[libvirt] [PATCH 1/2] qemu: add a max_core setting to qemu.conf for core dump size
Daniel P. Berrange
berrange at redhat.com
Tue Sep 6 11:20:42 UTC 2016
On Wed, Aug 17, 2016 at 05:04:48PM -0400, John Ferlan wrote:
>
>
> On 08/03/2016 11:31 AM, 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 controlled from qemu.conf instead.
> > ---
> > src/libvirt_private.syms | 2 ++
> > src/qemu/libvirtd_qemu.aug | 4 ++++
> > src/qemu/qemu.conf | 23 ++++++++++++++++++++++-
> > 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, 100 insertions(+), 1 deletion(-)
> >
> > diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
> > index 419c33d..6dc2b23 100644
> > --- a/src/libvirt_private.syms
> > +++ b/src/libvirt_private.syms
> > @@ -1389,6 +1389,7 @@ virCommandSetErrorFD;
> > virCommandSetGID;
> > virCommandSetInputBuffer;
> > virCommandSetInputFD;
> > +virCommandSetMaxCoreSize;
> > virCommandSetMaxFiles;
> > virCommandSetMaxMemLock;
> > virCommandSetMaxProcesses;
> > @@ -2199,6 +2200,7 @@ virProcessRunInMountNamespace;
> > virProcessSchedPolicyTypeFromString;
> > virProcessSchedPolicyTypeToString;
> > virProcessSetAffinity;
> > +virProcessSetMaxCoreSize;
> > virProcessSetMaxFiles;
> > virProcessSetMaxMemLock;
> > virProcessSetMaxProcesses;
> > diff --git a/src/qemu/libvirtd_qemu.aug b/src/qemu/libvirtd_qemu.aug
> > index 8bc23ba..9ec8250 100644
> > --- a/src/qemu/libvirtd_qemu.aug
> > +++ b/src/qemu/libvirtd_qemu.aug
> > @@ -22,6 +22,9 @@ module Libvirtd_qemu =
> > let int_entry (kw:string) = [ key kw . value_sep . int_val ]
> > let str_array_entry (kw:string) = [ key kw . value_sep . str_array_val ]
> >
> > + let unlimited_val = del /\"/ "\"" . store /unlimited/ . del /\"/ "\""
> > + let limits_entry (kw:string) = [ key kw . value_sep . unlimited_val ] | [ key kw . value_sep . int_val ]
> > +
>
> Is there no 'uulong_val'? At the very least uint? I don't know much
> about this aug stuff, so I defer to you on this.
There's no built-in types at all in augeas - we just define the grammar
entirely ourselves.
> > (* Config entry grouped by function - same order as example config *)
> > let vnc_entry = str_entry "vnc_listen"
> > @@ -72,6 +75,7 @@ module Libvirtd_qemu =
> > | bool_entry "set_process_name"
> > | int_entry "max_processes"
> > | int_entry "max_files"
> > + | limits_entry "max_core"
> > | str_entry "stdio_handler"
> >
> > let device_entry = bool_entry "mac_filter"
> > diff --git a/src/qemu/qemu.conf b/src/qemu/qemu.conf
> > index 7964273..abf9938 100644
> > --- a/src/qemu/qemu.conf
> > +++ b/src/qemu/qemu.conf
> > @@ -401,7 +401,28 @@
> > #max_processes = 0
> > #max_files = 0
> >
> > -
> > +# If max_core is set to a positive integer, then QEMU will be
> > +# permitted to create core dumps when it crashes, provided its
> > +# RAM size is smaller than the limit set.
>
> Providing a negative value will cause libvirtd startup failure... The
> way this is worded could lead one to believe they could provide a signed
> value.
Ok, i'll reword it.
> > +# Be warned that the core dump will include a full copy of the
> > +# guest RAM, unless it has been disabled via the guest XML by
> > +# setting:
> > +#
> > +# <memory dumpcore="off">...guest ram...</memory>
> > +#
> > +# If guest RAM is to be included, ensure the max_core limit
> > +# is set to at least the size of the largest expected guest
> > +# plus another 1GB for any QEMU host side memory mappings.
> > +#
> > +# As a special case it can be set to the string "unlimited" to
> > +# to allow arbitrarily sized core dumps.
> > +#
> > +# By default the core dump size is set to 0 disabling all dumps
> > +#
> > +# Size is in bytes or string "unlimited"
> > +#
> > +#max_core = "unlimited"
> >
>
> Would it be overly complicated to alter max_core to be "unlimited" or a
> sized value? I would think it would be easier to type/see "5G" rather
> than do the math! or fat-finger or cut-n-paste wrong...
Currently our config file format is essentially python variable
initialization syntax, so you can have unquoted numbers, or quoted
strings. So we could not have a bare 5G - it would have to be input
as a string which I think would be confusing - eg users would expect
these to work:
max_core = 5368709120
max_core = 5G
but would in fact have to use
max_core = 5368709120
max_core = "5G"
we could solve this by extending the virConf parsing code to deal
with bare sized values, but I don't fancy attacking that problem
right now.
> > @@ -1105,6 +1110,15 @@ virCommandSetMaxFiles(virCommandPtr cmd, unsigned int files)
> > cmd->maxFiles = files;
> > }
> >
> > +void virCommandSetMaxCoreSize(virCommandPtr cmd, unsigned long long bytes)
> > +{
> > + if (!cmd || cmd->has_error)
> > + return;
> > +
> > + cmd->maxCore = bytes;
>
> Should this check if bytes == 0 before setting to true? If not, then
> another change probably would be necessary below... [1]
Yep, we can check for 0.
> > diff --git a/src/util/virprocess.c b/src/util/virprocess.c
> > index 09dd3c9..2b71445 100644
> > --- a/src/util/virprocess.c
> > +++ b/src/util/virprocess.c
> > @@ -914,6 +914,42 @@ virProcessSetMaxFiles(pid_t pid ATTRIBUTE_UNUSED, unsigned int files)
> > }
> > #endif /* ! (HAVE_SETRLIMIT && defined(RLIMIT_NOFILE)) */
> >
> > +#if HAVE_SETRLIMIT && defined(RLIMIT_CORE)
> > +int
> > +virProcessSetMaxCoreSize(pid_t pid, unsigned long long bytes)
> > +{
> > + struct rlimit rlim;
> > +
> > + rlim.rlim_cur = rlim.rlim_max = bytes;
> > + if (pid == 0) {
> > + if (setrlimit(RLIMIT_CORE, &rlim) < 0) {
> > + virReportSystemError(errno,
> > + _("cannot limit core file size to %llu"),
> > + bytes);
> > + return -1;
> > + }
> > + } else {
> > + if (virProcessPrLimit(pid, RLIMIT_CORE, &rlim, NULL) < 0) {
> > + virReportSystemError(errno,
> > + _("cannot limit core file size "
> > + "of process %lld to %llu"),
> > + (long long int)pid, bytes);
> > + return -1;
> > + }
> > + }
> > + return 0;
> > +}
> > +#else /* ! (HAVE_SETRLIMIT && defined(RLIMIT_CORE)) */
> > +int
> > +virProcessSetMaxCoreSize(pid_t pid ATTRIBUTE_UNUSED,
> > + unsigned long long bytes ATTRIBUTE_UNUSED)
> > +{
>
> [1] Similar to other such functions should this have a :
>
> if (!bytes)
> return 0;
>
> and of course a removed ATTRIBUTE_UNUSED on bytes above...
Yep.
Regards,
Daniel
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