xref: /kvmtool/disk/qcow.c (revision fe8bdde0bd72210f0cfeb36bcdd802708d66c4ea)

#include "kvm/qcow.h"

#include "kvm/disk-image.h"
#include "kvm/read-write.h"
#include "kvm/util.h"

#include <sys/types.h>
#include <sys/stat.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>

#include <linux/byteorder.h>
#include <linux/kernel.h>
#include <linux/types.h>

static int insert(struct rb_root *root, struct qcow_l2_table *new)
{
	struct rb_node **link = &(root->rb_node), *parent = NULL;
	u64 offset = new->offset;

	/* search the tree */
	while (*link) {
		struct qcow_l2_table *t;

		t = rb_entry(*link, struct qcow_l2_table, node);
		if (!t)
			goto error;

		parent = *link;

		if (t->offset > offset)
			link = &(*link)->rb_left;
		else if (t->offset < offset)
			link = &(*link)->rb_right;
		else
			goto out;
	}

	/* add new node */
	rb_link_node(&new->node, parent, link);
	rb_insert_color(&new->node, root);
out:
	return 0;
error:
	return -1;
}

static struct qcow_l2_table *search(struct rb_root *root, u64 offset)
{
	struct rb_node *link = root->rb_node;

	while (link) {
		struct qcow_l2_table *t;

		t = rb_entry(link, struct qcow_l2_table, node);
		if (!t)
			goto out;

		if (t->offset > offset)
			link = link->rb_left;
		else if (t->offset < offset)
			link = link->rb_right;
		else
			return t;
	}
out:
	return NULL;
}

static void free_cache(struct qcow *q)
{
	struct list_head *pos, *n;
	struct qcow_l2_table *t;
	struct rb_root *r = &q->root;

	list_for_each_safe(pos, n, &q->lru_list) {
		/* Remove cache table from the list and RB tree */
		list_del(pos);
		t = list_entry(pos, struct qcow_l2_table, list);
		rb_erase(&t->node, r);

		/* Free the cached node */
		free(t);
	}
}

static int cache_table(struct qcow *q, struct qcow_l2_table *c)
{
	struct rb_root *r = &q->root;
	struct qcow_l2_table *lru;

	if (q->nr_cached == MAX_CACHE_NODES) {
		/*
		 * The node at the head of the list is least recently used
		 * node. Remove it from the list and replaced with a new node.
		 */
		lru = list_first_entry(&q->lru_list, struct qcow_l2_table, list);

		/* Remove the node from the cache */
		rb_erase(&lru->node, r);
		list_del_init(&lru->list);
		q->nr_cached--;

		/* Free the LRUed node */
		free(lru);
	}

	/* Add new node in RB Tree: Helps in searching faster */
	if (insert(r, c) < 0)
		goto error;

	/* Add in LRU replacement list */
	list_add_tail(&c->list, &q->lru_list);
	q->nr_cached++;

	return 0;
error:
	return -1;
}

static struct qcow_l2_table *search_table(struct qcow *q, u64 offset)
{
	struct qcow_l2_table *l2t;

	l2t = search(&q->root, offset);
	if (!l2t)
		return NULL;

	/* Update the LRU state, by moving the searched node to list tail */
	list_move_tail(&l2t->list, &q->lru_list);

	return l2t;
}

/* Allocates a new node for caching L2 table */
static struct qcow_l2_table *new_cache_table(struct qcow *q, u64 offset)
{
	struct qcow_header *header = q->header;
	struct qcow_l2_table *c;
	u64 l2t_sz;
	u64 size;

	l2t_sz = 1 << header->l2_bits;
	size   = sizeof(*c) + l2t_sz * sizeof(u64);
	c      = calloc(1, size);
	if (!c)
		goto out;

	c->offset = offset;
	RB_CLEAR_NODE(&c->node);
	INIT_LIST_HEAD(&c->list);
out:
	return c;
}

static inline u64 get_l1_index(struct qcow *q, u64 offset)
{
	struct qcow_header *header = q->header;

	return offset >> (header->l2_bits + header->cluster_bits);
}

static inline u64 get_l2_index(struct qcow *q, u64 offset)
{
	struct qcow_header *header = q->header;

	return (offset >> (header->cluster_bits)) & ((1 << header->l2_bits)-1);
}

static inline u64 get_cluster_offset(struct qcow *q, u64 offset)
{
	struct qcow_header *header = q->header;

	return offset & ((1 << header->cluster_bits)-1);
}

static struct qcow_l2_table *qcow_read_l2_table(struct qcow *q, u64 offset)
{
	struct qcow_header *header = q->header;
	struct qcow_l2_table *l2t;
	u64 size;
	u64 i;

	size = 1 << header->l2_bits;

