[Qemu-devel] [RFC][PATCH 09/15] introduce a new monitor command 'dump' to dump guest's memory

[Wen Congyang <wency@cn.fujitsu.com>]

Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
---
 Makefile.target  |    8 +-
 dump.c           |  590 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 dump.h           |    3 +
 hmp-commands.hx  |   16 ++
 hmp.c            |    9 +
 hmp.h            |    1 +
 monitor.c        |    3 +
 qapi-schema.json |   13 ++
 qmp-commands.hx  |   26 +++
 9 files changed, 665 insertions(+), 4 deletions(-)
 create mode 100644 dump.c

diff --git a/Makefile.target b/Makefile.target
index d869550..abfb057 100644
--- a/Makefile.target
+++ b/Makefile.target
@@ -110,7 +110,7 @@ $(call set-vpath, $(SRC_PATH)/linux-user:$(SRC_PATH)/linux-user/$(TARGET_ABI_DIR
 QEMU_CFLAGS+=-I$(SRC_PATH)/linux-user/$(TARGET_ABI_DIR) -I$(SRC_PATH)/linux-user
 obj-y = main.o syscall.o strace.o mmap.o signal.o thunk.o \
       elfload.o linuxload.o uaccess.o gdbstub.o cpu-uname.o \
-      user-exec.o $(oslib-obj-y)
+      user-exec.o $(oslib-obj-y) dump.o
 
 obj-$(TARGET_HAS_BFLT) += flatload.o
 
@@ -148,7 +148,7 @@ LDFLAGS+=-Wl,-segaddr,__STD_PROG_ZONE,0x1000 -image_base 0x0e000000
 LIBS+=-lmx
 
 obj-y = main.o commpage.o machload.o mmap.o signal.o syscall.o thunk.o \
-        gdbstub.o user-exec.o
+        gdbstub.o user-exec.o dump.o
 
 obj-i386-y += ioport-user.o
 
@@ -170,7 +170,7 @@ $(call set-vpath, $(SRC_PATH)/bsd-user)
 QEMU_CFLAGS+=-I$(SRC_PATH)/bsd-user -I$(SRC_PATH)/bsd-user/$(TARGET_ARCH)
 
 obj-y = main.o bsdload.o elfload.o mmap.o signal.o strace.o syscall.o \
-        gdbstub.o uaccess.o user-exec.o
+        gdbstub.o uaccess.o user-exec.o dump.o
 
 obj-i386-y += ioport-user.o
 
@@ -186,7 +186,7 @@ endif #CONFIG_BSD_USER
 # System emulator target
 ifdef CONFIG_SOFTMMU
 
