qed: Table, L2 cache, and cluster functions (298800ca) · Commits · SUMMER2020 / students / proj-2021291

Makefile.objs

+1 −1

Original line number	Diff line number	Diff line
		@@ -20,7 +20,7 @@ block-obj-$(CONFIG_LINUX_AIO) += linux-aio.o

		block-nested-y += raw.o cow.o qcow.o vdi.o vmdk.o cloop.o dmg.o bochs.o vpc.o vvfat.o
		block-nested-y += qcow2.o qcow2-refcount.o qcow2-cluster.o qcow2-snapshot.o
		block-nested-y += qed.o
		block-nested-y += qed.o qed-gencb.o qed-l2-cache.o qed-table.o qed-cluster.o
		block-nested-y += parallels.o nbd.o blkdebug.o sheepdog.o blkverify.o
		block-nested-$(CONFIG_WIN32) += raw-win32.o
		block-nested-$(CONFIG_POSIX) += raw-posix.o

block/qed-cluster.c

0 → 100644

+154 −0

Original line number	Diff line number	Diff line
		/*
		* QEMU Enhanced Disk Format Cluster functions
		*
		* Copyright IBM, Corp. 2010
		*
		* Authors:
		* Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
		* Anthony Liguori <aliguori@us.ibm.com>
		*
		* This work is licensed under the terms of the GNU LGPL, version 2 or later.
		* See the COPYING.LIB file in the top-level directory.
		*
		*/

		#include "qed.h"

		/**
		* Count the number of contiguous data clusters
		*
		* @s: QED state
		* @table: L2 table
		* @index: First cluster index
		* @n: Maximum number of clusters
		* @offset: Set to first cluster offset
		*
		* This function scans tables for contiguous allocated or free clusters.
		*/
		static unsigned int qed_count_contiguous_clusters(BDRVQEDState *s,
		QEDTable *table,
		unsigned int index,
		unsigned int n,
		uint64_t *offset)
		{
		unsigned int end = MIN(index + n, s->table_nelems);
		uint64_t last = table->offsets[index];
		unsigned int i;

		*offset = last;

		for (i = index + 1; i < end; i++) {
		if (last == 0) {
		/* Counting free clusters */
		if (table->offsets[i] != 0) {
		break;
		}
		} else {
		/* Counting allocated clusters */
		if (table->offsets[i] != last + s->header.cluster_size) {
		break;
		}
		last = table->offsets[i];
		}
		}
		return i - index;
		}

		typedef struct {
		BDRVQEDState *s;
		uint64_t pos;
		size_t len;

		QEDRequest *request;

		/* User callback */
		QEDFindClusterFunc *cb;
		void *opaque;
		} QEDFindClusterCB;

		static void qed_find_cluster_cb(void *opaque, int ret)
		{
		QEDFindClusterCB *find_cluster_cb = opaque;
		BDRVQEDState *s = find_cluster_cb->s;
		QEDRequest *request = find_cluster_cb->request;
		uint64_t offset = 0;
		size_t len = 0;
		unsigned int index;
		unsigned int n;

		if (ret) {
		goto out;
		}

		index = qed_l2_index(s, find_cluster_cb->pos);
		n = qed_bytes_to_clusters(s,
		qed_offset_into_cluster(s, find_cluster_cb->pos) +
		find_cluster_cb->len);
		n = qed_count_contiguous_clusters(s, request->l2_table->table,
		index, n, &offset);

		ret = offset ? QED_CLUSTER_FOUND : QED_CLUSTER_L2;
		len = MIN(find_cluster_cb->len, n * s->header.cluster_size -
		qed_offset_into_cluster(s, find_cluster_cb->pos));

		if (offset && !qed_check_cluster_offset(s, offset)) {
		ret = -EINVAL;
		}

		out:
		find_cluster_cb->cb(find_cluster_cb->opaque, ret, offset, len);
		qemu_free(find_cluster_cb);
		}

