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hostmem-file: add offset option

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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>
This commit is contained in:
Alexander Graf 2023-04-03 22:14:21 +00:00 • committed by David Hildenbrand
parent 886c0453cb
commit 4b870dc4d0
9 changed files with 69 additions and 9 deletions
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40
backends/hostmem-file.c
View file

@ -27,6 +27,7 @@ struct HostMemoryBackendFile {
char *mem_path;
uint64_t align;
uint64_t offset;
bool discard_data;
bool is_pmem;
bool readonly;
@ -58,7 +59,8 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
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->readonly, errp);
fb->mem_path, fb->offset, fb->readonly,
errp);
g_free(name);
#endif
}
@ -125,6 +127,36 @@ static void file_memory_backend_set_align(Object *o, Visitor *v,
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)
{
@ -197,6 +229,12 @@ file_backend_class_init(ObjectClass *oc, void *data)
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);