-obj-y = arch_init.o cpus.o monitor.o machine.o gdbstub.o balloon.o ioport.o
+obj-y = arch_init.o cpus.o monitor.o machine.o gdbstub.o balloon.o ioport.o dump.o
 # virtio has to be here due to weird dependency between PCI and virtio-net.
 # need to fix this properly
 obj-$(CONFIG_NO_PCI) += pci-stub.o
diff --git a/dump.c b/dump.c
new file mode 100644
index 0000000..2951b8b
--- /dev/null
+++ b/dump.c
@@ -0,0 +1,590 @@
+/*
+ * QEMU dump
+ *
+ * Copyright Fujitsu, Corp. 2011
+ *
+ * Authors:
+ *     Wen Congyang <wency@cn.fujitsu.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+#include "qemu-common.h"
+#include <unistd.h>
+#include <elf.h>
+#include <sys/procfs.h>
+#include <glib.h>
+#include "cpu.h"
+#include "cpu-all.h"
+#include "targphys.h"
+#include "monitor.h"
+#include "kvm.h"
+#include "dump.h"
+#include "sysemu.h"
+#include "bswap.h"
+#include "memory_mapping.h"
+#include "error.h"
+#include "qmp-commands.h"
+
+#define CPU_CONVERT_TO_TARGET16(val) \
+({ \
+    uint16_t _val = (val); \
+    if (endian == ELFDATA2LSB) { \
+        _val = cpu_to_le16(_val); \
+    } else {\
+        _val = cpu_to_be16(_val); \
+    } \
+    _val; \
+})
+
+#define CPU_CONVERT_TO_TARGET32(val) \
+({ \
+    uint32_t _val = (val); \
+    if (endian == ELFDATA2LSB) { \
+        _val = cpu_to_le32(_val); \
+    } else {\
+        _val = cpu_to_be32(_val); \
+    } \
+    _val; \
+})
+
+#define CPU_CONVERT_TO_TARGET64(val) \
+({ \
+    uint64_t _val = (val); \
+    if (endian == ELFDATA2LSB) { \
+        _val = cpu_to_le64(_val); \
+    } else {\
+        _val = cpu_to_be64(_val); \
+    } \
+    _val; \
+})
+
+enum {
+    DUMP_STATE_ERROR,
+    DUMP_STATE_SETUP,
+    DUMP_STATE_CANCELLED,
+    DUMP_STATE_ACTIVE,
+    DUMP_STATE_COMPLETED,
+};
+
+typedef struct DumpState {
+    ArchDumpInfo dump_info;
+    MemoryMappingList list;
+    int phdr_num;
+    int state;
+    char *error;
+    int fd;
+    target_phys_addr_t memory_offset;
+} DumpState;
+
+static DumpState *dump_get_current(void)
+{
+    static DumpState current_dump = {
+        .state = DUMP_STATE_SETUP,
+    };
+
+    return &current_dump;
+}
+
+static int dump_cleanup(DumpState *s)
+{
+    int ret = 0;
+
+    free_memory_mapping_list(&s->list);
+    if (s->fd != -1) {
+        close(s->fd);
+        s->fd = -1;
+    }
+
+    return ret;
+}
+
+static void dump_error(DumpState *s, const char *reason)
+{
+    s->state = DUMP_STATE_ERROR;
+    s->error = g_strdup(reason);
+    dump_cleanup(s);
+}
+
+static inline int cpuid(CPUState *env)
+{
+#if defined(CONFIG_USER_ONLY) && defined(CONFIG_USE_NPTL)
+    return env->host_tid;
+#else
+    return env->cpu_index + 1;
+#endif
+}
+
+static int write_elf64_header(DumpState *s)
+{
+    Elf64_Ehdr elf_header;
+    int ret;
+    int endian = s->dump_info.d_endian;
+
+    memset(&elf_header, 0, sizeof(Elf64_Ehdr));
+    memcpy(&elf_header, ELFMAG, 4);
+    elf_header.e_ident[EI_CLASS] = ELFCLASS64;
+    elf_header.e_ident[EI_DATA] = s->dump_info.d_endian;
+    elf_header.e_ident[EI_VERSION] = EV_CURRENT;
+    elf_header.e_type = CPU_CONVERT_TO_TARGET16(ET_CORE);
+    elf_header.e_machine = CPU_CONVERT_TO_TARGET16(s->dump_info.d_machine);
+    elf_header.e_version = CPU_CONVERT_TO_TARGET32(EV_CURRENT);
+    elf_header.e_ehsize = CPU_CONVERT_TO_TARGET16(sizeof(elf_header));
+    elf_header.e_phoff = CPU_CONVERT_TO_TARGET64(sizeof(Elf64_Ehdr));
+    elf_header.e_phentsize = CPU_CONVERT_TO_TARGET16(sizeof(Elf64_Phdr));
+    elf_header.e_phnum = CPU_CONVERT_TO_TARGET16(s->phdr_num);
+
+    lseek(s->fd, 0, SEEK_SET);
+    ret = write(s->fd, &elf_header, sizeof(elf_header));
+    if (ret < 0) {
+        dump_error(s, "dump: failed to write elf header.\n");
+        return -1;
+    }
+
+    return 0;
+}
+
+static int write_elf32_header(DumpState *s)
+{
+    Elf32_Ehdr elf_header;
+    int ret;
+    int endian = s->dump_info.d_endian;
+
+    memset(&elf_header, 0, sizeof(Elf32_Ehdr));
+    memcpy(&elf_header, ELFMAG, 4);
+    elf_header.e_ident[EI_CLASS] = ELFCLASS32;
