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>

1 files changed, 21 insertions, 0 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;
         }