		/**
		* Find the offset of a data cluster
		*
		* @s: QED state
		* @request: L2 cache entry
		* @pos: Byte position in device
		* @len: Number of bytes
		* @cb: Completion function
		* @opaque: User data for completion function
		*
		* This function translates a position in the block device to an offset in the
		* image file. It invokes the cb completion callback to report back the
		* translated offset or unallocated range in the image file.
		*
		* If the L2 table exists, request->l2_table points to the L2 table cache entry
		* and the caller must free the reference when they are finished. The cache
		* entry is exposed in this way to avoid callers having to read the L2 table
		* again later during request processing. If request->l2_table is non-NULL it
		* will be unreferenced before taking on the new cache entry.
		*/
		void qed_find_cluster(BDRVQEDState s, QEDRequest request, uint64_t pos,
		size_t len, QEDFindClusterFunc cb, void opaque)
		{
		QEDFindClusterCB *find_cluster_cb;
		uint64_t l2_offset;

		/* Limit length to L2 boundary. Requests are broken up at the L2 boundary
		* so that a request acts on one L2 table at a time.
		*/
		len = MIN(len, (((pos >> s->l1_shift) + 1) << s->l1_shift) - pos);

		l2_offset = s->l1_table->offsets[qed_l1_index(s, pos)];
		if (!l2_offset) {
		cb(opaque, QED_CLUSTER_L1, 0, len);
		return;
		}
		if (!qed_check_table_offset(s, l2_offset)) {
		cb(opaque, -EINVAL, 0, 0);
		return;
		}

		find_cluster_cb = qemu_malloc(sizeof(*find_cluster_cb));
		find_cluster_cb->s = s;
		find_cluster_cb->pos = pos;
		find_cluster_cb->len = len;
		find_cluster_cb->cb = cb;
		find_cluster_cb->opaque = opaque;
		find_cluster_cb->request = request;

		qed_read_l2_table(s, request, l2_offset,
		qed_find_cluster_cb, find_cluster_cb);
		}

block/qed-gencb.c

0 → 100644

+32 −0

Original line number	Diff line number	Diff line
		/*
		* QEMU Enhanced Disk Format
		*
		* Copyright IBM, Corp. 2010
		*
		* Authors:
		* Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
		*
		* This work is licensed under the terms of the GNU LGPL, version 2 or later.
		* See the COPYING.LIB file in the top-level directory.
		*
		*/

		#include "qed.h"

		void gencb_alloc(size_t len, BlockDriverCompletionFunc cb, void *opaque)
		{
		GenericCB *gencb = qemu_malloc(len);
		gencb->cb = cb;
		gencb->opaque = opaque;
		return gencb;
		}

		void gencb_complete(void *opaque, int ret)
		{
		GenericCB *gencb = opaque;
		BlockDriverCompletionFunc *cb = gencb->cb;
		void *user_opaque = gencb->opaque;

		qemu_free(gencb);
		cb(user_opaque, ret);
		}

block/qed-l2-cache.c

0 → 100644

+173 −0

Original line number	Diff line number	Diff line
		/*
		* QEMU Enhanced Disk Format L2 Cache
		*
		* Copyright IBM, Corp. 2010
		*
		* Authors:
		* Anthony Liguori <aliguori@us.ibm.com>
		*
		* This work is licensed under the terms of the GNU LGPL, version 2 or later.
		* See the COPYING.LIB file in the top-level directory.
		*
		*/