+    elf_header.e_ident[EI_DATA] = endian;
+    elf_header.e_ident[EI_VERSION] = EV_CURRENT;
+    elf_header.e_type = CPU_CONVERT_TO_TARGET16(ET_CORE);
+    elf_header.e_machine = CPU_CONVERT_TO_TARGET16(s->dump_info.d_machine);
+    elf_header.e_version = CPU_CONVERT_TO_TARGET32(EV_CURRENT);
+    elf_header.e_ehsize = CPU_CONVERT_TO_TARGET16(sizeof(elf_header));
+    elf_header.e_phoff = CPU_CONVERT_TO_TARGET32(sizeof(Elf32_Ehdr));
+    elf_header.e_phentsize = CPU_CONVERT_TO_TARGET16(sizeof(Elf32_Phdr));
+    elf_header.e_phnum = CPU_CONVERT_TO_TARGET16(s->phdr_num);
+
+    lseek(s->fd, 0, SEEK_SET);
+    ret = write(s->fd, &elf_header, sizeof(elf_header));
+    if (ret < 0) {
+        dump_error(s, "dump: failed to write elf header.\n");
+        return -1;
+    }
+
+    return 0;
+}
+
+static int write_elf64_load(DumpState *s, MemoryMapping *memory_mapping,
+                            int phdr_index, target_phys_addr_t offset)
+{
+    Elf64_Phdr phdr;
+    off_t phdr_offset;
+    int ret;
+    int endian = s->dump_info.d_endian;
+
+    memset(&phdr, 0, sizeof(Elf64_Phdr));
+    phdr.p_type = CPU_CONVERT_TO_TARGET32(PT_LOAD);
+    phdr.p_offset = CPU_CONVERT_TO_TARGET64(offset);
+    phdr.p_paddr = CPU_CONVERT_TO_TARGET64(memory_mapping->phys_addr);
+    if (offset == -1) {
+        phdr.p_filesz = 0;
+    } else {
+        phdr.p_filesz = CPU_CONVERT_TO_TARGET64(memory_mapping->length);
+    }
+    phdr.p_memsz = CPU_CONVERT_TO_TARGET64(memory_mapping->length);
+    phdr.p_vaddr = CPU_CONVERT_TO_TARGET64(memory_mapping->virt_addr);
+
+    phdr_offset = sizeof(Elf64_Ehdr) + sizeof(Elf64_Phdr)*phdr_index;
+    lseek(s->fd, phdr_offset, SEEK_SET);
+    ret = write(s->fd, &phdr, sizeof(Elf64_Phdr));
+    if (ret < 0) {
+        dump_error(s, "dump: failed to write program header table.\n");
+        return -1;
+    }
+
+    return 0;
+}
+
+static int write_elf32_load(DumpState *s, MemoryMapping *memory_mapping,
+                            int phdr_index, target_phys_addr_t offset)
+{
+    Elf32_Phdr phdr;
+    off_t phdr_offset;
+    int ret;
+    int endian = s->dump_info.d_endian;
+
+    memset(&phdr, 0, sizeof(Elf32_Phdr));
+    phdr.p_type = CPU_CONVERT_TO_TARGET32(PT_LOAD);
+    phdr.p_offset = CPU_CONVERT_TO_TARGET32(offset);
+    phdr.p_paddr = CPU_CONVERT_TO_TARGET32(memory_mapping->phys_addr);
+    if (offset == -1) {
+        phdr.p_filesz = 0;
+    } else {
+        phdr.p_filesz = CPU_CONVERT_TO_TARGET32(memory_mapping->length);
+    }
+    phdr.p_memsz = CPU_CONVERT_TO_TARGET32(memory_mapping->length);
+    phdr.p_vaddr = CPU_CONVERT_TO_TARGET32(memory_mapping->virt_addr);
+
+    phdr_offset = sizeof(Elf32_Ehdr) + sizeof(Elf32_Phdr)*phdr_index;
+    lseek(s->fd, phdr_offset, SEEK_SET);
+    ret = write(s->fd, &phdr, sizeof(Elf32_Phdr));
+    if (ret < 0) {
+        dump_error(s, "dump: failed to write program header table.\n");
+        return -1;
+    }
+
+    return 0;
+}
+
+static int write_elf64_notes(DumpState *s, int phdr_index,
+                             target_phys_addr_t *offset)
+{
+    CPUState *env;
+    int ret;
+    target_phys_addr_t begin = *offset;
+    Elf64_Phdr phdr;
+    off_t phdr_offset;
+    int id;
+    int endian = s->dump_info.d_endian;
+
+    for (env = first_cpu; env != NULL; env = env->next_cpu) {
+        id = cpuid(env);
+        ret = cpu_write_elf64_note(s->fd, env, id, offset);
+        if (ret < 0) {
+            dump_error(s, "dump: failed to write elf notes.\n");
+            return -1;
+        }
+    }
+
+    memset(&phdr, 0, sizeof(Elf64_Phdr));
+    phdr.p_type = CPU_CONVERT_TO_TARGET32(PT_NOTE);
+    phdr.p_offset = CPU_CONVERT_TO_TARGET64(begin);
+    phdr.p_paddr = 0;
+    phdr.p_filesz = CPU_CONVERT_TO_TARGET64(*offset - begin);
+    phdr.p_memsz = CPU_CONVERT_TO_TARGET64(*offset - begin);
+    phdr.p_vaddr = 0;
+
+    phdr_offset = sizeof(Elf64_Ehdr);
+    lseek(s->fd, phdr_offset, SEEK_SET);
+    ret = write(s->fd, &phdr, sizeof(Elf64_Phdr));
+    if (ret < 0) {
