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// SPDX-License-Identifier: GPL-2.0-or-later
/*
* Copyright (C) 2026 Richard QIn
*/
#include "kernel/buf.h"
#include "kernel/spinlock.h"
#include "kernel/riscv.h"
#include "drivers/virtio.h"
#include "drivers/uart.h"
namespace BufferCache
{
struct
{
Spinlock lock;
struct Buf buf[NBUF];
struct Buf head;
} bcache;
void init()
{
bcache.lock.init("bcache");
// Initialize LRU doubly circular linked list
bcache.head.prev = &bcache.head;
bcache.head.next = &bcache.head;
for (struct Buf *b = bcache.buf; b < bcache.buf + NBUF; ++b)
{
b->lock.init("buffer");
b->next = bcache.head.next;
b->prev = &bcache.head;
bcache.head.next->prev = b;
bcache.head.next = b;
}
Drivers::uart_puts("[Bio] Buffer cache initialized.\n");
}
static struct Buf* bget(uint32 dev, uint32 blockno)
{
struct Buf* b;
bcache.lock.acquire();
// Attempt to hit the cache
for (b = bcache.head.next; b != &bcache.head; b = b->next)
{
if (b->dev == dev && b->blockno == blockno)
{
b->refcnt++;
bcache.lock.release();
b->lock.acquire(); // Acquire Sleep Lock
return b;
}
}
// Cache miss, evicting LRU
for (b = bcache.head.prev; b != &bcache.head; b = b->prev)
{
if (b->refcnt == 0)
{
b->dev = dev;
b->blockno = blockno;
b->valid = 0;
b->refcnt = 1;
bcache.lock.release();
b->lock.acquire();
return b;
}
}
Drivers::uart_puts("panic: bget: no buffers\n");
while (1)
;
}
struct Buf* bread(uint32 dev, uint32 blockno)
{
struct Buf *b = bget(dev, blockno);
if (!b->valid)
{
VirtIO::rw(0, b->blockno, (char *)b->data);
b->valid = 1;
}
return b;
}
void bwrite(struct Buf *b)
{
if (!b->lock.holding())
{
Drivers::uart_puts("panic: bwrite\n");
while (1)
;
}
VirtIO::rw(1, b->blockno, (char *)b->data);
}
void brelse(struct Buf *b)
{
if (!b->lock.holding())
{
Drivers::uart_puts("panic: brelse\n");
while (1)
;
}
b->lock.release();
bcache.lock.acquire();
b->refcnt--;
if (b->refcnt == 0)
{
b->next->prev = b->prev;
b->prev->next = b->next;
b->next = bcache.head.next;
b->prev = &bcache.head;
bcache.head.next->prev = b;
bcache.head.next = b;
}
bcache.lock.release();
}
void bpin(struct Buf *b)
{
bcache.lock.acquire();
b->refcnt++;
bcache.lock.release();
}
void bunpin(struct Buf* b)
{
bcache.lock.acquire();
b->refcnt --;
bcache.lock.release();
}
} // namespace BufferCache
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