		/*
		* L2 table cache usage is as follows:
		*
		* An open image has one L2 table cache that is used to avoid accessing the
		* image file for recently referenced L2 tables.
		*
		* Cluster offset lookup translates the logical offset within the block device
		* to a cluster offset within the image file. This is done by indexing into
		* the L1 and L2 tables which store cluster offsets. It is here where the L2
		* table cache serves up recently referenced L2 tables.
		*
		* If there is a cache miss, that L2 table is read from the image file and
		* committed to the cache. Subsequent accesses to that L2 table will be served
		* from the cache until the table is evicted from the cache.
		*
		* L2 tables are also committed to the cache when new L2 tables are allocated
		* in the image file. Since the L2 table cache is write-through, the new L2
		* table is first written out to the image file and then committed to the
		* cache.
		*
		* Multiple I/O requests may be using an L2 table cache entry at any given
		* time. That means an entry may be in use across several requests and
		* reference counting is needed to free the entry at the correct time. In
		* particular, an entry evicted from the cache will only be freed once all
		* references are dropped.
		*
		* An in-flight I/O request will hold a reference to a L2 table cache entry for
		* the period during which it needs to access the L2 table. This includes
		* cluster offset lookup, L2 table allocation, and L2 table update when a new
		* data cluster has been allocated.
		*
		* An interesting case occurs when two requests need to access an L2 table that
		* is not in the cache. Since the operation to read the table from the image
		* file takes some time to complete, both requests may see a cache miss and
		* start reading the L2 table from the image file. The first to finish will
		* commit its L2 table into the cache. When the second tries to commit its
		* table will be deleted in favor of the existing cache entry.
		*/

		#include "trace.h"
		#include "qed.h"

		/* Each L2 holds 2GB so this let's us fully cache a 100GB disk */
		#define MAX_L2_CACHE_SIZE 50

		/**
		* Initialize the L2 cache
		*/
		void qed_init_l2_cache(L2TableCache *l2_cache)
		{
		QTAILQ_INIT(&l2_cache->entries);
		l2_cache->n_entries = 0;
		}

		/**
		* Free the L2 cache
		*/
		void qed_free_l2_cache(L2TableCache *l2_cache)
		{
		CachedL2Table entry, next_entry;

		QTAILQ_FOREACH_SAFE(entry, &l2_cache->entries, node, next_entry) {
		qemu_vfree(entry->table);
		qemu_free(entry);
		}
		}

		/**
		* Allocate an uninitialized entry from the cache
		*
		* The returned entry has a reference count of 1 and is owned by the caller.
		* The caller must allocate the actual table field for this entry and it must
		* be freeable using qemu_vfree().
		*/
		CachedL2Table qed_alloc_l2_cache_entry(L2TableCache l2_cache)
		{
		CachedL2Table *entry;

		entry = qemu_mallocz(sizeof(*entry));
		entry->ref++;

		trace_qed_alloc_l2_cache_entry(l2_cache, entry);

		return entry;
		}

		/**
		* Decrease an entry's reference count and free if necessary when the reference
		* count drops to zero.
		*/
		void qed_unref_l2_cache_entry(CachedL2Table *entry)
		{
		if (!entry) {
		return;
		}

		entry->ref--;
		trace_qed_unref_l2_cache_entry(entry, entry->ref);
		if (entry->ref == 0) {
		qemu_vfree(entry->table);
		qemu_free(entry);
		}
		}

		/**
		* Find an entry in the L2 cache. This may return NULL and it's up to the
		* caller to satisfy the cache miss.
		*
		* For a cached entry, this function increases the reference count and returns
		* the entry.
		*/
		CachedL2Table qed_find_l2_cache_entry(L2TableCache l2_cache, uint64_t offset)
		{
		CachedL2Table *entry;

		QTAILQ_FOREACH(entry, &l2_cache->entries, node) {
		if (entry->offset == offset) {
		trace_qed_find_l2_cache_entry(l2_cache, entry, offset, entry->ref);
		entry->ref++;
		return entry;
		}
		}
		return NULL;
		}