+        dump_error(s, "dump: failed to write program header table.\n");
+        return -1;
+    }
+
+    return 0;
+}
+
+static int write_elf32_notes(DumpState *s, int phdr_index,
+                             target_phys_addr_t *offset)
+{
+    CPUState *env;
+    int ret;
+    target_phys_addr_t begin = *offset;
+    Elf32_Phdr phdr;
+    off_t phdr_offset;
+    int id;
+    int endian = s->dump_info.d_endian;
+
+    for (env = first_cpu; env != NULL; env = env->next_cpu) {
+        id = cpuid(env);
+        ret = cpu_write_elf32_note(s->fd, env, id, offset);
+        if (ret < 0) {
+            dump_error(s, "dump: failed to write elf notes.\n");
+            return -1;
+        }
+    }
+
+    memset(&phdr, 0, sizeof(Elf32_Phdr));
+    phdr.p_type = CPU_CONVERT_TO_TARGET32(PT_NOTE);
+    phdr.p_offset = CPU_CONVERT_TO_TARGET32(begin);
+    phdr.p_paddr = 0;
+    phdr.p_filesz = CPU_CONVERT_TO_TARGET32(*offset - begin);
+    phdr.p_memsz = CPU_CONVERT_TO_TARGET32(*offset - begin);
+    phdr.p_vaddr = 0;
+
+    phdr_offset = sizeof(Elf32_Ehdr);
+    lseek(s->fd, phdr_offset, SEEK_SET);
+    ret = write(s->fd, &phdr, sizeof(Elf32_Phdr));
+    if (ret < 0) {
+        dump_error(s, "dump: failed to write program header table.\n");
+        return -1;
+    }
+
+    return 0;
+}
+
+static int write_data(DumpState *s, void *buf, int length,
+                      target_phys_addr_t *offset)
+{
+    int ret;
+
+    lseek(s->fd, *offset, SEEK_SET);
+    ret = write(s->fd, buf, length);
+    if (ret < 0) {
+        dump_error(s, "dump: failed to save memory.\n");
+        return -1;
+    }
+
+    *offset += length;
+    return 0;
+}
+
+/* write the memroy to vmcore. 1 page per I/O. */
+static int write_memory(DumpState *s, RAMBlock *block,
+                        target_phys_addr_t *offset)
+{
+    int i, ret;
+
+    for (i = 0; i < block->length / TARGET_PAGE_SIZE; i++) {
+        ret = write_data(s, block->host + i * TARGET_PAGE_SIZE,
+                         TARGET_PAGE_SIZE, offset);
+        if (ret < 0) {
+            return -1;
+        }
+    }
+
+    if ((block->length % TARGET_PAGE_SIZE) != 0) {
+        ret = write_data(s, block->host + i * TARGET_PAGE_SIZE,
+                         block->length % TARGET_PAGE_SIZE, offset);
+        if (ret < 0) {
+            return -1;
+        }
+    }
+
+    return 0;
+}
+
+/* get the memory's offset in the vmcore */
+static target_phys_addr_t get_offset(target_phys_addr_t phys_addr,
+                                     target_phys_addr_t memory_offset)
+{
+    RAMBlock *block;
+    target_phys_addr_t offset = memory_offset;
+
+    QLIST_FOREACH(block, &ram_list.blocks, next) {
+        if (phys_addr >= block->offset &&
+            phys_addr < block->offset + block->length) {
+            return phys_addr - block->offset + offset;
+        }
+        offset += block->length;
+    }
+
+    return -1;
+}
+
+static DumpState *dump_init(int fd, Error **errp)
+{
+    CPUState *env;
+    DumpState *s = dump_get_current();
+    int ret;
+
+    vm_stop(RUN_STATE_PAUSED);
+    s->state = DUMP_STATE_SETUP;
+    if (s->error) {
+        g_free(s->error);
+        s->error = NULL;
+    }
+    s->fd = fd;
+
+    /*
+     * get dump info: endian, class and architecture.
+     * If the target architecture is not supported, cpu_get_dump_info() will
+     * return -1.
+     *
+     * if we use kvm, we should synchronize the register before we get dump
+     * info.
+     */
+    for (env = first_cpu; env != NULL; env = env->next_cpu) {
+        cpu_synchronize_state(env);
+    }
+    ret = cpu_get_dump_info(&s->dump_info);
+    if (ret < 0) {
+        error_set(errp, QERR_UNSUPPORTED);
+        return NULL;
+    }
+
+    /* get memory mapping */
+    s->list.num = 0;
+    QTAILQ_INIT(&s->list.head);
+    get_memory_mapping(&s->list);
+
+    /* crash needs extra memory mapping to determine phys_base. */
+    ret = cpu_add_extra_memory_mapping(&s->list);
+    if (ret < 0) {
+        error_set(errp, QERR_UNDEFINED_ERROR);
+        return NULL;
