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

[Anthony Liguori <anthony@codemonkey.ws>]

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")) {

> +        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"

> +            .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.

>  
>  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.

Regards,

Anthony Liguori

>              case QEMU_OPTION_usb:
>                  usb_enabled = 1;
> -- 
> 1.7.1