		/**
		* Commit an L2 cache entry into the cache. This is meant to be used as part of
		* the process to satisfy a cache miss. A caller would allocate an entry which
		* is not actually in the L2 cache and then once the entry was valid and
		* present on disk, the entry can be committed into the cache.
		*
		* Since the cache is write-through, it's important that this function is not
		* called until the entry is present on disk and the L1 has been updated to
		* point to the entry.
		*
		* N.B. This function steals a reference to the l2_table from the caller so the
		* caller must obtain a new reference by issuing a call to
		* qed_find_l2_cache_entry().
		*/
		void qed_commit_l2_cache_entry(L2TableCache l2_cache, CachedL2Table l2_table)
		{
		CachedL2Table *entry;

		entry = qed_find_l2_cache_entry(l2_cache, l2_table->offset);
		if (entry) {
		qed_unref_l2_cache_entry(entry);
		qed_unref_l2_cache_entry(l2_table);
		return;
		}

		if (l2_cache->n_entries >= MAX_L2_CACHE_SIZE) {
		entry = QTAILQ_FIRST(&l2_cache->entries);
		QTAILQ_REMOVE(&l2_cache->entries, entry, node);
		l2_cache->n_entries--;
		qed_unref_l2_cache_entry(entry);
		}

		l2_cache->n_entries++;
		QTAILQ_INSERT_TAIL(&l2_cache->entries, l2_table, node);
		}

block/qed-table.c

0 → 100644

+319 −0

Original line number	Diff line number	Diff line
		/*
		* QEMU Enhanced Disk Format Table I/O
		*
		* Copyright IBM, Corp. 2010
		*
		* Authors:
		* Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
		* Anthony Liguori <aliguori@us.ibm.com>
		*
		* This work is licensed under the terms of the GNU LGPL, version 2 or later.
		* See the COPYING.LIB file in the top-level directory.
		*
		*/

		#include "trace.h"
		#include "qemu_socket.h" /* for EINPROGRESS on Windows */
		#include "qed.h"

		typedef struct {
		GenericCB gencb;
		BDRVQEDState *s;
		QEDTable *table;

		struct iovec iov;
		QEMUIOVector qiov;
		} QEDReadTableCB;

		static void qed_read_table_cb(void *opaque, int ret)
		{
		QEDReadTableCB *read_table_cb = opaque;
		QEDTable *table = read_table_cb->table;
		int noffsets = read_table_cb->iov.iov_len / sizeof(uint64_t);
		int i;

		/* Handle I/O error */
		if (ret) {
		goto out;
		}

		/* Byteswap offsets */
		for (i = 0; i < noffsets; i++) {
		table->offsets[i] = le64_to_cpu(table->offsets[i]);
		}

		out:
		/* Completion */
		trace_qed_read_table_cb(read_table_cb->s, read_table_cb->table, ret);
		gencb_complete(&read_table_cb->gencb, ret);
		}

		static void qed_read_table(BDRVQEDState s, uint64_t offset, QEDTable table,
		BlockDriverCompletionFunc cb, void opaque)
		{
		QEDReadTableCB read_table_cb = gencb_alloc(sizeof(read_table_cb),
		cb, opaque);
		QEMUIOVector *qiov = &read_table_cb->qiov;
		BlockDriverAIOCB *aiocb;

		trace_qed_read_table(s, offset, table);

		read_table_cb->s = s;
		read_table_cb->table = table;
		read_table_cb->iov.iov_base = table->offsets,
		read_table_cb->iov.iov_len = s->header.cluster_size * s->header.table_size,

		qemu_iovec_init_external(qiov, &read_table_cb->iov, 1);
		aiocb = bdrv_aio_readv(s->bs->file, offset / BDRV_SECTOR_SIZE, qiov,
		read_table_cb->iov.iov_len / BDRV_SECTOR_SIZE,
		qed_read_table_cb, read_table_cb);
		if (!aiocb) {
		qed_read_table_cb(read_table_cb, -EIO);
		}
		}

		typedef struct {
		GenericCB gencb;
		BDRVQEDState *s;
		QEDTable *orig_table;
		QEDTable *table;
		bool flush; /* flush after write? */