+    }
+
+    /*
+     * calculate phdr_num
+     *
+     * the type of phdr->num is uint16_t, so we should avoid overflow
+     */
+    s->phdr_num = 1; /* PT_NOTE */
+    if (s->list.num > (1 << 16) - 2) {
+        s->phdr_num = (1 << 16) - 1;
+    } else {
+        s->phdr_num += s->list.num;
+    }
+
+    return s;
+}
+
+/* write elf header, PT_NOTE and elf note to vmcore. */
+static int dump_begin(DumpState *s)
+{
+    target_phys_addr_t offset;
+    int ret;
+
+    s->state = DUMP_STATE_ACTIVE;
+
+    /*
+     * the vmcore's format is:
+     *   --------------
+     *   |  elf header |
+     *   --------------
+     *   |  PT_NOTE    |
+     *   --------------
+     *   |  PT_LOAD    |
+     *   --------------
+     *   |  ......     |
+     *   --------------
+     *   |  PT_LOAD    |
+     *   --------------
+     *   |  elf note   |
+     *   --------------
+     *   |  memory     |
+     *   --------------
+     *
+     * we only know where the memory is saved after we write elf note into
+     * vmcore.
+     */
+
+    /* write elf header to vmcore */
+    if (s->dump_info.d_class == ELFCLASS64) {
+        ret = write_elf64_header(s);
+    } else {
+        ret = write_elf32_header(s);
+    }
+    if (ret < 0) {
+        return -1;
+    }
+
+    /* write elf notes to vmcore */
+    if (s->dump_info.d_class == ELFCLASS64) {
+        offset = sizeof(Elf64_Ehdr) + sizeof(Elf64_Phdr)*s->phdr_num;
+        ret = write_elf64_notes(s, 0, &offset);
+    } else {
+        offset = sizeof(Elf32_Ehdr) + sizeof(Elf32_Phdr)*s->phdr_num;
+        ret = write_elf32_notes(s, 0, &offset);
+    }
+
+    if (ret < 0) {
+        return -1;
+    }
+
+    s->memory_offset = offset;
+    return 0;
+}
+
+/* write PT_LOAD to vmcore */
+static int dump_completed(DumpState *s)
+{
+    target_phys_addr_t offset;
+    MemoryMapping *memory_mapping;
+    int phdr_index = 1, ret;
+
+    QTAILQ_FOREACH(memory_mapping, &s->list.head, next) {
+        offset = get_offset(memory_mapping->phys_addr, s->memory_offset);
+        if (s->dump_info.d_class == ELFCLASS64) {
+            ret = write_elf64_load(s, memory_mapping, phdr_index++, offset);
+        } else {
+            ret = write_elf32_load(s, memory_mapping, phdr_index++, offset);
+        }
+        if (ret < 0) {
+            return -1;
+        }
+    }
+
+    s->state = DUMP_STATE_COMPLETED;
+    dump_cleanup(s);
+    return 0;
+}
+
+/* write all memory to vmcore */
+static int dump_iterate(DumpState *s)
+{
+    RAMBlock *block;
+    target_phys_addr_t offset = s->memory_offset;
+    int ret;
+
+    /* write all memory to vmcore */
+    QLIST_FOREACH(block, &ram_list.blocks, next) {
+        ret = write_memory(s, block, &offset);
+        if (ret < 0) {
+            return -1;
+        }
+    }
+
+    return dump_completed(s);
+}
+
+static int create_vmcore(DumpState *s)
+{
+    int ret;
+
+    ret = dump_begin(s);
+    if (ret < 0) {
+        return -1;
+    }
+
+    ret = dump_iterate(s);
+    if (ret < 0) {
+        return -1;
+    }
+
+    return 0;
+}
+
+void qmp_dump(const char *file, Error **errp)
+{
+    const char *p;
+    int fd = -1;
+    DumpState *s;
+
+#if !defined(WIN32)
+    if (strstart(file, "fd:", &p)) {
+        fd = qemu_get_fd(p);
+        if (fd == -1) {
+            error_set(errp, QERR_FD_NOT_FOUND, p);
+            return;
+        }
+    }
+#endif
+
+    if  (strstart(file, "file:", &p)) {
+        fd = open(p, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY);
+        if (fd < 0) {
+            error_set(errp, QERR_OPEN_FILE_FAILED, p);
+            return;
+        }
+    }
+
+    if (fd == -1) {
+        error_set(errp, QERR_INVALID_PARAMETER, "file");
+        return;
+    }
+
+    s = dump_init(fd, errp);
+    if (!s) {
+        return;
+    }
+
+    if (create_vmcore(s) < 0) {
+        error_set(errp, QERR_IO_ERROR);
+    }
+
+    return;
+}
diff --git a/dump.h b/dump.h
index a36468b..b413d18 100644
--- a/dump.h
+++ b/dump.h
@@ -1,6 +1,9 @@
 #ifndef DUMP_H
 #define DUMP_H
 
