[PATCH v2 3/8] ntoskrnl.exe: Implement ExAcquireResourceSharedLite().

[Zebediah Figura]

Signed-off-by: Zebediah Figura <z.figura12 at gmail.com>
---
 dlls/ntoskrnl.exe/ntoskrnl.exe.spec |  2 +-
 dlls/ntoskrnl.exe/sync.c            | 82 +++++++++++++++++++++++++++++
 include/ddk/wdm.h                   |  1 +
 3 files changed, 84 insertions(+), 1 deletion(-)

diff --git a/dlls/ntoskrnl.exe/ntoskrnl.exe.spec b/dlls/ntoskrnl.exe/ntoskrnl.exe.spec
index 508f9e650c..177800a8dc 100644
--- a/dlls/ntoskrnl.exe/ntoskrnl.exe.spec
+++ b/dlls/ntoskrnl.exe/ntoskrnl.exe.spec
@@ -121,7 +121,7 @@
 @ stdcall DbgQueryDebugFilterState(long long)
 @ stub DbgSetDebugFilterState
 @ stdcall ExAcquireResourceExclusiveLite(ptr long)
-@ stub ExAcquireResourceSharedLite
+@ stdcall ExAcquireResourceSharedLite(ptr long)
 @ stub ExAcquireSharedStarveExclusive
 @ stub ExAcquireSharedWaitForExclusive
 @ stub ExAllocateFromPagedLookasideList
diff --git a/dlls/ntoskrnl.exe/sync.c b/dlls/ntoskrnl.exe/sync.c
index 0c8d02f7dd..82667e8510 100644
--- a/dlls/ntoskrnl.exe/sync.c
+++ b/dlls/ntoskrnl.exe/sync.c
@@ -19,6 +19,7 @@
  */
 
 #include "config.h"
+#include <limits.h>
 #include <stdarg.h>
 
 #include "ntstatus.h"
@@ -742,6 +743,25 @@ NTSTATUS WINAPI ExInitializeResourceLite( ERESOURCE *resource )
     return STATUS_SUCCESS;
 }
 
+/* Find an existing entry in the shared owner list, or create a new one. */
+static OWNER_ENTRY *resource_get_shared_entry( ERESOURCE *resource, ERESOURCE_THREAD thread )
+{
+    ULONG i, count;
+
+    for (i = 0; i < resource->OwnerEntry.TableSize; ++i)
+    {
+        if (resource->OwnerTable[i].OwnerThread == thread)
+            return &resource->OwnerTable[i];
+    }
+
+    count = ++resource->OwnerEntry.TableSize;
+    resource->OwnerTable = heap_realloc(resource->OwnerTable, count * sizeof(*resource->OwnerTable));
+    resource->OwnerTable[count - 1].OwnerThread = thread;
+    resource->OwnerTable[count - 1].OwnerCount = 0;
+
+    return &resource->OwnerTable[count - 1];
+}
+
 /***********************************************************************
  *           ExAcquireResourceExclusiveLite  (NTOSKRNL.EXE.@)
  */
@@ -798,3 +818,65 @@ BOOLEAN WINAPI ExAcquireResourceExclusiveLite( ERESOURCE *resource, BOOLEAN wait
 
     return TRUE;
 }
+
+/***********************************************************************
+ *           ExAcquireResourceSharedLite  (NTOSKRNL.EXE.@)
+ */
+BOOLEAN WINAPI ExAcquireResourceSharedLite( ERESOURCE *resource, BOOLEAN wait )
+{
+    OWNER_ENTRY *entry;
+    KIRQL irql;
+
+    TRACE("resource %p, wait %u.\n", resource, wait);
+
+    KeAcquireSpinLock( &resource->SpinLock, &irql );
+
+    entry = resource_get_shared_entry( resource, (ERESOURCE_THREAD)KeGetCurrentThread() );
+
+    if (resource->Flag & ResourceOwnedExclusive)
+    {
+        if (resource->OwnerEntry.OwnerThread == (ERESOURCE_THREAD)KeGetCurrentThread())
+        {
+            /* We own the resource exclusively, so increase recursion. */
+            resource->ActiveEntries++;
+            KeReleaseSpinLock( &resource->SpinLock, irql );
+            return TRUE;
+        }
+    }
+    else if (entry->OwnerCount || !resource->NumberOfExclusiveWaiters)
+    {
+        /* Either we already own the resource shared, or there are no exclusive
+         * owners or waiters, so we can grab it shared. */
+        entry->OwnerCount++;
+        resource->ActiveEntries++;
+        KeReleaseSpinLock( &resource->SpinLock, irql );
+        return TRUE;
+    }
+
+    if (!wait)
+    {
+        KeReleaseSpinLock( &resource->SpinLock, irql );
+        return FALSE;
+    }
+
+    if (!resource->SharedWaiters)
+    {
+        resource->SharedWaiters = heap_alloc( sizeof(*resource->SharedWaiters) );
+        KeInitializeSemaphore( resource->SharedWaiters, 0, INT_MAX );
+    }
+    resource->NumberOfSharedWaiters++;
+
+    KeReleaseSpinLock( &resource->SpinLock, irql );
+
+    KeWaitForSingleObject( resource->SharedWaiters, Executive, KernelMode, FALSE, NULL );
+
+    KeAcquireSpinLock( &resource->SpinLock, &irql );
+
+    entry->OwnerCount++;
+    resource->ActiveEntries++;
+    resource->NumberOfSharedWaiters--;
+
+    KeReleaseSpinLock( &resource->SpinLock, irql );
+
+    return TRUE;
+}
diff --git a/include/ddk/wdm.h b/include/ddk/wdm.h
index 69916056eb..a153942bf5 100644
--- a/include/ddk/wdm.h
+++ b/include/ddk/wdm.h
@@ -1513,6 +1513,7 @@ static inline void IoSetCompletionRoutine(IRP *irp, PIO_COMPLETION_ROUTINE routi
 NTSTATUS  WINAPI DbgQueryDebugFilterState(ULONG, ULONG);
 void      WINAPI ExAcquireFastMutexUnsafe(PFAST_MUTEX);
 BOOLEAN   WINAPI ExAcquireResourceExclusiveLite(ERESOURCE*,BOOLEAN);
+BOOLEAN   WINAPI ExAcquireResourceSharedLite(ERESOURCE*,BOOLEAN);
 PVOID     WINAPI ExAllocatePool(POOL_TYPE,SIZE_T);
 PVOID     WINAPI ExAllocatePoolWithQuota(POOL_TYPE,SIZE_T);
 PVOID     WINAPI ExAllocatePoolWithTag(POOL_TYPE,SIZE_T,ULONG);
-- 
2.21.0