[Qemu-devel] [RFC][PATCH 09/14 v7] introduce a new monitor command 'dump' to dump guest's memory

[Wen Congyang]

Signed-off-by: Wen Congyang <address@hidden>
---
 Makefile.target  |    2 +-
 dump.c           |  637 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 hmp-commands.hx  |   20 ++
 hmp.c            |    9 +
 hmp.h            |    1 +
 qapi-schema.json |   13 ++
 qmp-commands.hx  |   29 +++
 7 files changed, 710 insertions(+), 1 deletions(-)
 create mode 100644 dump.c

diff --git a/Makefile.target b/Makefile.target
index cfd3113..4ae59f5 100644
--- a/Makefile.target
+++ b/Makefile.target
@@ -210,7 +210,7 @@ obj-$(CONFIG_NO_KVM) += kvm-stub.o
 obj-$(CONFIG_VGA) += vga.o
 obj-y += memory.o savevm.o
 obj-y += memory_mapping.o
-obj-$(CONFIG_HAVE_CORE_DUMP) += arch_dump.o
+obj-$(CONFIG_HAVE_CORE_DUMP) += arch_dump.o dump.o
 LIBS+=-lz
 
 obj-i386-$(CONFIG_KVM) += hyperv.o
diff --git a/dump.c b/dump.c
new file mode 100644
index 0000000..c9baedb
--- /dev/null
+++ b/dump.c
@@ -0,0 +1,637 @@
+/*
+ * QEMU dump
+ *
+ * Copyright Fujitsu, Corp. 2011
+ *
+ * Authors:
+ *     Wen Congyang <address@hidden>
+ *
+ * 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"
+#include "gdbstub.h"
+
+static inline uint16_t cpu_contert_to_target16(uint16_t val, int endian)
+{
+    if (endian == ELFDATA2LSB) {
+        val = cpu_to_le16(val);
+    } else {
+        val = cpu_to_be16(val);
+    }
+
+    return val;
+}
+
+static inline uint32_t cpu_contert_to_target32(uint32_t val, int endian)
+{
+    if (endian == ELFDATA2LSB) {
+        val = cpu_to_le32(val);
+    } else {
+        val = cpu_to_be32(val);
+    }
+
+    return val;
+}
+
+static inline uint64_t cpu_contert_to_target64(uint64_t val, int endian)
+{
+    if (endian == ELFDATA2LSB) {
+        val = cpu_to_le64(val);
+    } else {
+        val = cpu_to_be64(val);
+    }
+
+    return 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;
+    bool resume;
+    char *error;
+    target_phys_addr_t memory_offset;
+    write_core_dump_function f;
+    void (*cleanup)(void *opaque);
+    void *opaque;
+} 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;
+
+    memory_mapping_list_free(&s->list);
+    s->cleanup(s->opaque);
+    if (s->resume) {
+        vm_start();
+    }
+
+    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 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_contert_to_target16(ET_CORE, endian);
+    elf_header.e_machine = cpu_contert_to_target16(s->dump_info.d_machine,
+                                                   endian);
+    elf_header.e_version = cpu_contert_to_target32(EV_CURRENT, endian);
+    elf_header.e_ehsize = cpu_contert_to_target16(sizeof(elf_header), endian);
+    elf_header.e_phoff = cpu_contert_to_target64(sizeof(Elf64_Ehdr), endian);
+    elf_header.e_phentsize = cpu_contert_to_target16(sizeof(Elf64_Phdr), 
endian);
+    elf_header.e_phnum = cpu_contert_to_target16(s->phdr_num, endian);
+
+    ret = s->f(0, &elf_header, sizeof(elf_header), s->opaque);
+    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_contert_to_target16(ET_CORE, endian);
+    elf_header.e_machine = cpu_contert_to_target16(s->dump_info.d_machine,
+                                                   endian);
+    elf_header.e_version = cpu_contert_to_target32(EV_CURRENT, endian);
+    elf_header.e_ehsize = cpu_contert_to_target16(sizeof(elf_header), endian);
+    elf_header.e_phoff = cpu_contert_to_target32(sizeof(Elf32_Ehdr), endian);
+    elf_header.e_phentsize = cpu_contert_to_target16(sizeof(Elf32_Phdr),
+                                                     endian);
+    elf_header.e_phnum = cpu_contert_to_target16(s->phdr_num, endian);
+
+    ret = s->f(0, &elf_header, sizeof(elf_header), s->opaque);
+    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_contert_to_target32(PT_LOAD, endian);
+    phdr.p_offset = cpu_contert_to_target64(offset, endian);
+    phdr.p_paddr = cpu_contert_to_target64(memory_mapping->phys_addr, endian);
+    if (offset == -1) {
+        phdr.p_filesz = 0;
+    } else {
+        phdr.p_filesz = cpu_contert_to_target64(memory_mapping->length, 
endian);
+    }
+    phdr.p_memsz = cpu_contert_to_target64(memory_mapping->length, endian);
+    phdr.p_vaddr = cpu_contert_to_target64(memory_mapping->virt_addr, endian);
+
+    phdr_offset = sizeof(Elf64_Ehdr) + sizeof(Elf64_Phdr)*phdr_index;
+    ret = s->f(phdr_offset, &phdr, sizeof(Elf64_Phdr), s->opaque);
+    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_contert_to_target32(PT_LOAD, endian);
+    phdr.p_offset = cpu_contert_to_target32(offset, endian);
+    phdr.p_paddr = cpu_contert_to_target32(memory_mapping->phys_addr, endian);
