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

[Jason Baron]

Add a new '[,dump=on|off]' option to the '-m' memory option. When 'dump=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 6 MB on a 2GB guest.
Thanks to Avi Kivity for the command line syntax.

Signed-off-by: Jason Baron <address@hidden>
---
 exec.c          |   13 +++++++++++++
 osdep.h         |    7 +++++++
 qemu-options.hx |   11 +++++++----
 sysemu.h        |    1 +
 vl.c            |   51 +++++++++++++++++++++++++++++++++++----------------
 5 files changed, 63 insertions(+), 20 deletions(-)

diff --git a/exec.c b/exec.c
index feb4795..75b8e23 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) {
+        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=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-options.hx b/qemu-options.hx
index dc68e15..9c21b99 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -382,14 +382,17 @@ the write back by pressing @key{C-a s} 
(@pxref{disk_images}).
 ETEXI
 
 DEF("m", HAS_ARG, QEMU_OPTION_m,
-    "-m megs         set virtual RAM size to megs MB [default="
-    stringify(DEFAULT_RAM_SIZE) "]\n", QEMU_ARCH_ALL)
+    "-m megs[,dump=on|off]\n"
+    "                set virtual RAM size to megs MB [default=" 
stringify(DEFAULT_RAM_SIZE) "]\n"
+    "                use 'dump=off' to omit guest memory from a core dump 
[default=on]\n",
+     QEMU_ARCH_ALL)
 STEXI
address@hidden -m @var{megs}
address@hidden -m @var{megs}[,dump=on|off]
 @findex -m
 Set virtual RAM size to @var{megs} megabytes. Default is 128 MiB.  Optionally,
 a suffix of ``M'' or ``G'' can be used to signify a value in megabytes or
-gigabytes respectively.
+gigabytes respectively. When 'dump=off' is specified, the guest memory is 
omitted
+from a qemu core dump. The default is 'dump=on'.
 ETEXI
 
 DEF("mem-path", HAS_ARG, QEMU_OPTION_mempath,
diff --git a/sysemu.h b/sysemu.h
index 6540c79..f1a6f08 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;
 
 #define MAX_NODES 64
 extern int nb_numa_nodes;
diff --git a/vl.c b/vl.c
index c18bb80..54ff314 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;
 
 typedef struct FWBootEntry FWBootEntry;
 
@@ -1041,6 +1042,38 @@ static void smp_parse(const char *optarg)
         max_cpus = smp_cpus;
 }
 
+static void memory_parse(const char *optarg)
+{
+    char option[128];
+    int64_t value;
+    char *end;
+
+    optarg = get_opt_name(option, 128, optarg, ',');
+    value = strtosz(option, &end);
+    if (value < 0 || (*end && (*end != ','))) {
+        fprintf(stderr, "qemu: invalid ram size: %s\n", option);
+        exit(1);
+    }
+    if (value != (uint64_t)(ram_addr_t)value) {
+        fprintf(stderr, "qemu: ram size too large\n");
+        exit(1);
+    }
+    ram_size = value;
+    if (*optarg == ',') {
+        optarg++;
+    }
+    if (get_param_value(option, 128, "dump", optarg) != 0) {
+        if (!strcmp(option, "on")) {
+            dont_dump_guest = 0;
+        } else if (!strcmp(option, "off")) {
+            dont_dump_guest = 1;
+        } else {
+            fprintf(stderr, "qemu: invalid option value '%s'\n", option);
+            exit(1);
+        }
+    }
+}
+
 /***********************************************************/
 /* USB devices */
 
@@ -2650,23 +2683,9 @@ int main(int argc, char **argv, char **envp)
                 version();
                 exit(0);
                 break;
-            case QEMU_OPTION_m: {
-                int64_t value;
-                char *end;
-
-                value = strtosz(optarg, &end);
-                if (value < 0 || *end) {
-                    fprintf(stderr, "qemu: invalid ram size: %s\n", optarg);
-                    exit(1);
-                }
-
-                if (value != (uint64_t)(ram_addr_t)value) {
-                    fprintf(stderr, "qemu: ram size too large\n");
-                    exit(1);
-                }
-                ram_size = value;
+            case QEMU_OPTION_m:
+                memory_parse(optarg);
                 break;
-            }
             case QEMU_OPTION_mempath:
                 mem_path = optarg;
                 break;
-- 
1.7.1