[PATCH v3 2/3] memory: add memory_region_is_mapped_shared()

[Stefan Hajnoczi <stefanha@redhat.com>]

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 <stefanha@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 c3d417d317..5976f05a01 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -2763,6 +2763,17 @@ 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 bfedaf9c4d..3c4510c809 100644
--- a/softmmu/memory.c
+++ b/softmmu/memory.c
@@ -1811,6 +1811,12 @@ 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) &&
+           (mr->ram_block->flags & RAM_SHARED);
+}
+
 uint8_t memory_region_get_dirty_log_mask(MemoryRegion *mr)
 {
     uint8_t mask = mr->dirty_log_mask;
-- 
2.31.1