bc23ba..a8edc2b 100644
> > > > --- a/src/qemu/libvirtd_qemu.aug
> > > > +++ b/src/qemu/libvirtd_qemu.aug
> > > > @@ -72,6 +72,7 @@ module Libvirtd_qemu =
> > > >                  | bool_entry "set_process_name"
> > > >                  | int_entry "max_processes"
> > > >                  | int_entry "max_files"
> > > > +                 | int_entry "max_core"
> > > 
> > > This should be expanded to allow "unlimited" as well.
> > 
> > Opps, yes.
> > 
> > > > diff --git a/src/qemu/qemu_conf.h b/src/qemu/qemu_conf.h
> > > > index 510cd9a..b730202 100644
> > > > --- a/src/qemu/qemu_conf.h
> > > > +++ b/src/qemu/qemu_conf.h
> > > > @@ -148,6 +148,7 @@ struct _virQEMUDriverConfig {
> > > >
> > > >     unsigned int maxProcesses;
> > > >     unsigned int maxFiles;
> > > > +    unsigned long long maxCore;
> > > >
> > > 
> > > This is not initialized anywhere, effectively making the limit default
> > > to 0 IIUC.
> > 
> > Yes, that's correct as per the qemu.conf docs - we don't allow
> > core dumps by default, since they can be absolutely massive
> > and so have a significant impact on the host OS in terms of time
> > & I/O bandwidth required to dump the guest, as well as disk space
> > usage. So core dumps are an opt-in thing.
> > 
> 
> I must've missed the place where we forbade it then.

QEMU will just inherit default limits from libvirtd, and libvirtd will
get a core file size of 0 from systemd unless you customize the systemd
unit file.

Regards,
Daniel
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