Re: [Qemu-devel] [PATCH v2] memory: add cmd line option, to omit guest memory from qemu core dump

[Jason Baron <jbaron@redhat.com>]

On Wed, Aug 01, 2012 at 01:21:57PM -0500, Anthony Liguori wrote:
> Jason Baron <jbaron@redhat.com> writes:
> 
> > Add a new '[,dump_guest_core=on|off]' option to the '-machine' option. When
> > 'dump_guest_core=off' is specified, guest memory is omitted from the core dump.
> > The default behavior continues to be to include guest memory when a core dump is
> > triggered. In my testing, this brought the core dump size down from 384MB to 6MB
> > on a 2GB guest.
> >
> > Changelog:
> > v2: move the option from -m to -machine, rename option dump -> dump_guest_core
> >
> > Signed-off-by: Jason Baron <jbaron@redhat.com>
> > ---
> >  exec.c          |   13 +++++++++++++
> >  osdep.h         |    7 +++++++
> >  qemu-config.c   |    4 ++++
> >  qemu-options.hx |    5 ++++-
> >  sysemu.h        |    1 +
> >  vl.c            |    4 ++++
> >  6 files changed, 33 insertions(+), 1 deletions(-)
> >
> > diff --git a/exec.c b/exec.c
> > index feb4795..0764818 100644
> > --- a/exec.c
> > +++ b/exec.c
> > @@ -35,6 +35,7 @@
> >  #include "qemu-timer.h"
> >  #include "memory.h"
> >  #include "exec-memory.h"
> > +#include "sysemu.h"
> >  #if defined(CONFIG_USER_ONLY)
> >  #include <qemu.h>
> >  #if defined(__FreeBSD__) || defined(__FreeBSD_kernel__)
> > @@ -2514,6 +2515,7 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
> >                                     MemoryRegion *mr)
> >  {
> >      RAMBlock *new_block;
> > +    int ret;
> >  
> >      size = TARGET_PAGE_ALIGN(size);
> >      new_block = g_malloc0(sizeof(*new_block));
> > @@ -2555,6 +2557,17 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
> >                                         last_ram_offset() >> TARGET_PAGE_BITS);
> >      cpu_physical_memory_set_dirty_range(new_block->offset, size, 0xff);
> >  
> > +
> > +    /* Use MADV_DONTDUMP, if user doesn't want the guest memory in the core */
> > +    if (dont_dump_guest_core) {
> 
>     machine_opts = qemu_opts_find(qemu_find_opts("machine"), 0);
>     if (machine_opts && qemu_opt_get_bool(machine_opts, "dump-guest-core")) {
> 

should be:
 
... && !qemu_opt_get_bool(machine_opts, "dump-guest-core", true)

??

> > +        ret = qemu_madvise(new_block->host, size, QEMU_MADV_DONTDUMP);
> > +        if (ret) {
> > +            perror("qemu_madvise");
> > +            fprintf(stderr, "madvise doesn't support MADV_DONTDUMP, "
> > +                            "but dump_guest_core=off specified\n");
> > +        }
> > +    }
> > +
> >      if (kvm_enabled())
> >          kvm_setup_guest_memory(new_block->host, size);
> >  
> > diff --git a/osdep.h b/osdep.h
> > index 1e15a4b..e2d0f57 100644
> > --- a/osdep.h
> > +++ b/osdep.h
> > @@ -102,6 +102,11 @@ void qemu_vfree(void *ptr);
> >  #else
> >  #define QEMU_MADV_MERGEABLE QEMU_MADV_INVALID
> >  #endif
> > +#ifdef MADV_DONTDUMP
> > +#define QEMU_MADV_DONTDUMP MADV_DONTDUMP
> > +#else
> > +#define QEMU_MADV_DONTDUMP QEMU_MADV_INVALID
> > +#endif
> >  
> >  #elif defined(CONFIG_POSIX_MADVISE)
> >  
> > @@ -109,6 +114,7 @@ void qemu_vfree(void *ptr);
> >  #define QEMU_MADV_DONTNEED  POSIX_MADV_DONTNEED
> >  #define QEMU_MADV_DONTFORK  QEMU_MADV_INVALID
> >  #define QEMU_MADV_MERGEABLE QEMU_MADV_INVALID
> > +#define QEMU_MADV_DONTDUMP QEMU_MADV_INVALID
> >  
> >  #else /* no-op */
> >  
> > @@ -116,6 +122,7 @@ void qemu_vfree(void *ptr);
> >  #define QEMU_MADV_DONTNEED  QEMU_MADV_INVALID
> >  #define QEMU_MADV_DONTFORK  QEMU_MADV_INVALID
> >  #define QEMU_MADV_MERGEABLE QEMU_MADV_INVALID
> > +#define QEMU_MADV_DONTDUMP QEMU_MADV_INVALID
> >  
> >  #endif
> >  
> > diff --git a/qemu-config.c b/qemu-config.c
> > index 5c3296b..5c2c9a9 100644
> > --- a/qemu-config.c
> > +++ b/qemu-config.c
> > @@ -595,6 +595,10 @@ static QemuOptsList qemu_machine_opts = {
> >              .name = "dt_compatible",
> >              .type = QEMU_OPT_STRING,
> >              .help = "Overrides the \"compatible\" property of the dt root node",
> > +        }, {
> > +            .name = "dump_guest_core",
> 
> "dump-guest-core"
> 