	/* search an entry for offset in cache */
	l2t = search_table(q, offset);
	if (l2t)
		return l2t;

	/* allocate new node for caching l2 table */
	l2t = new_cache_table(q, offset);
	if (!l2t)
		goto error;

	/* table not cached: read from the disk */
	if (pread_in_full(q->fd, l2t->table, size * sizeof(u64), offset) < 0)
		goto error;

	/* cache the table */
	if (cache_table(q, l2t) < 0)
		goto error;

	/* change cached table to CPU's byte-order */
	for (i = 0; i < size; i++)
		be64_to_cpus(&l2t->table[i]);

	return l2t;
error:
	free(l2t);
	return NULL;
}

static ssize_t qcow_read_cluster(struct qcow *q, u64 offset, void *dst, u32 dst_len)
{
	struct qcow_header *header = q->header;
	struct qcow_table *table  = &q->table;
	struct qcow_l2_table *l2_table;
	u64 l2_table_offset;
	u64 l2_table_size;
	u64 cluster_size;
	u64 clust_offset;
	u64 clust_start;
	size_t length;
	u64 l1_idx;
	u64 l2_idx;

	cluster_size = 1 << header->cluster_bits;

	l1_idx = get_l1_index(q, offset);
	if (l1_idx >= table->table_size)
		goto out_error;

	clust_offset = get_cluster_offset(q, offset);
	if (clust_offset >= cluster_size)
		goto out_error;

	length = cluster_size - clust_offset;
	if (length > dst_len)
		length = dst_len;

	l2_table_offset = table->l1_table[l1_idx] & ~header->oflag_mask;
	if (!l2_table_offset)
		goto zero_cluster;

	l2_table_size = 1 << header->l2_bits;

	/* read and cache level 2 table */
	l2_table = qcow_read_l2_table(q, l2_table_offset);
	if (!l2_table)
		goto out_error;

	l2_idx = get_l2_index(q, offset);
	if (l2_idx >= l2_table_size)
		goto out_error;

	clust_start = l2_table->table[l2_idx] & ~header->oflag_mask;
	if (!clust_start)
		goto zero_cluster;

	if (pread_in_full(q->fd, dst, length, clust_start + clust_offset) < 0)
		goto out_error;

out:
	return length;

zero_cluster:
	memset(dst, 0, length);
	goto out;

out_error:
	length = -1;
	goto out;
}

static ssize_t qcow_read_sector(struct disk_image *disk, u64 sector, void *dst, u32 dst_len)
{
	struct qcow *q = disk->priv;
	struct qcow_header *header = q->header;
	u32 nr_read;
	u64 offset;
	char *buf;
	u32 nr;

	buf		= dst;
	nr_read		= 0;

	while (nr_read < dst_len) {
		offset		= sector << SECTOR_SHIFT;
		if (offset >= header->size)
			return -1;

		nr = qcow_read_cluster(q, offset, buf, dst_len - nr_read);
		if (nr <= 0)
			return -1;

		nr_read		+= nr;
		buf		+= nr;
		sector		+= (nr >> SECTOR_SHIFT);
	}

	return dst_len;
}

static inline u64 file_size(int fd)
{
	struct stat st;

	if (fstat(fd, &st) < 0)
		return 0;

	return st.st_size;
}

static inline int qcow_pwrite_sync(int fd, void *buf, size_t count, off_t offset)
{
	if (pwrite_in_full(fd, buf, count, offset) < 0)
		return -1;

	return fdatasync(fd);
}

/* Writes a level 2 table at the end of the file. */
static u64 qcow_write_l2_table(struct qcow *q, u64 *table)
{
	struct qcow_header *header = q->header;
	u64 clust_sz;
	u64 f_sz;
	u64 off;
	u64 sz;

	f_sz		= file_size(q->fd);
	if (!f_sz)
		return 0;

	sz		= 1 << header->l2_bits;
	clust_sz	= 1 << header->cluster_bits;
	off		= ALIGN(f_sz, clust_sz);

	if (qcow_pwrite_sync(q->fd, table, sz * sizeof(u64), off) < 0)
		return 0;

