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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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1
hw/virtio/vhost-user.c
View file

@ -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;
}