qemu/backends/hostmem-file.c
Alexander Graf 4b870dc4d0 hostmem-file: add offset option
Add an option for hostmem-file to start the memory object at an offset
into the target file. This is useful if multiple memory objects reside
inside the same target file, such as a device node.

In particular, it's useful to map guest memory directly into /dev/mem
for experimentation.

To make this work consistently, also fix up all places in QEMU that
expect fd offsets to be 0.

Signed-off-by: Alexander Graf <graf@amazon.com>
Message-Id: <20230403221421.60877-1-graf@amazon.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Acked-by: Peter Xu <peterx@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
2023-05-23 16:47:03 +02:00

268 lines
7.6 KiB
C

/*
* QEMU Host Memory Backend for hugetlbfs
*
* Copyright (C) 2013-2014 Red Hat Inc
*
* Authors:
* Paolo Bonzini <pbonzini@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 "qapi/error.h"
#include "qemu/error-report.h"
#include "qemu/module.h"
#include "qemu/madvise.h"
#include "sysemu/hostmem.h"
#include "qom/object_interfaces.h"
#include "qom/object.h"
OBJECT_DECLARE_SIMPLE_TYPE(HostMemoryBackendFile, MEMORY_BACKEND_FILE)
struct HostMemoryBackendFile {
HostMemoryBackend parent_obj;
char *mem_path;
uint64_t align;
uint64_t offset;
bool discard_data;
bool is_pmem;
bool readonly;
};
static void
file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
{
#ifndef CONFIG_POSIX
error_setg(errp, "backend '%s' not supported on this host",
object_get_typename(OBJECT(backend)));
#else
HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(backend);
uint32_t ram_flags;
gchar *name;
if (!backend->size) {
error_setg(errp, "can't create backend with size 0");
return;
}
if (!fb->mem_path) {
error_setg(errp, "mem-path property not set");
return;
}
name = host_memory_backend_get_name(backend);
ram_flags = backend->share ? RAM_SHARED : 0;
ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;
ram_flags |= fb->is_pmem ? RAM_PMEM : 0;
memory_region_init_ram_from_file(&backend->mr, OBJECT(backend), name,
backend->size, fb->align, ram_flags,
fb->mem_path, fb->offset, fb->readonly,
errp);
g_free(name);
#endif
}
static char *get_mem_path(Object *o, Error **errp)
{
HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
return g_strdup(fb->mem_path);
}
static void set_mem_path(Object *o, const char *str, Error **errp)
{
HostMemoryBackend *backend = MEMORY_BACKEND(o);
HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
if (host_memory_backend_mr_inited(backend)) {
error_setg(errp, "cannot change property 'mem-path' of %s",
object_get_typename(o));
return;
}
g_free(fb->mem_path);
fb->mem_path = g_strdup(str);
}
static bool file_memory_backend_get_discard_data(Object *o, Error **errp)
{
return MEMORY_BACKEND_FILE(o)->discard_data;
}
static void file_memory_backend_set_discard_data(Object *o, bool value,
Error **errp)
{
MEMORY_BACKEND_FILE(o)->discard_data = value;
}
static void file_memory_backend_get_align(Object *o, Visitor *v,
const char *name, void *opaque,
Error **errp)
{
HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
uint64_t val = fb->align;
visit_type_size(v, name, &val, errp);
}
static void file_memory_backend_set_align(Object *o, Visitor *v,
const char *name, void *opaque,
Error **errp)
{
HostMemoryBackend *backend = MEMORY_BACKEND(o);
HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
uint64_t val;
if (host_memory_backend_mr_inited(backend)) {
error_setg(errp, "cannot change property '%s' of %s", name,
object_get_typename(o));
return;
}
if (!visit_type_size(v, name, &val, errp)) {
return;
}
fb->align = val;
}
static void file_memory_backend_get_offset(Object *o, Visitor *v,
const char *name, void *opaque,
Error **errp)
{
HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
uint64_t val = fb->offset;
visit_type_size(v, name, &val, errp);
}
static void file_memory_backend_set_offset(Object *o, Visitor *v,
const char *name, void *opaque,
Error **errp)
{
HostMemoryBackend *backend = MEMORY_BACKEND(o);
HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
uint64_t val;
if (host_memory_backend_mr_inited(backend)) {
error_setg(errp, "cannot change property '%s' of %s", name,
object_get_typename(o));
return;
}
if (!visit_type_size(v, name, &val, errp)) {
return;
}
fb->offset = val;
}
#ifdef CONFIG_LIBPMEM
static bool file_memory_backend_get_pmem(Object *o, Error **errp)
{
return MEMORY_BACKEND_FILE(o)->is_pmem;
}
static void file_memory_backend_set_pmem(Object *o, bool value, Error **errp)
{
HostMemoryBackend *backend = MEMORY_BACKEND(o);
HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
if (host_memory_backend_mr_inited(backend)) {
error_setg(errp, "cannot change property 'pmem' of %s.",
object_get_typename(o));
return;
}
fb->is_pmem = value;
}
#endif /* CONFIG_LIBPMEM */
static bool file_memory_backend_get_readonly(Object *obj, Error **errp)
{
HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(obj);
return fb->readonly;
}
static void file_memory_backend_set_readonly(Object *obj, bool value,
Error **errp)
{
HostMemoryBackend *backend = MEMORY_BACKEND(obj);
HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(obj);
if (host_memory_backend_mr_inited(backend)) {
error_setg(errp, "cannot change property 'readonly' of %s.",
object_get_typename(obj));
return;
}
fb->readonly = value;
}
static void file_backend_unparent(Object *obj)
{
HostMemoryBackend *backend = MEMORY_BACKEND(obj);
HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(obj);
if (host_memory_backend_mr_inited(backend) && fb->discard_data) {
void *ptr = memory_region_get_ram_ptr(&backend->mr);
uint64_t sz = memory_region_size(&backend->mr);
qemu_madvise(ptr, sz, QEMU_MADV_REMOVE);
}
}
static void
file_backend_class_init(ObjectClass *oc, void *data)
{
HostMemoryBackendClass *bc = MEMORY_BACKEND_CLASS(oc);
bc->alloc = file_backend_memory_alloc;
oc->unparent = file_backend_unparent;
object_class_property_add_bool(oc, "discard-data",
file_memory_backend_get_discard_data, file_memory_backend_set_discard_data);
object_class_property_add_str(oc, "mem-path",
get_mem_path, set_mem_path);
object_class_property_add(oc, "align", "int",
file_memory_backend_get_align,
file_memory_backend_set_align,
NULL, NULL);
object_class_property_add(oc, "offset", "int",
file_memory_backend_get_offset,
file_memory_backend_set_offset,
NULL, NULL);
object_class_property_set_description(oc, "offset",
"Offset into the target file (ex: 1G)");
#ifdef CONFIG_LIBPMEM
object_class_property_add_bool(oc, "pmem",
file_memory_backend_get_pmem, file_memory_backend_set_pmem);
#endif
object_class_property_add_bool(oc, "readonly",
file_memory_backend_get_readonly,
file_memory_backend_set_readonly);
}
static void file_backend_instance_finalize(Object *o)
{
HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
g_free(fb->mem_path);
}
static const TypeInfo file_backend_info = {
.name = TYPE_MEMORY_BACKEND_FILE,
.parent = TYPE_MEMORY_BACKEND,
.class_init = file_backend_class_init,
.instance_finalize = file_backend_instance_finalize,
.instance_size = sizeof(HostMemoryBackendFile),
};
static void register_types(void)
{
type_register_static(&file_backend_info);
}
type_init(register_types);