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Re: [libvirt] [PATCH] Raise default limit on number of processes for qemu user



On Wed, Mar 09, 2011 at 02:20:09PM +0100, Jiri Denemark wrote:
> The daemon/libvirtd.limits file (which is supposed to be copied to
> /etc/security/limits.d/libvirtd.conf) is generated based on --qemu-user
> option passed at configure time.
> 
> The file is intentionally not installed by make install since installing
> it on distributions with higher or no limit on number of process could
> actually result in lowering the limit. Packagers may choose whether to
> install the file or not. It is installed by libvirt.spec for RPM based
> distributions.
> ---
>  configure.ac              |    3 ++-
>  daemon/libvirtd.limits.in |    6 ++++++
>  libvirt.spec.in           |    7 +++++++
>  src/qemu/qemu.conf        |    4 +++-
>  4 files changed, 18 insertions(+), 2 deletions(-)
>  create mode 100644 daemon/libvirtd.limits.in
> 
> diff --git a/configure.ac b/configure.ac
> index a58ee4e..d8002b4 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -2237,6 +2237,7 @@ AC_ARG_WITH([qemu-group],
>    [QEMU_GROUP=root])
>  AC_DEFINE_UNQUOTED([QEMU_USER], ["$QEMU_USER"], [QEMU user account])
>  AC_DEFINE_UNQUOTED([QEMU_GROUP], ["$QEMU_GROUP"], [QEMU group account])
> +AC_SUBST([QEMU_USER])
>  
>  
>  AC_ARG_WITH([macvtap],
> @@ -2344,7 +2345,7 @@ AC_OUTPUT(Makefile src/Makefile include/Makefile docs/Makefile \
>            po/Makefile.in \
>  	  include/libvirt/Makefile include/libvirt/libvirt.h \
>  	  python/Makefile python/tests/Makefile \
> -          daemon/Makefile \
> +          daemon/Makefile daemon/libvirtd.limits \
>            tools/Makefile \
>            tests/Makefile \
>            examples/apparmor/Makefile \
> diff --git a/daemon/libvirtd.limits.in b/daemon/libvirtd.limits.in
> new file mode 100644
> index 0000000..7b580ae
> --- /dev/null
> +++ b/daemon/libvirtd.limits.in
> @@ -0,0 +1,6 @@
> +# /etc/security/limits.d/libvirtd.conf
> +#
> +# Increase default limit for number of processes owned by qemu-user
> +# Also see @sysconfdir@/libvirt/qemu.conf where qemu-user can be overridden
> +
> + QEMU_USER@	soft	nproc	10000
> diff --git a/libvirt.spec.in b/libvirt.spec.in
> index 45a8fe0..02be928 100644
> --- a/libvirt.spec.in
> +++ b/libvirt.spec.in
> @@ -705,6 +705,12 @@ mv $RPM_BUILD_ROOT%{_datadir}/doc/libvirt-%{version}/html \
>  rm -rf $RPM_BUILD_ROOT%{_sysconfdir}/libvirt/qemu.conf
>  rm -rf $RPM_BUILD_ROOT%{_sysconfdir}/logrotate.d/libvirtd.qemu
>  %endif
> +
> +%if %{with_libvirtd} && %{with_qemu}
> +install -d -m 0755 $RPM_BUILD_ROOT%{_sysconfdir}/security/limits.d/
> +cp daemon/libvirtd.limits \
> +   $RPM_BUILD_ROOT%{_sysconfdir}/security/limits.d/libvirtd.conf
> +%endif
>  %if ! %{with_lxc}
>  rm -rf $RPM_BUILD_ROOT%{_sysconfdir}/libvirt/lxc.conf
>  rm -rf $RPM_BUILD_ROOT%{_sysconfdir}/logrotate.d/libvirtd.lxc
> @@ -869,6 +875,7 @@ fi
>  %if %{with_qemu}
>  %config(noreplace) %{_sysconfdir}/libvirt/qemu.conf
>  %config(noreplace) %{_sysconfdir}/logrotate.d/libvirtd.qemu
> +%config(noreplace) %{_sysconfdir}/security/limits.d/libvirtd.conf
>  %endif
>  %if %{with_lxc}
>  %config(noreplace) %{_sysconfdir}/libvirt/lxc.conf
> diff --git a/src/qemu/qemu.conf b/src/qemu/qemu.conf
> index 8c6b996..52c6ac7 100644
> --- a/src/qemu/qemu.conf
> +++ b/src/qemu/qemu.conf
> @@ -139,7 +139,9 @@
>  # security_driver = "selinux"
>  
>  
> -# The user ID for QEMU processes run by the system instance.
> +# The user ID for QEMU processes run by the system instance. If you
> +# change this setting, /etc/security/limits.d/libvirtd.conf (if
> +# installed) needs to be changed to match this user ID.
>  #user = "root"

Hmm, did you actually test this setup to make sure it works as we
expect ?  I have this nasty feeling in the back of my mind that
the files under /etc/security/limits.d/ are only processed by
PAM modules. Since PAM isn't at all involved when libvirt changes
UID to 'qemu' to launch QEMU, how does QEMU actually see the increased
limit being set ?

Something needs to be calling the setrlimit() systemcall for the
QEMU process when it is launched and I don't see what is yet ?

Daniel
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