From 7b0701707857a3205cbd4fc69c08429a193c5bff Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Sat, 16 Aug 2025 20:23:15 -0400
Subject: kernel: disk: Introduce virtual blocks

This commit implements the concept of virtual blocks which may be bigger
than the hardware block size (e.g., 512 bytes). The virtual block size
must be a multiple of the hardware blocksize. The system will panic if
this condition is not met.

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 sys/include/sys/disk.h | 24 ++++++++++++++++++++++++
 sys/kern/kern_disk.c   | 14 ++++++++++++--
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/sys/include/sys/disk.h b/sys/include/sys/disk.h
index f6ed126..e503e21 100644
--- a/sys/include/sys/disk.h
+++ b/sys/include/sys/disk.h
@@ -33,9 +33,33 @@
 #include <sys/syscall.h>
 #include <sys/queue.h>
 #include <sys/device.h>
+#include <sys/cdefs.h>
 #include <sys/types.h>
 #include <sys/limits.h>
 #include <sys/cdefs.h>
+#if defined(_KERNEL)
+#include <dev/dcdr/cache.h>
+#endif  /* _KERNEL */
+
+/*
+ * V_BSIZE is the virtual block size in bytes used
+ * by the disk framework. The virtual block size is a
+ * multiple of the hardware block size and defines
+ * how many bytes a virtual block is made up of.
+ *
+ * A virtual block is simply a unit specific to
+ * the disk framework that represents multiple
+ * hardware disk blocks.
+ */
+#if defined(__V_BSIZE)
+#define V_BSIZE __V_BSIZE
+#else
+#define V_BSIZE 4096
+#endif  /* __V_BSIZE */
+
+/* Sanitize the silly human's input */
+_Static_assert(V_BSIZE > 512, "V_BSIZE must be > 512");
+_Static_assert((V_BSIZE & 1) == 0, "V_BSIZE must be a power of two");
 
 #define DISK_PRIMARY 0  /* ID of primary disk */
 
diff --git a/sys/kern/kern_disk.c b/sys/kern/kern_disk.c
index b956c02..af2aa13 100644
--- a/sys/kern/kern_disk.c
+++ b/sys/kern/kern_disk.c
@@ -171,6 +171,10 @@ __disk_get_id(diskid_t id)
  * @buf: Buffer to read data into
  * @len: Number of bytes to read
  * @write: If true, do a write
+ *
+ * XXX: The size in which blocks are read at is in
+ *      virtual blocks which is defined by V_BSIZE
+ *      in sys/disk.h
  */
 static ssize_t
 disk_rw(diskid_t id, blkoff_t blk, void *buf, size_t len, bool write)
@@ -180,6 +184,8 @@ disk_rw(diskid_t id, blkoff_t blk, void *buf, size_t len, bool write)
     struct disk *dp;
     int error;
 
+    len = ALIGN_UP(len, V_BSIZE);
+
     /* Attempt to grab the disk object */
     error = disk_get_id(id, &dp);
     if (error < 0) {
@@ -268,6 +274,10 @@ disk_add(const char *name, dev_t dev, const struct bdevsw *bdev, int flags)
     dp->id = disk_count++;
     dp->bsize = DEFAULT_BSIZE;
 
+    if ((V_BSIZE & (dp->bsize - 1)) != 0) {
+        panic("virtual block size not hw bsize aligned\n");
+    }
+
     /* Now we can add it to the queue */
     spinlock_acquire(&diskq_lock);
     TAILQ_INSERT_TAIL(&diskq, dp, link);
@@ -343,9 +353,9 @@ disk_buf_alloc(diskid_t id, size_t len)
 
     /*
      * Here we will align the buffer size by the
-     * disk's block size to ensure it is big enough.
+     * virtual block size to ensure it is big enough.
      */
-    len = ALIGN_UP(len, dp->bsize);
+    len = ALIGN_UP(len, V_BSIZE);
     buf = dynalloc(len);
     return buf;
 }
-- 
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