ref: 91f46286cc54a2c7a327feb10eec830b41089ecc
parent: e6634c060580c04c0b1dd4bbf90a175e5e43f835
author: ngkaho1234 <ngkaho1234@gmail.com>
date: Mon Nov 23 09:28:09 EST 2015
ext4_bcache: add comments to the changes.
--- a/lwext4/ext4_bcache.c
+++ b/lwext4/ext4_bcache.c
@@ -82,6 +82,25 @@
return EOK;
}
+/**@brief:
+ *
+ * This is ext4_bcache, the module handling basic buffer-cache stuff.
+ *
+ * Buffers in a bcache are sorted by their LBA and stored in a
+ * RB-Tree(lba_root).
+ *
+ * Bcache also maintains another RB-Tree(lru_root) right now, where
+ * buffers are sorted by their LRU id.
+ *
+ * A singly-linked list is used to track those dirty buffers which are
+ * ready to be flushed. (Those buffers which are dirty but also referenced
+ * are not considered ready to be flushed.)
+ *
+ * When a buffer is not referenced, it will be stored in both lba_root
+ * and lru_root, while it will only be stored in lba_root when it is
+ * referenced.
+ */
+
static struct ext4_buf *
ext4_buf_alloc(struct ext4_bcache *bc, uint64_t lba)
{@@ -151,9 +170,13 @@
int ext4_bcache_alloc(struct ext4_bcache *bc, struct ext4_block *b,
bool *is_new)
{+ /* Try to search the buffer with exaxt LBA. */
struct ext4_buf *buf = ext4_buf_lookup(bc, b->lb_id);
if (buf) {+ /* If buffer is not referenced. */
if (!buf->refctr) {+ /* Assign new value to LRU id and increment LRU counter
+ * by 1*/
buf->lru_id = ++bc->lru_ctr;
RB_REMOVE(ext4_buf_lru, &bc->lru_root, buf);
if (ext4_bcache_test_flag(buf, BC_DIRTY))
@@ -165,26 +188,37 @@
}
buf->refctr++;
+
b->uptodate = ext4_bcache_test_flag(buf, BC_UPTODATE);
+ /* Right now we don't propagate the dirty flag from ext4_buf to
+ * ext4_block. */
b->dirty = false;
b->buf = buf;
b->data = buf->data;
+
*is_new = false;
return EOK;
}
+
+ /* We need to allocate one buffer.*/
buf = ext4_buf_alloc(bc, b->lb_id);
if (!buf)
return ENOMEM;
RB_INSERT(ext4_buf_lba, &bc->lba_root, buf);
+ /* One more buffer in bcache now. :-) */
bc->ref_blocks++;
buf->refctr = 1;
+ /* Assign new value to LRU id and increment LRU counter
+ * by 1*/
buf->lru_id = ++bc->lru_ctr;
+
b->uptodate = false;
b->dirty = false;
b->buf = buf;
b->data = buf->data;
+
*is_new = true;
return EOK;
}
@@ -208,22 +242,28 @@
/*Just decrease reference counter*/
buf->refctr--;
+ /* TODO: it looks useless... */
if (free_delay)
bc->free_delay = free_delay;
+ /* If buffer is modified, buf will be mark up-to-date and dirty. */
if (b->dirty) {ext4_bcache_set_flag(buf, BC_DIRTY);
ext4_bcache_set_flag(buf, BC_UPTODATE);
b->uptodate = true;
}
+ /* Someone might want to drop this buffer from bcache. */
if (!b->uptodate)
ext4_bcache_clear_flag(buf, BC_UPTODATE);
+ /* We are the last one touching this buffer, do the cleanups. */
if (!buf->refctr) {RB_INSERT(ext4_buf_lru, &bc->lru_root, buf);
+ /* This buffer is ready to be flushed. */
if (ext4_bcache_test_flag(buf, BC_DIRTY))
SLIST_INSERT_HEAD(&bc->dirty_list, buf, dirty_node);
+ /* The buffer is invalidated...drop it. */
if (!ext4_bcache_test_flag(buf, BC_UPTODATE))
ext4_bcache_drop_buf(bc, buf);
--- a/lwext4/ext4_blockdev.c
+++ b/lwext4/ext4_blockdev.c
@@ -92,6 +92,7 @@
struct ext4_bcache *bc = bdev->bc;
/*Only flushing unreferenced buffer is allowed.*/
ext4_assert(!buf->refctr);
+
if (ext4_bcache_test_flag(buf, BC_DIRTY)) {r = ext4_blocks_set_direct(bdev, buf->data, buf->lba, 1);
if (r)