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/dev/dcdr/cache.c | 245 +++++++++++++++++++++++++++++++++++++++++++
sys/include/dev/dcdr/cache.h | 85 +++++++++++++++
2 files changed, 330 insertions(+)
create mode 100644 sys/dev/dcdr/cache.c
create mode 100644 sys/include/dev/dcdr/cache.h
(limited to 'sys')
diff --git a/sys/dev/dcdr/cache.c b/sys/dev/dcdr/cache.c
new file mode 100644
index 0000000..e13c9c7
--- /dev/null
+++ b/sys/dev/dcdr/cache.c
@@ -0,0 +1,245 @@
+/*
+ * 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.
+ */
+
+#include <sys/types.h>
+#include <dev/dcdr/cache.h>
+#include <vm/dynalloc.h>
+#include <string.h>
+
+/*
+ * Remove a DCD from a DCDR.
+ */
+static void
+dcdr_remove(struct dcdr *dcdr, struct dcd *dcd)
+{
+ /* Handle the head being invalidated */
+ if (dcd == dcdr->head) {
+ dcdr->head = dcd->next;
+ return;
+ }
+
+ /* Handle the tail being invalidated */
+ if (dcd == dcdr->tail) {
+ dcdr->tail = dcd->prev;
+ return;
+ }
+
+ if (dcd->prev != NULL) {
+ dcd->prev->next = dcd->next;
+ }
+
+ if (dcd->next != NULL) {
+ dcd->next->prev = dcd->prev;
+ }
+
+ if (dcdr->size > 0) {
+ --dcdr->size;
+ }
+}
+
+/*
+ * Evict a DCD with the lowest hit count
+ * from a DCDR.
+ */
+static void
+dcdr_evict_least(struct dcdr *dcdr)
+{
+ struct dcd *tmp = dcdr->head;
+ struct dcd *cnp = NULL; /* Candidate */
+
+ /* Find DCD eviction candidate */
+ while (tmp != NULL) {
+ if (cnp == NULL) {
+ cnp = tmp;
+ continue;
+ }
+
+ if (tmp->hit_count < cnp->hit_count) {
+ cnp = tmp;
+ }
+
+ tmp = tmp->next;
+ }
+
+ /* Invalidate DCD found if any */
+ if (cnp != NULL) {
+ dcdr_invldcd(dcdr, cnp->lba);
+ }
+}
+
+/*
+ * Allocates a DCDR structure using a
+ * specific block size.
+ *
+ * Returns NULL on failure.
+ */
+struct dcdr *
+dcdr_alloc(size_t bsize, size_t cap)
+{
+ struct dcdr *tmp;
+
+ tmp = dynalloc(sizeof(*tmp));
+ if (tmp == NULL) {
+ return NULL;
+ }
+
+ tmp->bsize = bsize;
+ tmp->head = NULL;
+ tmp->tail = NULL;
+ tmp->cap = cap;
+ tmp->size = 0;
+ return tmp;
+}
+
+/*
+ * Cache a logical block and return a DCD that
+ * describes it. This will allocate a block and
+ * copy `block` to the allocated memory.
+ */
+struct dcd *
+dcdr_cachein(struct dcdr *dcdr, void *block, off_t lba)
+{
+ struct dcd *dcd, *tmp;
+
+ dcd = dynalloc(sizeof(*dcd));
+ if (dcd == NULL) {
+ return NULL;
+ }
+
+ memset(dcd, 0, sizeof(*dcd));
+ dcd->block = dynalloc(dcdr->bsize);
+ if (dcd->block == NULL) {
+ dynfree(dcd);
+ return NULL;
+ }
+
+ dcd->lba = lba;
+ dcd->next = NULL;
+ dcd->hit_count = 0;
+ memcpy(block, dcd->block, dcdr->bsize);
+
+ /*
+ * If we've hit the capacity of the DCDR then
+ * we will need to evict some DCD to make room
+ * for this new one.
+ */
+ if (dcdr->size >= dcdr->cap) {
+ dcdr_evict_least(dcdr);
+ }
+
+ /* Insert DCD into DCDR */
+ if (dcdr->head == NULL) {
+ dcdr->head = dcd;
+ dcdr->tail = dcd;
+ } else {
+ tmp = dcdr->tail;
+ dcd->prev = tmp;
+ tmp->next = dcd;
+ dcdr->tail = dcd;
+ }
+
+ ++dcdr->size;
+ return dcd;
+}
+
+/*
+ * Cache two consecutive logical blocks and
+ * return the DCD describing the first.
+ *
+ * XXX: 'block' *must* span two LBAs
+ */
+struct dcd *
+dcdr_lbc_cachein(struct dcdr *dcdr, void *block, off_t lba)
+{
+ struct dcd *tmp;
+
+ tmp = dcdr_cachein(dcdr, block, lba);
+ dcdr_cachein(dcdr, (char *)block + dcdr->bsize, lba);
+ tmp->lbc = 1;
+ return tmp;
+}
+
+/*
+ * Search for a logical block within the cache.
+ *
+ * Returns 0 upon a cache hit with "res" being set
+ * and returns a less than 0 value upon a cache miss.
+ */
+int
+dcdr_lookup(struct dcdr *dcdr, off_t lba, struct dcdr_lookup *res)
+{
+ struct dcdr_lookup ret;
+ struct dcd *tmp = dcdr->head;
+
+ while (tmp != NULL) {
+ if (tmp->lba == lba) {
+ ++tmp->hit_count;
+ ret.dcd_res = tmp;
+ ret.lba = lba;
+ ret.buf = tmp->block;
+ *res = ret;
+ return 0;
+ }
+
+ if (tmp->lbc && tmp->lba == (lba - 1)) {
+ ++tmp->hit_count;
+ ret.dcd_res = tmp;
+ ret.lba = lba;
+ ret.buf = (char *)tmp->block + dcdr->bsize;
+ *res = ret;
+ return 0;
+ }
+
+ tmp = tmp->next;
+ }
+
+ return -1;
+}
+
+/*
+ * Invalidate a DCD within a DCDR.
+ */
+int
+dcdr_invldcd(struct dcdr *dcdr, off_t lba)
+{
+ struct dcdr_lookup tmp;
+ struct dcd *dcd;
+ int error;
+
+ if ((error = dcdr_lookup(dcdr, lba, &tmp)) < 0) {
+ return error;
+ }
+
+ dcd = tmp.dcd_res;
+ dcdr_remove(dcdr, dcd);
+
+ dynfree(dcd->block);
+ dynfree(dcd);
+ return 0;
+}
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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