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

[Jason Baron]

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 <address@hidden>
---
 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) {
+        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",
+            .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 address@hidden,address@hidden,...]]
@@ -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.
address@hidden 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;
 
 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;
             case QEMU_OPTION_usb:
                 usb_enabled = 1;
-- 
1.7.1