From 853a059b7b4a2173997c40d9c4f098943d1b2c18 Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Tue, 3 Sep 2024 22:19:45 -0400
Subject: kernel: dev: Introduce DCDR framework

Added the Drive Cache Descriptor Ring (DCDR) framework to manage the
caching of logical blocks for LBA-based storage mediums. This commit
implements core components including data structures for Drive Cache
Descriptors (DCDs) and Drive Cache Descriptor Rings (DCDRs). Other
implemented features include:

- DCD eviction policy based on least hit count
- DCD invalidation
- DCD lookups
- Support for logical block coalescing

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 sys/include/dev/dcdr/cache.h | 85 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 85 insertions(+)
 create mode 100644 sys/include/dev/dcdr/cache.h

(limited to 'sys/include/dev/dcdr/cache.h')

diff --git a/sys/include/dev/dcdr/cache.h b/sys/include/dev/dcdr/cache.h
new file mode 100644
index 0000000..cb35103
--- /dev/null
+++ b/sys/include/dev/dcdr/cache.h
@@ -0,0 +1,85 @@
+/*
+ * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _DCDR_CACHE_H_
+#define _DCDR_CACHE_H_
+
+#include <sys/types.h>
+
+/*
+ * A drive cache descriptor (DCD) describes a logical
+ * block within a storage medium and is chained with
+ * other DCDs. Logical block coalescing is a method
+ * to optimize caching by combining adjacent logical block
+ * pairs that are infrequently invalidated into a single
+ * DCD.
+ *
+ * If the lbc bit is set, this block is coalesced with
+ * the next.
+ */
+struct dcd {
+    off_t lba;          /* Starting LBA */
+    void *data;         /* Driver specific data */
+    void *block;        /* Cached data from described block */
+    uint8_t lbc : 1;    /* Set if coalesced */
+    uint32_t hit_count; /* Number of hits */
+    struct dcd *next;   /* Next ptr for DCD chaining */
+    struct dcd *prev;   /* Prev ptr for DCD chaining */
+};
+
+/*
+ * This structure describes a drive cache descriptor
+ * ring and contains basic information like the size
+ * of each block.
+ */
+struct dcdr {
+    size_t bsize;       /* Block size */
+    size_t cap;         /* Capacity (in entries) */
+    size_t size;        /* Size (in entries) */
+    struct dcd *head;   /* Ring head */
+    struct dcd *tail;   /* Ring tail */
+};
+
+/*
+ * Result from DCDR lookup.
+ */
+struct dcdr_lookup {
+    struct dcd *dcd_res;
+    void *buf;
+    off_t lba;
+};
+
+struct dcdr *dcdr_alloc(size_t bsize, size_t cap);
+struct dcd *dcdr_cachein(struct dcdr *dcdr, void *block, off_t lba);
+
+struct dcd *dcdr_lbc_cachein(struct dcdr *dcdr, void *block, off_t lba);
+int dcdr_lookup(struct dcdr *dcdr, off_t lba, struct dcdr_lookup *res);
+int dcdr_invldcd(struct dcdr *dcdr, off_t lba);
+
+#endif  /* !_DCDR_CACHE_H_ */
-- 
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