+#include "qdict.h"
+#include "error.h"
+
 typedef struct ArchDumpInfo {
     int d_machine;  /* Architecture */
     int d_endian;   /* ELFDATA2LSB or ELFDATA2MSB */
diff --git a/hmp-commands.hx b/hmp-commands.hx
index a586498..c3615e3 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -828,6 +828,22 @@ new parameters (if specified) once the vm migration finished successfully.
 ETEXI
 
     {
+        .name       = "dump",
+        .args_type  = "file:s",
+        .params     = "file",
+        .help       = "dump to file",
+        .user_print = monitor_user_noop,
+        .mhandler.cmd = hmp_dump,
+    },
+
+
+STEXI
+@item dump @var{file}
+@findex dump
+Dump to @var{file}.
+ETEXI
+
+    {
         .name       = "snapshot_blkdev",
         .args_type  = "device:B,snapshot-file:s?,format:s?",
         .params     = "device [new-image-file] [format]",
diff --git a/hmp.c b/hmp.c
index 8a77780..11b4ce6 100644
--- a/hmp.c
+++ b/hmp.c
@@ -681,3 +681,12 @@ void hmp_migrate_set_speed(Monitor *mon, const QDict *qdict)
     int64_t value = qdict_get_int(qdict, "value");
     qmp_migrate_set_speed(value, NULL);
 }
+
+void hmp_dump(Monitor *mon, const QDict *qdict)
+{
+    Error *errp = NULL;
+    const char *file = qdict_get_str(qdict, "file");
+
+    qmp_dump(file, &errp);
+    hmp_handle_error(mon, &errp);
+}
diff --git a/hmp.h b/hmp.h
index 093242d..8d6a5d2 100644
--- a/hmp.h
+++ b/hmp.h
@@ -49,5 +49,6 @@ void hmp_snapshot_blkdev(Monitor *mon, const QDict *qdict);
 void hmp_migrate_cancel(Monitor *mon, const QDict *qdict);
 void hmp_migrate_set_downtime(Monitor *mon, const QDict *qdict);
 void hmp_migrate_set_speed(Monitor *mon, const QDict *qdict);
+void hmp_dump(Monitor *mon, const QDict *qdict);
 