+    if (offset == -1) {
+        phdr.p_filesz = 0;
+    } else {
+        phdr.p_filesz = cpu_contert_to_target32(memory_mapping->length, 
endian);
+    }
+    phdr.p_memsz = cpu_contert_to_target32(memory_mapping->length, endian);
+    phdr.p_vaddr = cpu_contert_to_target32(memory_mapping->virt_addr, endian);
+
+    phdr_offset = sizeof(Elf32_Ehdr) + sizeof(Elf32_Phdr)*phdr_index;
+    ret = s->f(phdr_offset, &phdr, sizeof(Elf32_Phdr), s->opaque);
+    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 = gdb_id(env);
+        ret = cpu_write_elf64_note(s->f, env, id, offset, s->opaque);
+        if (ret < 0) {
+            dump_error(s, "dump: failed to write elf notes.\n");
+            return -1;
+        }
+    }
+
+    for (env = first_cpu; env != NULL; env = env->next_cpu) {
+        ret = cpu_write_elf64_qemunote(s->f, env, offset, s->opaque);
+        if (ret < 0) {
+            dump_error(s, "dump: failed to write CPU status.\n");
+            return -1;
+        }
+    }
+
+    memset(&phdr, 0, sizeof(Elf64_Phdr));
+    phdr.p_type = cpu_contert_to_target32(PT_NOTE, endian);
+    phdr.p_offset = cpu_contert_to_target64(begin, endian);
+    phdr.p_paddr = 0;
+    phdr.p_filesz = cpu_contert_to_target64(*offset - begin, endian);
+    phdr.p_memsz = cpu_contert_to_target64(*offset - begin, endian);
+    phdr.p_vaddr = 0;
+
+    phdr_offset = sizeof(Elf64_Ehdr);
+    ret = s->f(phdr_offset, &phdr, sizeof(Elf64_Phdr), s->opaque);
+    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 = gdb_id(env);
+        ret = cpu_write_elf32_note(s->f, env, id, offset, s->opaque);
+        if (ret < 0) {
+            dump_error(s, "dump: failed to write elf notes.\n");
+            return -1;
+        }
+    }
+
+    for (env = first_cpu; env != NULL; env = env->next_cpu) {
+        ret = cpu_write_elf32_qemunote(s->f, env, offset, s->opaque);
+        if (ret < 0) {
+            dump_error(s, "dump: failed to write CPU status.\n");
+            return -1;
+        }
+    }
+
+    memset(&phdr, 0, sizeof(Elf32_Phdr));
+    phdr.p_type = cpu_contert_to_target32(PT_NOTE, endian);
+    phdr.p_offset = cpu_contert_to_target32(begin, endian);
+    phdr.p_paddr = 0;
+    phdr.p_filesz = cpu_contert_to_target32(*offset - begin, endian);
+    phdr.p_memsz = cpu_contert_to_target32(*offset - begin, endian);
+    phdr.p_vaddr = 0;
+
+    phdr_offset = sizeof(Elf32_Ehdr);
+    ret = s->f(phdr_offset, &phdr, sizeof(Elf32_Phdr), s->opaque);
+    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;
+
+    ret = s->f(*offset, buf, length, s->opaque);
+    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;
+}
+
+/* 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;
+}
+
+static DumpState *dump_init(Error **errp)
+{
+    CPUState *env;
+    DumpState *s = dump_get_current();
+    int ret;
+
+    if (runstate_is_running()) {
+        vm_stop(RUN_STATE_PAUSED);
+        s->resume = true;
+    } else {
+        s->resume = false;
+    }
+    s->state = DUMP_STATE_SETUP;
+    if (s->error) {
+        g_free(s->error);
+        s->error = NULL;
+    }
+
+    /*
+     * 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 */
+    memory_mapping_list_init(&s->list);
+    qemu_get_guest_memory_mapping(&s->list);
+
+    /*
+     * 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;
+}
+
+static int fd_write_vmcore(target_phys_addr_t offset, void *buf, size_t size,
+                           void *opaque)
+{
+    int fd = (int)(intptr_t)opaque;
+    int ret;
+
+    ret = lseek(fd, offset, SEEK_SET);
+    if (ret < 0) {
+        return -1;
+    }
+
+    ret = write(fd, buf, size);
+    if (ret != size) {
+        return -1;
+    }
+
+    return 0;
+}
+
+static void fd_cleanup(void *opaque)
+{
+    int fd = (int)(intptr_t)opaque;
+
+    if (fd != -1) {
+        close(fd);
+    }
+}
+
+static DumpState *dump_init_fd(int fd, Error **errp)
+{
+    DumpState *s = dump_init(errp);
+
+    if (s == NULL) {
+        return NULL;
+    }
+
+    s->f = fd_write_vmcore;
+    s->cleanup = fd_cleanup;
+    s->opaque = (void *)(intptr_t)fd;
+
+    return s;
+}
+
+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, S_IRUSR);
+        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(fd, errp);
+    if (!s) {
+        return;
+    }
+
+    if (create_vmcore(s) < 0) {
+        error_set(errp, QERR_IO_ERROR);
+    }
+
+    return;
+}
diff --git a/hmp-commands.hx b/hmp-commands.hx
index 64b3656..19200ad 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -880,6 +880,26 @@ server will ask the spice/vnc client to automatically 
reconnect using the
 new parameters (if specified) once the vm migration finished successfully.
 ETEXI
 
