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.
Signed-off-by: Alexander Graf <g...@amazon.com>
Reviewed-by: Stefan Hajnoczi <stefa...@gmail.com>
---
v1 -> v2:
- add qom documentation
- propagate offset into truncate, size and alignment checks
v2 -> v3:
- fix typo
---
backends/hostmem-file.c | 40 +++++++++++++++++++++++++++++++++++++++-
include/exec/memory.h | 2 ++
include/exec/ram_addr.h | 3 ++-
qapi/qom.json | 5 +++++
qemu-options.hx | 6 +++++-
softmmu/memory.c | 3 ++-
softmmu/physmem.c | 14 ++++++++++----
7 files changed, 65 insertions(+), 8 deletions(-)
diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
index 25141283c4..38ea65bec5 100644
--- a/backends/hostmem-file.c
+++ b/backends/hostmem-file.c
@@ -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);
diff --git a/include/exec/memory.h b/include/exec/memory.h
index 15ade918ba..3b7295fbe2 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -1318,6 +1318,7 @@ void memory_region_init_resizeable_ram(MemoryRegion *mr,
* @ram_flags: RamBlock flags. Supported flags: RAM_SHARED, RAM_PMEM,
* RAM_NORESERVE,
* @path: the path in which to allocate the RAM.
+ * @offset: offset within the file referenced by path
* @readonly: true to open @path for reading, false for read/write.
* @errp: pointer to Error*, to store an error if it happens.
*
@@ -1331,6 +1332,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
uint64_t align,
uint32_t ram_flags,
const char *path,
+ ram_addr_t offset,
bool readonly,
Error **errp);
diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
index f4fb6a2111..90a8269290 100644
--- a/include/exec/ram_addr.h
+++ b/include/exec/ram_addr.h
@@ -110,6 +110,7 @@ long qemu_maxrampagesize(void);
* @ram_flags: RamBlock flags. Supported flags: RAM_SHARED, RAM_PMEM,
* RAM_NORESERVE.
* @mem_path or @fd: specify the backing file or device
+ * @offset: Offset into target file
* @readonly: true to open @path for reading, false for read/write.
* @errp: pointer to Error*, to store an error if it happens
*
@@ -119,7 +120,7 @@ long qemu_maxrampagesize(void);
*/
RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
uint32_t ram_flags, const char *mem_path,
- bool readonly, Error **errp);
+ off_t offset, bool readonly, Error **errp);
RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
uint32_t ram_flags, int fd, off_t offset,
bool readonly, Error **errp);
diff --git a/qapi/qom.json b/qapi/qom.json
index a877b879b9..8f5eaa8415 100644
--- a/qapi/qom.json
+++ b/qapi/qom.json
@@ -635,6 +635,10 @@
# specify the required alignment via this option.
# 0 selects a default alignment (currently the page size). (default: 0)
#
+# @offset: the offset into the target file that the region starts at. You can
+# use this option to overload multiple regions into a single fils.
+# (default: 0)
+#
# @discard-data: if true, the file contents can be destroyed when QEMU exits,
# to avoid unnecessarily flushing data to the backing file. Note
# that ``discard-data`` is only an optimization, and QEMU might
@@ -655,6 +659,7 @@
{ 'struct': 'MemoryBackendFileProperties',
'base': 'MemoryBackendProperties',
'data': { '*align': 'size',
+ '*offset': 'size',
'*discard-data': 'bool',
'mem-path': 'str',
'*pmem': { 'type': 'bool', 'if': 'CONFIG_LIBPMEM' },
diff --git a/qemu-options.hx b/qemu-options.hx
index 59bdf67a2c..701cf39feb 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4859,7 +4859,7 @@ SRST
they are specified. Note that the 'id' property must be set. These
objects are placed in the '/objects' path.
- ``-object
memory-backend-file,id=id,size=size,mem-path=dir,share=on|off,discard-data=on|off,merge=on|off,dump=on|off,prealloc=on|off,host-nodes=host-nodes,policy=default|preferred|bind|interleave,align=align,readonly=on|off``
+ ``-object
memory-backend-file,id=id,size=size,mem-path=dir,share=on|off,discard-data=on|off,merge=on|off,dump=on|off,prealloc=on|off,host-nodes=host-nodes,policy=default|preferred|bind|interleave,align=align,offset=offset,readonly=on|off``
Creates a memory file backend object, which can be used to back
the guest RAM with huge pages.
@@ -4929,6 +4929,10 @@ SRST
such cases, users can specify the required alignment via this
option.
+ The ``offset`` option specifies the offset into the target file
+ that the region starts at. You can use this parameter to overload
+ multiple regions into a single file.
+
The ``pmem`` option specifies whether the backing file specified
by ``mem-path`` is in host persistent memory that can be
accessed using the SNIA NVM programming model (e.g. Intel
diff --git a/softmmu/memory.c b/softmmu/memory.c
index 5305aca7ca..9f620085a0 100644
--- a/softmmu/memory.c
+++ b/softmmu/memory.c
@@ -1601,6 +1601,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
uint64_t align,
uint32_t ram_flags,
const char *path,
+ ram_addr_t offset,
bool readonly,
Error **errp)
{
@@ -1612,7 +1613,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
mr->destructor = memory_region_destructor_ram;
mr->align = align;
mr->ram_block = qemu_ram_alloc_from_file(size, mr, ram_flags, path,
- readonly, &err);
+ offset, readonly, &err);
if (err) {
mr->size = int128_zero();
object_unparent(OBJECT(mr));
diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index e35061bba4..829c508b3b 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -1369,6 +1369,11 @@ static void *file_ram_alloc(RAMBlock *block,
error_setg(errp, "alignment 0x%" PRIx64
" must be a power of two", block->mr->align);
return NULL;
+ } else if (offset % block->page_size) {
+ error_setg(errp, "offset 0x%" PRIx64
+ " must be multiples of page size 0x%zx",
+ offset, block->page_size);
+ return NULL;
}
block->mr->align = MAX(block->page_size, block->mr->align);
#if defined(__s390x__)
@@ -1400,7 +1405,7 @@ static void *file_ram_alloc(RAMBlock *block,
* those labels. Therefore, extending the non-empty backend file
* is disabled as well.
*/
- if (truncate && ftruncate(fd, memory)) {
+ if (truncate && ftruncate(fd, offset + memory)) {
perror("ftruncate");
}
@@ -1889,7 +1894,7 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size,
MemoryRegion *mr,
size = HOST_PAGE_ALIGN(size);
file_size = get_file_size(fd);
- if (file_size > 0 && file_size < size) {
+ if (file_size > offset && file_size < (offset + size)) {
error_setg(errp, "backing store size 0x%" PRIx64
" does not match 'size' option 0x" RAM_ADDR_FMT,
file_size, size);
@@ -1929,7 +1934,7 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size,
MemoryRegion *mr,
RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
uint32_t ram_flags, const char *mem_path,
- bool readonly, Error **errp)
+ off_t offset, bool readonly, Error **errp)
{
int fd;
bool created;
@@ -1941,7 +1946,8 @@ RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size,
MemoryRegion *mr,
return NULL;
}
- block = qemu_ram_alloc_from_fd(size, mr, ram_flags, fd, 0, readonly, errp);
+ block = qemu_ram_alloc_from_fd(size, mr, ram_flags, fd, offset, readonly,
+ errp);
if (!block) {
if (created) {
unlink(mem_path);
--
2.32.0
Amazon Development Center Germany GmbH
Krausenstr. 38
10117 Berlin
Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss
Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B
Sitz: Berlin
Ust-ID: DE 289 237 879
