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qemu/migration/vmstate.c
Peter Xu 579cedf430 migration: Unify and trace vmstate field_exists() checks 
For both save/load we actually share the logic on deciding whether a field
should exist.  Merge the checks into a helper and use it for both save and
load.  When doing so, add documentations and reformat the code to make it
much easier to read.

The real benefit here (besides code cleanups) is we add a trace-point for
this; this is a known spot where we can easily break migration
compatibilities between binaries, and this trace point will be critical for
us to identify such issues.

For example, this will be handy when debugging things like:

https://gitlab.com/qemu-project/qemu/-/issues/932

Reviewed-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Message-ID: <20230906204722.514474-1-peterx@redhat.com>
2023-10-04 13:19:47 +02:00

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/*
* VMState interpreter
*
* Copyright (c) 2009-2017 Red Hat Inc
*
* Authors:
* Juan Quintela <quintela@redhat.com>
*
* This work is licensed under the terms of the GNU GPL, version 2 or later.
* See the COPYING file in the top-level directory.
*/
#include "qemu/osdep.h"
#include "migration.h"
#include "migration/vmstate.h"
#include "savevm.h"
#include "qapi/error.h"
#include "qapi/qmp/json-writer.h"
#include "qemu-file.h"
#include "qemu/bitops.h"
#include "qemu/error-report.h"
#include "trace.h"
static int vmstate_subsection_save(QEMUFile *f, const VMStateDescription *vmsd,
void *opaque, JSONWriter *vmdesc);
static int vmstate_subsection_load(QEMUFile *f, const VMStateDescription *vmsd,
void *opaque);
/* Whether this field should exist for either save or load the VM? */
static bool
vmstate_field_exists(const VMStateDescription *vmsd, const VMStateField *field,
void *opaque, int version_id)
{
bool result;
if (field->field_exists) {
/* If there's the function checker, that's the solo truth */
result = field->field_exists(opaque, version_id);
trace_vmstate_field_exists(vmsd->name, field->name, field->version_id,
version_id, result);
} else {
/*
* Otherwise, we only save/load if field version is same or older.
* For example, when loading from an old binary with old version,
* we ignore new fields with newer version_ids.
*/
result = field->version_id <= version_id;
}
return result;
}
static int vmstate_n_elems(void *opaque, const VMStateField *field)
{
int n_elems = 1;
if (field->flags & VMS_ARRAY) {
n_elems = field->num;
} else if (field->flags & VMS_VARRAY_INT32) {
n_elems = *(int32_t *)(opaque + field->num_offset);
} else if (field->flags & VMS_VARRAY_UINT32) {
n_elems = *(uint32_t *)(opaque + field->num_offset);
} else if (field->flags & VMS_VARRAY_UINT16) {
n_elems = *(uint16_t *)(opaque + field->num_offset);
} else if (field->flags & VMS_VARRAY_UINT8) {
n_elems = *(uint8_t *)(opaque + field->num_offset);
}
if (field->flags & VMS_MULTIPLY_ELEMENTS) {
n_elems *= field->num;
}
trace_vmstate_n_elems(field->name, n_elems);
return n_elems;
}
static int vmstate_size(void *opaque, const VMStateField *field)
{
int size = field->size;
if (field->flags & VMS_VBUFFER) {
size = *(int32_t *)(opaque + field->size_offset);
if (field->flags & VMS_MULTIPLY) {
size *= field->size;
}
}
return size;
}
static void vmstate_handle_alloc(void *ptr, const VMStateField *field,
void *opaque)
{
if (field->flags & VMS_POINTER && field->flags & VMS_ALLOC) {
gsize size = vmstate_size(opaque, field);
size *= vmstate_n_elems(opaque, field);
if (size) {
*(void **)ptr = g_malloc(size);
}
}
}
int vmstate_load_state(QEMUFile *f, const VMStateDescription *vmsd,
void *opaque, int version_id)
