memory: add -machine dump-guest-core=on|off

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.

Is anything additional required to preserve this setting for migration or
savevm? I don't believe so.

Changelog:
v3:
    Eliminate globals as per Anthony's suggestion
    set no dump from qemu_ram_remap() as well
v2:
    move the option from -m to -machine, rename option dump -> dump-guest-core

Signed-off-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

4 files changed, 36 insertions, 1 deletions

diff --git a/exec.c b/exec.c
index 929db5c..5834766 100644
--- a/exec.c
+++ b/exec.c
@@ -2475,6 +2475,24 @@ static ram_addr_t last_ram_offset(void)
     return last;
 }
 
+static void qemu_ram_setup_dump(void *addr, ram_addr_t size)
+{
+    int ret;
+    QemuOpts *machine_opts;
+
+    /* Use MADV_DONTDUMP, if user doesn't want the guest memory in the core */
+    machine_opts = qemu_opts_find(qemu_find_opts("machine"), 0);
+    if (machine_opts &&
+        !qemu_opt_get_bool(machine_opts, "dump-guest-core", true)) {
+        ret = qemu_madvise(addr, size, QEMU_MADV_DONTDUMP);
+        if (ret) {
+            perror("qemu_madvise");
+            fprintf(stderr, "madvise doesn't support MADV_DONTDUMP, "
+                            "but dump_guest_core=off specified\n");
+        }
+    }
+}
+
 void qemu_ram_set_idstr(ram_addr_t addr, const char *name, DeviceState *dev)
 {
     RAMBlock *new_block, *block;
@@ -2554,6 +2572,8 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
            0, size >> TARGET_PAGE_BITS);
     cpu_physical_memory_set_dirty_range(new_block->offset, size, 0xff);
 
+    qemu_ram_setup_dump(new_block->host, size);
+
     if (kvm_enabled())
         kvm_setup_guest_memory(new_block->host, size);
 
@@ -2670,6 +2690,7 @@ void qemu_ram_remap(ram_addr_t addr, ram_addr_t length)
                     exit(1);
                 }
                 qemu_madvise(vaddr, length, QEMU_MADV_MERGEABLE);
+                qemu_ram_setup_dump(vaddr, length);
             }
             return;
         }
diff --git a/osdep.h b/osdep.h
index d4b887d..cb213e0 100644
--- a/osdep.h
+++ b/osdep.h
@@ -103,6 +103,11 @@ 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)
 
@@ -110,6 +115,7 @@ 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 */
 
@@ -117,6 +123,7 @@ 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..6700de0 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 47cb5bd..6aeef6a 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -37,7 +37,8 @@ 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}[,...]]
@@ -54,6 +55,8 @@ 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