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From: Zhao Liu <zhao1.liu@intel.com>
To: "Paolo Bonzini" <pbonzini@redhat.com>,
	"Peter Xu" <peterx@redhat.com>,
	"David Hildenbrand" <david@redhat.com>,
	"Philippe Mathieu-Daudé" <philmd@linaro.org>,
	"Manos Pitsidianakis" <manos.pitsidianakis@linaro.org>,
	"Alex Bennée" <alex.bennee@linaro.org>,
	"Thomas Huth" <thuth@redhat.com>,
	"Junjie Mao" <junjie.mao@hotmail.com>
Cc: qemu-devel@nongnu.org, qemu-rust@nongnu.org,
	Dapeng Mi <dapeng1.mi@linux.intel.com>,
	Chuanxiao Dong <chuanxiao.dong@intel.com>,
	Zhao Liu <zhao1.liu@intel.com>
Subject: [RFC 14/26] memory: Expose interfaces about Flatview reference count to Rust side
Date: Thu,  7 Aug 2025 20:30:15 +0800	[thread overview]
Message-ID: <20250807123027.2910950-15-zhao1.liu@intel.com> (raw)
In-Reply-To: <20250807123027.2910950-1-zhao1.liu@intel.com>

Expose the following interfaces in include/system/memory.h without
`inline`:

* address_space_to_flatview
* flatview_ref
* flatview_unref

Then Rust side could generate related bindings.

In addtion, add documentations for these 3 interface.

Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
---
 include/system/memory.h  | 69 +++++++++++++++++++++++++++++++++++++---
 system/memory-internal.h |  1 -
 system/memory.c          |  7 +++-
 3 files changed, 71 insertions(+), 6 deletions(-)

diff --git a/include/system/memory.h b/include/system/memory.h
index e2cd6ed12614..4b9a2f528d86 100644
--- a/include/system/memory.h
+++ b/include/system/memory.h
@@ -1203,10 +1203,71 @@ struct FlatView {
     MemoryRegion *root;
 };
 
-static inline FlatView *address_space_to_flatview(AddressSpace *as)
-{
-    return qatomic_rcu_read(&as->current_map);
-}
+/**
+ * address_space_to_flatview: Get a transient RCU-protected pointer to
+ * the current FlatView.
+ *
+ * @as: The #AddressSpace to be accessed.
+ *
+ * This function retrieves a pointer to the current #FlatView for the
+ * given #AddressSpace.
+ *
+ * Note: This is a low-level, RCU-based accessor. It DOES NOT increment
+ * the FlatView's reference count. The returned pointer is only
+ * guaranteed to be valid within an RCU read-side critical section.
+ *
+ * Difference from address_space_get_flatview():
+ *
+ * For address_space_to_flatview() (this function), it is a lightweight
+ * "peek" operation. It is fast but unsafe for long-term use. Use it
+ * only for very short-lived access where performance is critical.
+ *
+ * For address_space_get_flatview(), it acquires a "strong" reference
+ * by safely incrementing the reference count. The returned pointer is
+ * stable and can be used for long-lived operations, even outside an
+ * RCU lock. It is the safer and generally preferred method, but it
+ * MUST be paired with a call to flatview_unref() after the use of
+ * #FlatView.
+ *
+ * Returns:
+ * A transient pointer to the current #FlatView, valid only under RCU
+ * protection.
+ */
+FlatView *address_space_to_flatview(AddressSpace *as);
+
+/**
+ * flatview_ref: Atomically increment the reference count of #FlatView.
+ *
+ * @view: The #FlatView whose reference count is to be incremented.
+ *
+ * This function attempts to atomically increment the reference count
+ * of the given @view. This operation is conditional and will only
+ * succeed if the current reference count is non-zero.
+ *
+ * A non-zero reference count indicates that the FlatView is live and
+ * in use. If the reference count is already zero, it indicates that the
+ * FlatView is being deinitialized, and no new references can be
+ * acquired.
+ *
+ * Returns:
+ * 'true' if the reference count was successfully incremented (i.e., it
+ * was non-zero before the call).
+ * 'false' if the reference count was already zero and could not be
+ * incremented.
+ */
+bool flatview_ref(FlatView *view);
+
+/**
+ * flatview_unref: Atomically decrement the reference count of
+ * #FlatView.
+ *
+ * @view: The #FlatView to be unreferenced.
+ *
+ * This function atomically decrements the reference count of the given
+ * @view. When the reference count drops to zero, #FlatView will be
+ * destroied via RCU.
+ */
+void flatview_unref(FlatView *view);
 
 /**
  * typedef flatview_cb: callback for flatview_for_each_range()
diff --git a/system/memory-internal.h b/system/memory-internal.h
index 46f758fa7e47..b0870a6359c3 100644
--- a/system/memory-internal.h
+++ b/system/memory-internal.h
@@ -26,7 +26,6 @@ static inline AddressSpaceDispatch *address_space_to_dispatch(AddressSpace *as)
 }
 
 FlatView *address_space_get_flatview(AddressSpace *as);
-void flatview_unref(FlatView *view);
 
 extern const MemoryRegionOps unassigned_mem_ops;
 
diff --git a/system/memory.c b/system/memory.c
index 56465479406f..2a749081fb50 100644
--- a/system/memory.c
+++ b/system/memory.c
@@ -304,7 +304,7 @@ static void flatview_destroy(FlatView *view)
     g_free(view);
 }
 
-static bool flatview_ref(FlatView *view)
+bool flatview_ref(FlatView *view)
 {
     return qatomic_fetch_inc_nonzero(&view->ref) > 0;
 }
@@ -818,6 +818,11 @@ static void address_space_add_del_ioeventfds(AddressSpace *as,
     }
 }
 
