From 290d3478f245bb7d2112bb781286a9fbae42b983 Mon Sep 17 00:00:00 2001
From: Simon Rettberg
Date: Fri, 13 Mar 2020 16:03:29 +0100
Subject: [SERVER] Rewrite uplink queue handling

- Now uses linked lists instead of huge array
- Does prefetch data on client requests
- Can have multiple replication requests in-flight
---
 src/server/image.h | 44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

(limited to 'src/server/image.h')

diff --git a/src/server/image.h b/src/server/image.h
index 4614c74..b23711b 100644
--- a/src/server/image.h
+++ b/src/server/image.h
@@ -51,6 +51,50 @@ bool image_ensureDiskSpaceLocked(uint64_t size, bool force);
 
 bool image_saveCacheMap(dnbd3_image_t *image);
 
+/**
+ * Check if given range is cached. Be careful when using this function because:
+ * 1) you need to hold a reference to the cache map
+ * 2) start and end are assumed to be 4k aligned
+ * 3) start and end are not checked to be in bounds (we don't know the image in this context)
+ */
+static inline bool image_isRangeCachedUnsafe(dnbd3_cache_map_t *cache, uint64_t start, uint64_t end)
+{
+	const uint64_t firstByteInMap = start >> 15;
+	const uint64_t lastByteInMap = (end - 1) >> 15;
+	const uint8_t fb = (uint8_t)(0xff << ((start >> 12) & 7));
+	const uint8_t lb = (uint8_t)(~(0xff << ((((end - 1) >> 12) & 7) + 1)));
+	uint64_t pos;
+	uint8_t b;
+	bool isCached;
+	if ( firstByteInMap == lastByteInMap ) { // Single byte to check, much simpler
+		b = cache->map[firstByteInMap];
+		isCached = ( b & ( fb & lb ) ) == ( fb & lb );
+	} else {
+		isCached = true;
+		atomic_thread_fence( memory_order_acquire );
+		// First byte
+		if ( isCached ) {
+			b = atomic_load_explicit( &cache->map[firstByteInMap], memory_order_relaxed );
+			isCached = ( ( b & fb ) == fb );
+		}
+		// Last byte
+		if ( isCached ) {
+			b = atomic_load_explicit( &cache->map[lastByteInMap], memory_order_relaxed );
+			isCached = ( ( b & lb ) == lb );
+		}
+		// Middle, must be all bits set (0xff)
+		if ( isCached ) {
+			for ( pos = firstByteInMap + 1; pos < lastByteInMap; ++pos ) {
+				if ( atomic_load_explicit( &cache->map[pos], memory_order_relaxed ) != 0xff ) {
+					isCached = false;
+					break;
+				}
+			}
+		}
+	}
+	return isCached;
+}
+
 // one byte in the map covers 8 4kib blocks, so 32kib per byte
 // "+ (1 << 15) - 1" is required to account for the last bit of
 // the image that is smaller than 32kib
-- 
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