+#if defined(CONFIG_HAVE_CORE_DUMP)
+    {
+        .name       = "dump",
+        .args_type  = "file:s",
+        .params     = "file",
+        .help       = "dump to file",
+        .user_print = monitor_user_noop,
+        .mhandler.cmd = hmp_dump,
+    },
+
+
+STEXI
address@hidden dump @var{file}
address@hidden dump
+Dump to @var{file}. The file can be processed with crash or gdb.
+    file: destination file(started with "file:") or destination file descriptor
+          (started with "fd:")
+ETEXI
+#endif
+
     {
         .name       = "snapshot_blkdev",
         .args_type  = "device:B,snapshot-file:s?,format:s?",
diff --git a/hmp.c b/hmp.c
index 3a54455..309ccec 100644
--- a/hmp.c
+++ b/hmp.c
@@ -856,3 +856,12 @@ void hmp_block_job_cancel(Monitor *mon, const QDict *qdict)
 
     hmp_handle_error(mon, &error);
 }
+
+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 5409464..b055e50 100644
--- a/hmp.h
+++ b/hmp.h
@@ -59,5 +59,6 @@ void hmp_block_set_io_throttle(Monitor *mon, const QDict 
*qdict);
 void hmp_block_stream(Monitor *mon, const QDict *qdict);
 void hmp_block_job_set_speed(Monitor *mon, const QDict *qdict);
 void hmp_block_job_cancel(Monitor *mon, const QDict *qdict);
+void hmp_dump(Monitor *mon, const QDict *qdict);
 
 #endif
diff --git a/qapi-schema.json b/qapi-schema.json
index d0b6792..3c4aa70 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -1593,3 +1593,16 @@
 { 'command': 'qom-list-types',
   'data': { '*implements': 'str', '*abstract': 'bool' },
   'returns': [ 'ObjectTypeInfo' ] }
+
+##
+# @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 705f704..1199316 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -586,6 +586,35 @@ Example:
 
 EQMP
 
+#if defined(CONFIG_HAVE_CORE_DUMP)
+    {
+        .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. The file can be processed with crash or gdb.
+
+Arguments:
+
+- "file": destination file(started with "file:") or destination file descriptor
+          (started with "fd:") (json-string)
+
+Example:
+
+-> { "execute": "dump", "arguments": { "file": "fd:dump" } }
+<- { "return": {} }
+
+EQMP
+#endif
+
     {
         .name       = "netdev_add",
         .args_type  = "netdev:O",
-- 
1.7.1