On Mon, Feb 22, 2021 at 8:11 PM Stefan Hajnoczi <stefa...@redhat.com> wrote:
> Add a function to query whether a memory region is mmap(MAP_SHARED).
> This will be used to check that vhost-user memory regions can be shared
> with the device backend process in the next patch.
>
> An inline function in "exec/memory.h" would have been nice but RAMBlock
> fields are only accessible from memory.c (see "exec/ramblock.h").
>
> Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
> ---
> include/exec/memory.h | 11 +++++++++++
> softmmu/memory.c | 6 ++++++
> 2 files changed, 17 insertions(+)
>
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index c6fb714e49..7b7dbe9fd0 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -2457,6 +2457,17 @@ static inline bool
> memory_access_is_direct(MemoryRegion *mr, bool is_write)
> }
> }
>
> +/**
> + * memory_region_is_mapped_shared: check whether a memory region is
> + * mmap(MAP_SHARED)
> + *
> + * Returns %true is a memory region is mmap(MAP_SHARED). This is always
> false
> + * on memory regions that do not support memory_region_get_ram_ptr().
> + *
> + * @mr: the memory region being queried
> + */
> +bool memory_region_is_mapped_shared(MemoryRegion *mr);
> +
> /**
> * address_space_read: read from an address space.
> *
> diff --git a/softmmu/memory.c b/softmmu/memory.c
> index 874a8fccde..e6631e5d4c 100644
> --- a/softmmu/memory.c
> +++ b/softmmu/memory.c
> @@ -1809,6 +1809,12 @@ bool memory_region_is_ram_device(MemoryRegion *mr)
> return mr->ram_device;
> }
>
> +bool memory_region_is_mapped_shared(MemoryRegion *mr)
> +{
> + return memory_access_is_direct(mr, false) &&
>
memory_access_is_direct is a bit special, it treats ram-device differently
from rom-device since commit 4a2e242bbb306 ("memory: Don't use memcpy for
ram_device regions").
I don't think it's an issue for now, but I wonder if in the future we will
share ram-device as well.
Where did you get the idea to use that function? I suppose that's also the
one we use somewhere else in the code path sharing the VM memory.
+ (mr->ram_block->flags & RAM_SHARED);
> +}
> +
> uint8_t memory_region_get_dirty_log_mask(MemoryRegion *mr)
> {
> uint8_t mask = mr->dirty_log_mask;
> --
> 2.29.2
>
>