		struct iovec iov;
		QEMUIOVector qiov;
		} QEDWriteTableCB;

		static void qed_write_table_cb(void *opaque, int ret)
		{
		QEDWriteTableCB *write_table_cb = opaque;

		trace_qed_write_table_cb(write_table_cb->s,
		write_table_cb->orig_table,
		write_table_cb->flush,
		ret);

		if (ret) {
		goto out;
		}

		if (write_table_cb->flush) {
		/* We still need to flush first */
		write_table_cb->flush = false;
		bdrv_aio_flush(write_table_cb->s->bs, qed_write_table_cb,
		write_table_cb);
		return;
		}

		out:
		qemu_vfree(write_table_cb->table);
		gencb_complete(&write_table_cb->gencb, ret);
		return;
		}

		/**
		* Write out an updated part or all of a table
		*
		* @s: QED state
		* @offset: Offset of table in image file, in bytes
		* @table: Table
		* @index: Index of first element
		* @n: Number of elements
		* @flush: Whether or not to sync to disk
		* @cb: Completion function
		* @opaque: Argument for completion function
		*/
		static void qed_write_table(BDRVQEDState s, uint64_t offset, QEDTable table,
		unsigned int index, unsigned int n, bool flush,
		BlockDriverCompletionFunc cb, void opaque)
		{
		QEDWriteTableCB *write_table_cb;
		BlockDriverAIOCB *aiocb;
		unsigned int sector_mask = BDRV_SECTOR_SIZE / sizeof(uint64_t) - 1;
		unsigned int start, end, i;
		size_t len_bytes;

		trace_qed_write_table(s, offset, table, index, n);

		/* Calculate indices of the first and one after last elements */
		start = index & ~sector_mask;
		end = (index + n + sector_mask) & ~sector_mask;

		len_bytes = (end - start) * sizeof(uint64_t);

		write_table_cb = gencb_alloc(sizeof(*write_table_cb), cb, opaque);
		write_table_cb->s = s;
		write_table_cb->orig_table = table;
		write_table_cb->flush = flush;
		write_table_cb->table = qemu_blockalign(s->bs, len_bytes);
		write_table_cb->iov.iov_base = write_table_cb->table->offsets;
		write_table_cb->iov.iov_len = len_bytes;
		qemu_iovec_init_external(&write_table_cb->qiov, &write_table_cb->iov, 1);

		/* Byteswap table */
		for (i = start; i < end; i++) {
		uint64_t le_offset = cpu_to_le64(table->offsets[i]);
		write_table_cb->table->offsets[i - start] = le_offset;
		}

		/* Adjust for offset into table */
		offset += start * sizeof(uint64_t);

		aiocb = bdrv_aio_writev(s->bs->file, offset / BDRV_SECTOR_SIZE,
		&write_table_cb->qiov,
		write_table_cb->iov.iov_len / BDRV_SECTOR_SIZE,
		qed_write_table_cb, write_table_cb);
		if (!aiocb) {
		qed_write_table_cb(write_table_cb, -EIO);
		}
		}

		/**
		* Propagate return value from async callback
		*/
		static void qed_sync_cb(void *opaque, int ret)
		{
		(int )opaque = ret;
		}

		int qed_read_l1_table_sync(BDRVQEDState *s)
		{
		int ret = -EINPROGRESS;

		async_context_push();

		qed_read_table(s, s->header.l1_table_offset,
		s->l1_table, qed_sync_cb, &ret);
		while (ret == -EINPROGRESS) {
		qemu_aio_wait();
		}

		async_context_pop();

		return ret;
		}

		void qed_write_l1_table(BDRVQEDState *s, unsigned int index, unsigned int n,
		BlockDriverCompletionFunc cb, void opaque)
		{
		BLKDBG_EVENT(s->bs->file, BLKDBG_L1_UPDATE);
		qed_write_table(s, s->header.l1_table_offset,
		s->l1_table, index, n, false, cb, opaque);
		}