 #endif
diff --git a/monitor.c b/monitor.c
index ce2bc13..24d4371 100644
--- a/monitor.c
+++ b/monitor.c
@@ -73,6 +73,9 @@
 #endif
 #include "hw/lm32_pic.h"
 
+/* for dump */
+#include "dump.h"
+
 //#define DEBUG
 //#define DEBUG_COMPLETION
 
diff --git a/qapi-schema.json b/qapi-schema.json
index 44cf764..84c2c9a 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -1275,3 +1275,16 @@
 { 'command': 'qom-set',
   'data': { 'path': 'str', 'property': 'str', 'value': 'visitor' },
   'gen': 'no' }
+
+##
+# @dump
+#
+# Dump guest's memory to vmcore.
+#
+# @file: the filename or file descriptor of the vmcore.
+#
+# Returns: nothing on success
+#
+# Since: 1.1
+##
+{ 'command': 'dump', 'data': {'file': 'str'} }
diff --git a/qmp-commands.hx b/qmp-commands.hx
index 7e3f4b9..fefdae2 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -572,6 +572,32 @@ Example:
 EQMP
 
     {
+        .name       = "dump",
+        .args_type  = "file:s",
+        .params     = "file",
+        .help       = "dump to file",
+        .user_print = monitor_user_noop,
+        .mhandler.cmd_new = qmp_marshal_input_dump,
+    },
+
+SQMP
+dump
+
+
+Dump to file.
+
+Arguments:
+
+- "file": Destination file (json-string)
+
+Example:
+
+-> { "execute": "dump", "arguments": { "file": "fd:dump" } }
+<- { "return": {} }
+
+EQMP
+
+    {
         .name       = "netdev_add",
         .args_type  = "netdev:O",
         .params     = "[user|tap|socket],id=str[,prop=value][,...]",
-- 
1.7.1