ok.

> > +            .type = QEMU_OPT_BOOL,
> > +            .help = "Include guest memory in  a core dump",
> >          },
> >          { /* End of list */ }
> >      },
> > diff --git a/qemu-options.hx b/qemu-options.hx
> > index dc68e15..e917829 100644
> > --- a/qemu-options.hx
> > +++ b/qemu-options.hx
> > @@ -33,7 +33,8 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \
> >      "                property accel=accel1[:accel2[:...]] selects accelerator\n"
> >      "                supported accelerators are kvm, xen, tcg (default: tcg)\n"
> >      "                kernel_irqchip=on|off controls accelerated irqchip support\n"
> > -    "                kvm_shadow_mem=size of KVM shadow MMU\n",
> > +    "                kvm_shadow_mem=size of KVM shadow MMU\n"
> > +    "                dump_guest_core=on|off include guest memory in a core dump (default=on)\n",
> >      QEMU_ARCH_ALL)
> >  STEXI
> >  @item -machine [type=]@var{name}[,prop=@var{value}[,...]]
> > @@ -50,6 +51,8 @@ to initialize.
> >  Enables in-kernel irqchip support for the chosen accelerator when available.
> >  @item kvm_shadow_mem=size
> >  Defines the size of the KVM shadow MMU.
> > +@item dump_guest_core=on|off
> > +Include guest memory in a core dump. The default is on.
> >  @end table
> >  ETEXI
> >  
> > diff --git a/sysemu.h b/sysemu.h
> > index 6540c79..caf33ce 100644
> > --- a/sysemu.h
> > +++ b/sysemu.h
> > @@ -132,6 +132,7 @@ extern uint8_t *boot_splash_filedata;
> >  extern int boot_splash_filedata_size;
> >  extern uint8_t qemu_extra_params_fw[2];
> >  extern QEMUClock *rtc_clock;
> > +extern int dont_dump_guest_core;
> >  
> >  #define MAX_NODES 64
> >  extern int nb_numa_nodes;
> > diff --git a/vl.c b/vl.c
> > index c18bb80..accfd28 100644
> > --- a/vl.c
> > +++ b/vl.c
> > @@ -226,6 +226,7 @@ int boot_menu;
> >  uint8_t *boot_splash_filedata;
> >  int boot_splash_filedata_size;
> >  uint8_t qemu_extra_params_fw[2];
> > +int dont_dump_guest_core;
> 
> Drop the globals.
> 

ok.

> >  
> >  typedef struct FWBootEntry FWBootEntry;
> >  
> > @@ -2976,6 +2977,9 @@ int main(int argc, char **argv, char **envp)
> >                  if (optarg) {
> >                      machine = machine_parse(optarg);
> >                  }
> > +                if (!qemu_opt_get_bool(opts, "dump_guest_core", true)) {
> > +                    dont_dump_guest_core = 1;
> > +                }
> >                  break;
> 
> The -machine option is not the only way to set machine options so this
> is incorrect.  But if you do what I suggest above, you can just drop
> this whole bit and not worry about it.
> 

ok. oops.

Thanks,

-Jason