{
const VMStateField *field = vmsd->fields;
int ret = 0;
trace_vmstate_load_state(vmsd->name, version_id);
if (version_id > vmsd->version_id) {
error_report("%s: incoming version_id %d is too new "
"for local version_id %d",
vmsd->name, version_id, vmsd->version_id);
trace_vmstate_load_state_end(vmsd->name, "too new", -EINVAL);
return -EINVAL;
}
if (version_id < vmsd->minimum_version_id) {
error_report("%s: incoming version_id %d is too old "
"for local minimum version_id %d",
vmsd->name, version_id, vmsd->minimum_version_id);
trace_vmstate_load_state_end(vmsd->name, "too old", -EINVAL);
return -EINVAL;
}
if (vmsd->pre_load) {
ret = vmsd->pre_load(opaque);
if (ret) {
return ret;
}
}
while (field->name) {
trace_vmstate_load_state_field(vmsd->name, field->name);
if (vmstate_field_exists(vmsd, field, opaque, version_id)) {
void *first_elem = opaque + field->offset;
int i, n_elems = vmstate_n_elems(opaque, field);
int size = vmstate_size(opaque, field);
vmstate_handle_alloc(first_elem, field, opaque);
if (field->flags & VMS_POINTER) {
first_elem = *(void **)first_elem;
assert(first_elem || !n_elems || !size);
}
for (i = 0; i < n_elems; i++) {
void *curr_elem = first_elem + size * i;
if (field->flags & VMS_ARRAY_OF_POINTER) {
curr_elem = *(void **)curr_elem;
}
if (!curr_elem && size) {
/* if null pointer check placeholder and do not follow */
assert(field->flags & VMS_ARRAY_OF_POINTER);
ret = vmstate_info_nullptr.get(f, curr_elem, size, NULL);
} else if (field->flags & VMS_STRUCT) {
ret = vmstate_load_state(f, field->vmsd, curr_elem,
field->vmsd->version_id);
} else if (field->flags & VMS_VSTRUCT) {
ret = vmstate_load_state(f, field->vmsd, curr_elem,
field->struct_version_id);
} else {
ret = field->info->get(f, curr_elem, size, field);
}
if (ret >= 0) {
ret = qemu_file_get_error(f);
}
if (ret < 0) {
qemu_file_set_error(f, ret);
error_report("Failed to load %s:%s", vmsd->name,
field->name);
trace_vmstate_load_field_error(field->name, ret);
return ret;
}
}
} else if (field->flags & VMS_MUST_EXIST) {
error_report("Input validation failed: %s/%s",
vmsd->name, field->name);
return -1;
}
field++;
}
assert(field->flags == VMS_END);
ret = vmstate_subsection_load(f, vmsd, opaque);
if (ret != 0) {
return ret;
}
if (vmsd->post_load) {
ret = vmsd->post_load(opaque, version_id);
}
trace_vmstate_load_state_end(vmsd->name, "end", ret);
return ret;
}
static int vmfield_name_num(const VMStateField *start,
const VMStateField *search)
{
const VMStateField *field;
int found = 0;
for (field = start; field->name; field++) {
if (!strcmp(field->name, search->name)) {
if (field == search) {
return found;
}
found++;
}
}
return -1;
}
static bool vmfield_name_is_unique(const VMStateField *start,
const VMStateField *search)
{
const VMStateField *field;
int found = 0;
for (field = start; field->name; field++) {
if (!strcmp(field->name, search->name)) {
found++;
/* name found more than once, so it's not unique */
if (found > 1) {
return false;
}
}
}
return true;
}
static const char *vmfield_get_type_name(const VMStateField *field)
{
const char *type = "unknown";
if (field->flags & VMS_STRUCT) {
type = "struct";
} else if (field->flags & VMS_VSTRUCT) {
type = "vstruct";
} else if (field->info->name) {
type = field->info->name;
}
return type;
}
static bool vmsd_can_compress(const VMStateField *field)
{
if (field->field_exists) {
/* Dynamically existing fields mess up compression */
return false;
}
if (field->flags & VMS_STRUCT) {
const VMStateField *sfield = field->vmsd->fields;
while (sfield->name) {
if (!vmsd_can_compress(sfield)) {
/* Child elements can't compress, so can't we */
return false;
}
sfield++;
}
if (field->vmsd->subsections) {
