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![David Hildenbrand](/assets/img/avatar_default.png)
For now, "share=off,readonly=on" would always result in us opening the file R/O and mmap'ing the opened file MAP_PRIVATE R/O -- effectively turning it into ROM. Especially for VM templating, "share=off" is a common use case. However, that use case is impossible with files that lack write permissions, because "share=off,readonly=on" will not give us writable RAM. The sole user of ROM via memory-backend-file are R/O NVDIMMs, but as we have users (Kata Containers) that rely on the existing behavior -- malicious VMs should not be able to consume COW memory for R/O NVDIMMs -- we cannot change the semantics of "share=off,readonly=on" So let's add a new "rom" property with on/off/auto values. "auto" is the default and what most people will use: for historical reasons, to not change the old semantics, it defaults to the value of the "readonly" property. For VM templating, one can now use: -object memory-backend-file,share=off,readonly=on,rom=off,... But we'll disallow: -object memory-backend-file,share=on,readonly=on,rom=off,... because we would otherwise get an error when trying to mmap the R/O file shared and writable. An explicit error message is cleaner. We will also disallow for now: -object memory-backend-file,share=off,readonly=off,rom=on,... -object memory-backend-file,share=on,readonly=off,rom=on,... It's not harmful, but also not really required for now. Alternatives that were abandoned: * Make "unarmed=on" for the NVDIMM set the memory region container readonly. We would still see a change of ROM->RAM and possibly run into memslot limits with vhost-user. Further, there might be use cases for "unarmed=on" that should still allow writing to that memory (temporary files, system RAM, ...). * Add a new "readonly=on/off/auto" parameter for NVDIMMs. Similar issues as with "unarmed=on". * Make "readonly" consume "on/off/file" instead of being a 'bool' type. This would slightly changes the behavior of the "readonly" parameter: values like true/false (as accepted by a 'bool'type) would no longer be accepted. Message-ID: <20230906120503.359863-4-david@redhat.com> Acked-by: Markus Armbruster <armbru@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com>
326 lines
9.6 KiB
C
326 lines
9.6 KiB
C
/*
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* QEMU Host Memory Backend for hugetlbfs
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*
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* Copyright (C) 2013-2014 Red Hat Inc
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*
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* Authors:
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* Paolo Bonzini <pbonzini@redhat.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or later.
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* See the COPYING file in the top-level directory.
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*/
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#include "qemu/osdep.h"
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#include "qapi/error.h"
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#include "qemu/error-report.h"
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#include "qemu/module.h"
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#include "qemu/madvise.h"
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#include "sysemu/hostmem.h"
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#include "qom/object_interfaces.h"
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#include "qom/object.h"
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#include "qapi/visitor.h"
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#include "qapi/qapi-visit-common.h"
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OBJECT_DECLARE_SIMPLE_TYPE(HostMemoryBackendFile, MEMORY_BACKEND_FILE)
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struct HostMemoryBackendFile {
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HostMemoryBackend parent_obj;
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char *mem_path;
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uint64_t align;
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uint64_t offset;
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bool discard_data;
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bool is_pmem;
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bool readonly;
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OnOffAuto rom;
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};
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static void
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file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
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{
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#ifndef CONFIG_POSIX
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error_setg(errp, "backend '%s' not supported on this host",
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object_get_typename(OBJECT(backend)));
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#else
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HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(backend);
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uint32_t ram_flags;
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gchar *name;
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if (!backend->size) {
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error_setg(errp, "can't create backend with size 0");
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return;
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}
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if (!fb->mem_path) {
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error_setg(errp, "mem-path property not set");
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return;
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}
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switch (fb->rom) {
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case ON_OFF_AUTO_AUTO:
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/* Traditionally, opening the file readonly always resulted in ROM. */
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fb->rom = fb->readonly ? ON_OFF_AUTO_ON : ON_OFF_AUTO_OFF;
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break;
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case ON_OFF_AUTO_ON:
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if (!fb->readonly) {
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error_setg(errp, "property 'rom' = 'on' is not supported with"
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" 'readonly' = 'off'");
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return;
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}
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break;
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case ON_OFF_AUTO_OFF:
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if (fb->readonly && backend->share) {
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error_setg(errp, "property 'rom' = 'off' is incompatible with"
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" 'readonly' = 'on' and 'share' = 'on'");
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return;
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}
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break;
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default:
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assert(false);
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}
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name = host_memory_backend_get_name(backend);
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ram_flags = backend->share ? RAM_SHARED : 0;
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ram_flags |= fb->readonly ? RAM_READONLY_FD : 0;
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ram_flags |= fb->rom == ON_OFF_AUTO_ON ? RAM_READONLY : 0;
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ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;
