* [GIT PULL 1/1] hostmem-file: add offset option
2023-05-23 15:02 [GIT PULL 0/1] Host Memory Backends and Memory devices queue 2023-05-23 David Hildenbrand
@ 2023-05-23 15:02 ` David Hildenbrand
2023-05-23 20:06 ` [GIT PULL 0/1] Host Memory Backends and Memory devices queue 2023-05-23 Richard Henderson
1 sibling, 0 replies; 3+ messages in thread
From: David Hildenbrand @ 2023-05-23 15:02 UTC (permalink / raw)
To: qemu-devel
Cc: Alexander Graf, Markus Armbruster, Peter Xu, Igor Mammedov,
Michael S . Tsirkin, Paolo Bonzini, Peter Maydell,
David Hildenbrand
From: Alexander Graf <graf@amazon.com>
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>
---
backends/hostmem-file.c | 40 +++++++++++++++++++++++++++++++++++++++-
hw/virtio/vhost-user.c | 1 +
include/exec/memory.h | 2 ++
include/exec/ram_addr.h | 3 ++-
include/exec/ramblock.h | 1 +
qapi/qom.json | 5 +++++
qemu-options.hx | 6 +++++-
softmmu/memory.c | 3 ++-
softmmu/physmem.c | 17 ++++++++++++-----
9 files changed, 69 insertions(+), 9 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/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index e3ec8727da..74a2a28663 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -473,6 +473,7 @@ static MemoryRegion *vhost_user_get_mr_data(uint64_t addr, ram_addr_t *offset,
assert((uintptr_t)addr == addr);
mr = memory_region_from_host((void *)(uintptr_t)addr, offset);
*fd = memory_region_get_fd(mr);
+ *offset += mr->ram_block->fd_offset;
return mr;
}
diff --git a/include/exec/memory.h b/include/exec/memory.h
index 6f24a3dd46..c3661b2276 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -1326,6 +1326,7 @@ 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.
*
@@ -1339,6 +1340,7 @@ 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/include/exec/ramblock.h b/include/exec/ramblock.h
index adc03df59c..69c6a53902 100644
--- a/include/exec/ramblock.h
+++ b/include/exec/ramblock.h
@@ -40,6 +40,7 @@ struct RAMBlock {
QLIST_ENTRY(RAMBlock) next;
QLIST_HEAD(, RAMBlockNotifier) ramblock_notifiers;
int fd;
+ uint64_t fd_offset;
size_t page_size;
/* dirty bitmap used during migration */
unsigned long *bmap;
diff --git a/qapi/qom.json b/qapi/qom.json
index f61badaba4..7f92ea43e8 100644
--- a/qapi/qom.json
+++ b/qapi/qom.json
@@ -647,6 +647,10 @@
# 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 back multiple regions with a single file. Must
+# be a multiple of the page size. (default: 0) (since 8.1)
+#
# @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
@@ -668,6 +672,7 @@
{ '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 e4566149ee..b37eb9662b 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4949,7 +4949,7 @@ 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.
@@ -5019,6 +5019,10 @@ 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 back
+ multiple regions with 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 9ee4131d75..7d9494ce70 100644
--- a/softmmu/memory.c
+++ b/softmmu/memory.c
@@ -1619,6 +1619,7 @@ 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)
{
@@ -1630,7 +1631,7 @@ 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 efaed36773..9d7e172260 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");
}
@@ -1416,6 +1421,7 @@ static void *file_ram_alloc(RAMBlock *block,
}
block->fd = fd;
+ block->fd_offset = offset;
return area;
}
#endif
@@ -1889,7 +1895,7 @@ 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 +1935,7 @@ 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 +1947,8 @@ 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);
@@ -2075,7 +2082,7 @@ void qemu_ram_remap(ram_addr_t addr, ram_addr_t length)
flags |= block->flags & RAM_NORESERVE ? MAP_NORESERVE : 0;
if (block->fd >= 0) {
area = mmap(vaddr, length, PROT_READ | PROT_WRITE,
- flags, block->fd, offset);
+ flags, block->fd, offset + block->fd_offset);
} else {
flags |= MAP_ANONYMOUS;
area = mmap(vaddr, length, PROT_READ | PROT_WRITE,
--
2.40.1
^ permalink raw reply related [flat|nested] 3+ messages in thread