/* Subsections may come and go, better don't compress */
return false;
}
}
return true;
}
static void vmsd_desc_field_start(const VMStateDescription *vmsd,
JSONWriter *vmdesc,
const VMStateField *field, int i, int max)
{
char *name, *old_name;
bool is_array = max > 1;
bool can_compress = vmsd_can_compress(field);
if (!vmdesc) {
return;
}
name = g_strdup(field->name);
/* Field name is not unique, need to make it unique */
if (!vmfield_name_is_unique(vmsd->fields, field)) {
int num = vmfield_name_num(vmsd->fields, field);
old_name = name;
name = g_strdup_printf("%s[%d]", name, num);
g_free(old_name);
}
json_writer_start_object(vmdesc, NULL);
json_writer_str(vmdesc, "name", name);
if (is_array) {
if (can_compress) {
json_writer_int64(vmdesc, "array_len", max);
} else {
json_writer_int64(vmdesc, "index", i);
}
}
json_writer_str(vmdesc, "type", vmfield_get_type_name(field));
if (field->flags & VMS_STRUCT) {
json_writer_start_object(vmdesc, "struct");
}
g_free(name);
}
static void vmsd_desc_field_end(const VMStateDescription *vmsd,
JSONWriter *vmdesc,
const VMStateField *field, size_t size, int i)
{
if (!vmdesc) {
return;
}
if (field->flags & VMS_STRUCT) {
/* We printed a struct in between, close its child object */
json_writer_end_object(vmdesc);
}
json_writer_int64(vmdesc, "size", size);
json_writer_end_object(vmdesc);
}
bool vmstate_save_needed(const VMStateDescription *vmsd, void *opaque)
{
if (vmsd->needed && !vmsd->needed(opaque)) {
/* optional section not needed */
return false;
}
return true;
}
int vmstate_save_state(QEMUFile *f, const VMStateDescription *vmsd,
void *opaque, JSONWriter *vmdesc_id)
{
return vmstate_save_state_v(f, vmsd, opaque, vmdesc_id, vmsd->version_id, NULL);
}
int vmstate_save_state_with_err(QEMUFile *f, const VMStateDescription *vmsd,
void *opaque, JSONWriter *vmdesc_id, Error **errp)
{
return vmstate_save_state_v(f, vmsd, opaque, vmdesc_id, vmsd->version_id, errp);
}
int vmstate_save_state_v(QEMUFile *f, const VMStateDescription *vmsd,
void *opaque, JSONWriter *vmdesc, int version_id, Error **errp)
{
int ret = 0;
const VMStateField *field = vmsd->fields;
trace_vmstate_save_state_top(vmsd->name);
if (vmsd->pre_save) {
ret = vmsd->pre_save(opaque);
trace_vmstate_save_state_pre_save_res(vmsd->name, ret);
if (ret) {
error_setg(errp, "pre-save failed: %s", vmsd->name);
return ret;
}
}
if (vmdesc) {
json_writer_str(vmdesc, "vmsd_name", vmsd->name);
json_writer_int64(vmdesc, "version", version_id);
json_writer_start_array(vmdesc, "fields");
}
while (field->name) {
if (vmstate_field_exists(vmsd, field, opaque, version_id)) {
void *first_elem = opaque + field->offset;
int i, n_elems = vmstate_n_elems(opaque, field);
int size = vmstate_size(opaque, field);
uint64_t old_offset, written_bytes;
JSONWriter *vmdesc_loop = vmdesc;
trace_vmstate_save_state_loop(vmsd->name, field->name, n_elems);
if (field->flags & VMS_POINTER) {
first_elem = *(void **)first_elem;
assert(first_elem || !n_elems || !size);
}
for (i = 0; i < n_elems; i++) {
void *curr_elem = first_elem + size * i;
vmsd_desc_field_start(vmsd, vmdesc_loop, field, i, n_elems);
old_offset = qemu_file_transferred_noflush(f);
if (field->flags & VMS_ARRAY_OF_POINTER) {
assert(curr_elem);
curr_elem = *(void **)curr_elem;
}
if (!curr_elem && size) {
/* if null pointer write placeholder and do not follow */
assert(field->flags & VMS_ARRAY_OF_POINTER);
ret = vmstate_info_nullptr.put(f, curr_elem, size, NULL,
NULL);
} else if (field->flags & VMS_STRUCT) {
ret = vmstate_save_state(f, field->vmsd, curr_elem,
vmdesc_loop);
} else if (field->flags & VMS_VSTRUCT) {
ret = vmstate_save_state_v(f, field->vmsd, curr_elem,