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ram_flags |= fb->is_pmem ? RAM_PMEM : 0;
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ram_flags |= RAM_NAMED_FILE;
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memory_region_init_ram_from_file(&backend->mr, OBJECT(backend), name,
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backend->size, fb->align, ram_flags,
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fb->mem_path, fb->offset, errp);
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g_free(name);
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#endif
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}
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static char *get_mem_path(Object *o, Error **errp)
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{
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HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
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return g_strdup(fb->mem_path);
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}
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static void set_mem_path(Object *o, const char *str, Error **errp)
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{
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HostMemoryBackend *backend = MEMORY_BACKEND(o);
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HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
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if (host_memory_backend_mr_inited(backend)) {
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error_setg(errp, "cannot change property 'mem-path' of %s",
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object_get_typename(o));
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return;
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}
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g_free(fb->mem_path);
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fb->mem_path = g_strdup(str);
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}
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static bool file_memory_backend_get_discard_data(Object *o, Error **errp)
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{
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return MEMORY_BACKEND_FILE(o)->discard_data;
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}
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static void file_memory_backend_set_discard_data(Object *o, bool value,
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Error **errp)
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{
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MEMORY_BACKEND_FILE(o)->discard_data = value;
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}
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static void file_memory_backend_get_align(Object *o, Visitor *v,
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const char *name, void *opaque,
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Error **errp)
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{
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HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
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uint64_t val = fb->align;
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visit_type_size(v, name, &val, errp);
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}
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static void file_memory_backend_set_align(Object *o, Visitor *v,
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const char *name, void *opaque,
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Error **errp)
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{
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HostMemoryBackend *backend = MEMORY_BACKEND(o);
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HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
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uint64_t val;
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if (host_memory_backend_mr_inited(backend)) {
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error_setg(errp, "cannot change property '%s' of %s", name,
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object_get_typename(o));
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return;
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}
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if (!visit_type_size(v, name, &val, errp)) {
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return;
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}
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fb->align = val;
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}
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static void file_memory_backend_get_offset(Object *o, Visitor *v,
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const char *name, void *opaque,
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Error **errp)
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{
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HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
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uint64_t val = fb->offset;
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visit_type_size(v, name, &val, errp);
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}
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static void file_memory_backend_set_offset(Object *o, Visitor *v,
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const char *name, void *opaque,
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Error **errp)
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{
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HostMemoryBackend *backend = MEMORY_BACKEND(o);
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HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
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uint64_t val;
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if (host_memory_backend_mr_inited(backend)) {
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error_setg(errp, "cannot change property '%s' of %s", name,
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object_get_typename(o));
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return;
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}
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if (!visit_type_size(v, name, &val, errp)) {
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return;
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}
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fb->offset = val;
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}
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#ifdef CONFIG_LIBPMEM
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static bool file_memory_backend_get_pmem(Object *o, Error **errp)
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{
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return MEMORY_BACKEND_FILE(o)->is_pmem;
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}
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static void file_memory_backend_set_pmem(Object *o, bool value, Error **errp)
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{
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HostMemoryBackend *backend = MEMORY_BACKEND(o);
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HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
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if (host_memory_backend_mr_inited(backend)) {
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error_setg(errp, "cannot change property 'pmem' of %s.",
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object_get_typename(o));
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return;
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}
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fb->is_pmem = value;
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}
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#endif /* CONFIG_LIBPMEM */
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static bool file_memory_backend_get_readonly(Object *obj, Error **errp)