		int qed_write_l1_table_sync(BDRVQEDState *s, unsigned int index,
		unsigned int n)
		{
		int ret = -EINPROGRESS;

		async_context_push();

		qed_write_l1_table(s, index, n, qed_sync_cb, &ret);
		while (ret == -EINPROGRESS) {
		qemu_aio_wait();
		}

		async_context_pop();

		return ret;
		}

		typedef struct {
		GenericCB gencb;
		BDRVQEDState *s;
		uint64_t l2_offset;
		QEDRequest *request;
		} QEDReadL2TableCB;

		static void qed_read_l2_table_cb(void *opaque, int ret)
		{
		QEDReadL2TableCB *read_l2_table_cb = opaque;
		QEDRequest *request = read_l2_table_cb->request;
		BDRVQEDState *s = read_l2_table_cb->s;
		CachedL2Table *l2_table = request->l2_table;

		if (ret) {
		/* can't trust loaded L2 table anymore */
		qed_unref_l2_cache_entry(l2_table);
		request->l2_table = NULL;
		} else {
		l2_table->offset = read_l2_table_cb->l2_offset;

		qed_commit_l2_cache_entry(&s->l2_cache, l2_table);

		/* This is guaranteed to succeed because we just committed the entry
		* to the cache.
		*/
		request->l2_table = qed_find_l2_cache_entry(&s->l2_cache,
		l2_table->offset);
		assert(request->l2_table != NULL);
		}

		gencb_complete(&read_l2_table_cb->gencb, ret);
		}

		void qed_read_l2_table(BDRVQEDState s, QEDRequest request, uint64_t offset,
		BlockDriverCompletionFunc cb, void opaque)
		{
		QEDReadL2TableCB *read_l2_table_cb;

		qed_unref_l2_cache_entry(request->l2_table);

		/* Check for cached L2 entry */
		request->l2_table = qed_find_l2_cache_entry(&s->l2_cache, offset);
		if (request->l2_table) {
		cb(opaque, 0);
		return;
		}

		request->l2_table = qed_alloc_l2_cache_entry(&s->l2_cache);
		request->l2_table->table = qed_alloc_table(s);

		read_l2_table_cb = gencb_alloc(sizeof(*read_l2_table_cb), cb, opaque);
		read_l2_table_cb->s = s;
		read_l2_table_cb->l2_offset = offset;
		read_l2_table_cb->request = request;

		BLKDBG_EVENT(s->bs->file, BLKDBG_L2_LOAD);
		qed_read_table(s, offset, request->l2_table->table,
		qed_read_l2_table_cb, read_l2_table_cb);
		}

		int qed_read_l2_table_sync(BDRVQEDState s, QEDRequest request, uint64_t offset)
		{
		int ret = -EINPROGRESS;

		async_context_push();

		qed_read_l2_table(s, request, offset, qed_sync_cb, &ret);
		while (ret == -EINPROGRESS) {
		qemu_aio_wait();
		}

		async_context_pop();
		return ret;
		}

		void qed_write_l2_table(BDRVQEDState s, QEDRequest request,
		unsigned int index, unsigned int n, bool flush,
		BlockDriverCompletionFunc cb, void opaque)
		{
		BLKDBG_EVENT(s->bs->file, BLKDBG_L2_UPDATE);
		qed_write_table(s, request->l2_table->offset,
		request->l2_table->table, index, n, flush, cb, opaque);
		}

		int qed_write_l2_table_sync(BDRVQEDState s, QEDRequest request,
		unsigned int index, unsigned int n, bool flush)
		{
		int ret = -EINPROGRESS;

		async_context_push();

		qed_write_l2_table(s, request, index, n, flush, qed_sync_cb, &ret);
		while (ret == -EINPROGRESS) {
		qemu_aio_wait();
		}

		async_context_pop();
		return ret;
		}