vmdesc_loop,
field->struct_version_id, errp);
} else {
ret = field->info->put(f, curr_elem, size, field,
vmdesc_loop);
}
if (ret) {
error_setg(errp, "Save of field %s/%s failed",
vmsd->name, field->name);
if (vmsd->post_save) {
vmsd->post_save(opaque);
}
return ret;
}
written_bytes = qemu_file_transferred_noflush(f) - old_offset;
vmsd_desc_field_end(vmsd, vmdesc_loop, field, written_bytes, i);
/* Compressed arrays only care about the first element */
if (vmdesc_loop && vmsd_can_compress(field)) {
vmdesc_loop = NULL;
}
}
} else {
if (field->flags & VMS_MUST_EXIST) {
error_report("Output state validation failed: %s/%s",
vmsd->name, field->name);
assert(!(field->flags & VMS_MUST_EXIST));
}
}
field++;
}
assert(field->flags == VMS_END);
if (vmdesc) {
json_writer_end_array(vmdesc);
}
ret = vmstate_subsection_save(f, vmsd, opaque, vmdesc);
if (vmsd->post_save) {
int ps_ret = vmsd->post_save(opaque);
if (!ret) {
ret = ps_ret;
}
}
return ret;
}
static const VMStateDescription *
vmstate_get_subsection(const VMStateDescription **sub, char *idstr)
{
while (sub && *sub) {
if (strcmp(idstr, (*sub)->name) == 0) {
return *sub;
}
sub++;
}
return NULL;
}
static int vmstate_subsection_load(QEMUFile *f, const VMStateDescription *vmsd,
void *opaque)
{
trace_vmstate_subsection_load(vmsd->name);
while (qemu_peek_byte(f, 0) == QEMU_VM_SUBSECTION) {
char idstr[256], *idstr_ret;
int ret;
uint8_t version_id, len, size;
const VMStateDescription *sub_vmsd;
len = qemu_peek_byte(f, 1);
if (len < strlen(vmsd->name) + 1) {
/* subsection name has be be "section_name/a" */
trace_vmstate_subsection_load_bad(vmsd->name, "(short)", "");
return 0;
}
size = qemu_peek_buffer(f, (uint8_t **)&idstr_ret, len, 2);
if (size != len) {
trace_vmstate_subsection_load_bad(vmsd->name, "(peek fail)", "");
return 0;
}
memcpy(idstr, idstr_ret, size);
idstr[size] = 0;
if (strncmp(vmsd->name, idstr, strlen(vmsd->name)) != 0) {
trace_vmstate_subsection_load_bad(vmsd->name, idstr, "(prefix)");
/* it doesn't have a valid subsection name */
return 0;
}
sub_vmsd = vmstate_get_subsection(vmsd->subsections, idstr);
if (sub_vmsd == NULL) {
trace_vmstate_subsection_load_bad(vmsd->name, idstr, "(lookup)");
return -ENOENT;
}
qemu_file_skip(f, 1); /* subsection */
qemu_file_skip(f, 1); /* len */
qemu_file_skip(f, len); /* idstr */
version_id = qemu_get_be32(f);
ret = vmstate_load_state(f, sub_vmsd, opaque, version_id);
if (ret) {
trace_vmstate_subsection_load_bad(vmsd->name, idstr, "(child)");
return ret;
}
}
trace_vmstate_subsection_load_good(vmsd->name);
return 0;
}
static int vmstate_subsection_save(QEMUFile *f, const VMStateDescription *vmsd,
void *opaque, JSONWriter *vmdesc)
{
const VMStateDescription **sub = vmsd->subsections;
bool vmdesc_has_subsections = false;
int ret = 0;
trace_vmstate_subsection_save_top(vmsd->name);
while (sub && *sub) {
if (vmstate_save_needed(*sub, opaque)) {
const VMStateDescription *vmsdsub = *sub;
uint8_t len;
trace_vmstate_subsection_save_loop(vmsd->name, vmsdsub->name);
if (vmdesc) {
/* Only create subsection array when we have any */
if (!vmdesc_has_subsections) {
json_writer_start_array(vmdesc, "subsections");
vmdesc_has_subsections = true;
}
json_writer_start_object(vmdesc, NULL);
}
qemu_put_byte(f, QEMU_VM_SUBSECTION);
len = strlen(vmsdsub->name);
qemu_put_byte(f, len);
qemu_put_buffer(f, (uint8_t *)vmsdsub->name, len);
qemu_put_be32(f, vmsdsub->version_id);
ret = vmstate_save_state(f, vmsdsub, opaque, vmdesc);
if (ret) {
return ret;
}
if (vmdesc) {
json_writer_end_object(vmdesc);
}
}
sub++;
}
if (vmdesc_has_subsections) {
json_writer_end_array(vmdesc);
}
return ret;
}
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