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{
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HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(obj);
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return fb->readonly;
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}
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static void file_memory_backend_set_readonly(Object *obj, bool value,
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Error **errp)
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{
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HostMemoryBackend *backend = MEMORY_BACKEND(obj);
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HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(obj);
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if (host_memory_backend_mr_inited(backend)) {
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error_setg(errp, "cannot change property 'readonly' of %s.",
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object_get_typename(obj));
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return;
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}
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fb->readonly = value;
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}
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static void file_memory_backend_get_rom(Object *obj, Visitor *v,
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const char *name, void *opaque,
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Error **errp)
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{
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HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(obj);
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OnOffAuto rom = fb->rom;
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visit_type_OnOffAuto(v, name, &rom, errp);
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}
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static void file_memory_backend_set_rom(Object *obj, Visitor *v,
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const char *name, void *opaque,
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Error **errp)
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{
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HostMemoryBackend *backend = MEMORY_BACKEND(obj);
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HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(obj);
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if (host_memory_backend_mr_inited(backend)) {
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error_setg(errp, "cannot change property '%s' of %s.", name,
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object_get_typename(obj));
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return;
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}
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visit_type_OnOffAuto(v, name, &fb->rom, errp);
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}
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static void file_backend_unparent(Object *obj)
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{
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HostMemoryBackend *backend = MEMORY_BACKEND(obj);
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HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(obj);
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if (host_memory_backend_mr_inited(backend) && fb->discard_data) {
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void *ptr = memory_region_get_ram_ptr(&backend->mr);
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uint64_t sz = memory_region_size(&backend->mr);
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qemu_madvise(ptr, sz, QEMU_MADV_REMOVE);
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}
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}
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static void
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file_backend_class_init(ObjectClass *oc, void *data)
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{
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HostMemoryBackendClass *bc = MEMORY_BACKEND_CLASS(oc);
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bc->alloc = file_backend_memory_alloc;
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oc->unparent = file_backend_unparent;
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object_class_property_add_bool(oc, "discard-data",
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file_memory_backend_get_discard_data, file_memory_backend_set_discard_data);
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object_class_property_add_str(oc, "mem-path",
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get_mem_path, set_mem_path);
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object_class_property_add(oc, "align", "int",
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file_memory_backend_get_align,
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file_memory_backend_set_align,
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NULL, NULL);
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object_class_property_add(oc, "offset", "int",
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file_memory_backend_get_offset,
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file_memory_backend_set_offset,
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NULL, NULL);
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object_class_property_set_description(oc, "offset",
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"Offset into the target file (ex: 1G)");
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#ifdef CONFIG_LIBPMEM
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object_class_property_add_bool(oc, "pmem",
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file_memory_backend_get_pmem, file_memory_backend_set_pmem);
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#endif
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object_class_property_add_bool(oc, "readonly",
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file_memory_backend_get_readonly,
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file_memory_backend_set_readonly);
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object_class_property_add(oc, "rom", "OnOffAuto",
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file_memory_backend_get_rom, file_memory_backend_set_rom, NULL, NULL);
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object_class_property_set_description(oc, "rom",
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"Whether to create Read Only Memory (ROM)");
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}
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static void file_backend_instance_finalize(Object *o)
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{
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HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
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g_free(fb->mem_path);
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}
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static const TypeInfo file_backend_info = {
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.name = TYPE_MEMORY_BACKEND_FILE,
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.parent = TYPE_MEMORY_BACKEND,
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.class_init = file_backend_class_init,
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.instance_finalize = file_backend_instance_finalize,
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.instance_size = sizeof(HostMemoryBackendFile),
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};
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static void register_types(void)
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{
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type_register_static(&file_backend_info);
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}
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type_init(register_types);
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