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>

2 files changed, 330 insertions, 0 deletions

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_ */