+FlatView *address_space_to_flatview(AddressSpace *as)
+{
+    return qatomic_rcu_read(&as->current_map);
+}
+
 FlatView *address_space_get_flatview(AddressSpace *as)
 {
     FlatView *view;
-- 
2.34.1



  parent reply	other threads:[~2025-08-07 12:18 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-08-07 12:30 [RFC 00/26] rust/memory: Integrate the vm-memory API from rust-vmm Zhao Liu
2025-08-07 12:30 ` [RFC 01/26] rust/hpet: Fix the error caused by vm-memory Zhao Liu
2025-08-07 13:52   ` Paolo Bonzini
2025-08-08  7:27     ` Zhao Liu
2025-08-07 12:30 ` [RFC 02/26] rust/cargo: Add the support for vm-memory Zhao Liu
2025-08-07 12:30 ` [RFC 03/26] subprojects: Add thiserror-impl crate Zhao Liu
2025-08-07 12:30 ` [RFC 04/26] subprojects: Add thiserror crate Zhao Liu
2025-08-07 12:30 ` [RFC 05/26] subprojects: Add winapi-i686-pc-windows-gnu crate Zhao Liu
2025-08-07 12:30 ` [RFC 06/26] subprojects: Add winapi-x86_64-pc-windows-gnu crate Zhao Liu
2025-08-07 12:30 ` [RFC 07/26] subprojects: Add winapi crate Zhao Liu
2025-08-07 13:17   ` Paolo Bonzini
2025-08-08  7:33     ` Zhao Liu
2025-08-07 12:30 ` [RFC 08/26] subprojects: Add vm-memory crate Zhao Liu
2025-08-07 12:30 ` [RFC 09/26] rust: Add vm-memory in meson Zhao Liu
2025-08-07 12:30 ` [RFC 10/26] subprojects/vm-memory: Patch vm-memory for QEMU memory backend Zhao Liu
2025-08-07 13:59   ` Paolo Bonzini
2025-08-08  8:17     ` Zhao Liu
2025-08-08  8:17       ` Paolo Bonzini
2025-08-08  8:51         ` Zhao Liu
2025-08-07 12:30 ` [RFC 11/26] rust/cargo: Specify the patched vm-memory crate Zhao Liu
2025-08-07 12:30 ` [RFC 12/26] rcu: Make rcu_read_lock & rcu_read_unlock not inline Zhao Liu
2025-08-07 13:54   ` Paolo Bonzini
2025-08-08  8:19     ` Zhao Liu
2025-08-07 12:30 ` [RFC 13/26] rust: Add RCU bindings Zhao Liu
2025-08-07 12:29   ` Manos Pitsidianakis
2025-08-07 13:38     ` Paolo Bonzini
2025-08-09  7:21       ` Zhao Liu
2025-08-09  9:13         ` Paolo Bonzini
2025-08-09  9:26           ` Manos Pitsidianakis
2025-08-12 10:43             ` Zhao Liu
2025-08-12 10:31       ` Zhao Liu
2025-08-07 12:30 ` Zhao Liu [this message]
2025-08-07 12:30 ` [RFC 15/26] memory: Rename address_space_lookup_region and expose it to Rust side Zhao Liu
2025-08-07 12:30 ` [RFC 16/26] memory: Make flatview_do_translate() return a pointer to MemoryRegionSection Zhao Liu
2025-08-07 13:57   ` Paolo Bonzini
2025-08-12 15:39     ` Zhao Liu
2025-08-12 15:42       ` Manos Pitsidianakis
2025-08-13 15:12         ` Zhao Liu
2025-08-12 19:23       ` Paolo Bonzini
2025-08-13 15:10         ` Zhao Liu
2025-08-07 12:30 ` [RFC 17/26] memory: Add a translation helper to return MemoryRegionSection Zhao Liu
2025-08-07 12:30 ` [RFC 18/26] memory: Rename flatview_access_allowed() to memory_region_access_allowed() Zhao Liu
2025-08-07 12:41   ` Manos Pitsidianakis
2025-08-07 12:30 ` [RFC 19/26] memory: Add MemoryRegionSection based misc helpers Zhao Liu
2025-08-07 12:30 ` [RFC 20/26] memory: Add wrappers of intermediate steps for read/write Zhao Liu
2025-08-07 12:30 ` [RFC 21/26] memory: Add store/load interfaces for Rust side Zhao Liu
2025-08-07 12:30 ` [RFC 22/26] rust/memory: Implement vm_memory::GuestMemoryRegion for MemoryRegionSection Zhao Liu
2025-08-07 12:30 ` [RFC 23/26] rust/memory: Implement vm_memory::GuestMemory for FlatView Zhao Liu
2025-08-07 12:30 ` [RFC 24/26] rust/memory: Provide AddressSpace bindings Zhao Liu
2025-08-07 13:50   ` Paolo Bonzini
2025-08-13 14:47     ` Zhao Liu
2025-08-07 12:30 ` [RFC 25/26] rust/memory: Add binding to check target endian Zhao Liu
2025-08-07 12:44   ` Manos Pitsidianakis
2025-08-13 14:48     ` Zhao Liu
2025-08-07 12:30 ` [RFC 26/26] rust/hpet: Use safe binding to access address space Zhao Liu
2025-08-07 12:42 ` [RFC 00/26] rust/memory: Integrate the vm-memory API from rust-vmm Zhao Liu
2025-08-07 14:13 ` Paolo Bonzini
2025-08-13 14:56   ` Zhao Liu

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