	return off;
}

/*
 * QCOW file might grow during a write operation. Not only data but metadata is
 * also written at the end of the file. Therefore it is necessary to ensure
 * every write is committed to disk. Hence we use uses qcow_pwrite_sync() to
 * synchronize the in-core state of QCOW image to disk.
 *
 * We also try to restore the image to a consistent state if the metdata
 * operation fails. The two metadat operations are: level 1 and level 2 table
 * update. If either of them fails the image is truncated to a consistent state.
 */
static ssize_t qcow_write_cluster(struct qcow *q, u64 offset, void *buf, u32 src_len)
{
	struct qcow_header *header = q->header;
	struct qcow_table  *table  = &q->table;
	struct qcow_l2_table *l2t;
	bool update_meta;
	u64 clust_start;
	u64 clust_off;
	u64 clust_sz;
	u64 l1t_idx;
	u64 l2t_idx;
	u64 l2t_off;
	u64 l2t_sz;
	u64 f_sz;
	u64 len;
	u64 t;

	l2t		= NULL;
	l2t_sz		= 1 << header->l2_bits;
	clust_sz	= 1 << header->cluster_bits;

	l1t_idx		= get_l1_index(q, offset);
	if (l1t_idx >= table->table_size)
		goto error;

	l2t_idx		= get_l2_index(q, offset);
	if (l2t_idx >= l2t_sz)
		goto error;

	clust_off	= get_cluster_offset(q, offset);
	if (clust_off >= clust_sz)
		goto error;

	len		= clust_sz - clust_off;
	if (len > src_len)
		len = src_len;

	l2t_off		= table->l1_table[l1t_idx] & ~header->oflag_mask;
	if (l2t_off) {
		/* read and cache l2 table */
		l2t = qcow_read_l2_table(q, l2t_off);
		if (!l2t)
			goto error;
	} else {
		l2t = new_cache_table(q, l2t_off);
		if (!l2t)
			goto error;

		/* Capture the state of the consistent QCOW image */
		f_sz		= file_size(q->fd);
		if (!f_sz)
			goto free_cache;

		/* Write the l2 table of 0's at the end of the file */
		l2t_off		= qcow_write_l2_table(q, l2t->table);
		if (!l2t_off)
			goto free_cache;

		/* Metadata update: update on disk level 1 table */
		t		= cpu_to_be64(l2t_off);

		if (qcow_pwrite_sync(q->fd, &t, sizeof(t), header->l1_table_offset + l1t_idx * sizeof(u64)) < 0) {
			/* restore file to consistent state */
			if (ftruncate(q->fd, f_sz) < 0)
				goto free_cache;

			goto free_cache;
		}

		if (cache_table(q, l2t) < 0) {
			if (ftruncate(q->fd, f_sz) < 0)
				goto free_cache;

			goto free_cache;
		}

		/* Update the in-core entry */
		table->l1_table[l1t_idx] = l2t_off;
	}

	/* Capture the state of the consistent QCOW image */
	f_sz		= file_size(q->fd);
	if (!f_sz)
		goto error;

	clust_start	= l2t->table[l2t_idx] & ~header->oflag_mask;
	if (!clust_start) {
		clust_start	= ALIGN(f_sz, clust_sz);
		update_meta	= true;
	} else
		update_meta	= false;

	/* Write actual data */
	if (pwrite_in_full(q->fd, buf, len, clust_start + clust_off) < 0)
		goto error;

	if (update_meta) {
		t = cpu_to_be64(clust_start);
		if (qcow_pwrite_sync(q->fd, &t, sizeof(t), l2t_off + l2t_idx * sizeof(u64)) < 0) {
			/* Restore the file to consistent state */
			if (ftruncate(q->fd, f_sz) < 0)
				goto error;

			goto error;
		}

		/* Update the cached level2 entry */
		l2t->table[l2t_idx] = clust_start;
	}

	return len;

free_cache:
	free(l2t);
error:
	return -1;
}

static ssize_t qcow_write_sector(struct disk_image *disk, u64 sector, void *src, u32 src_len)
{
	struct qcow *q = disk->priv;
	struct qcow_header *header = q->header;
	u32 nr_written;
	char *buf;
	u64 offset;
	ssize_t nr;

	buf		= src;
	nr_written	= 0;
	offset		= sector << SECTOR_SHIFT;

	while (nr_written < src_len) {
		if (offset >= header->size)
			return -1;

		nr = qcow_write_cluster(q, offset, buf, src_len - nr_written);
		if (nr < 0)
			return -1;

		nr_written	+= nr;
		buf		+= nr;
		offset		+= nr;
	}

	return nr_written;
}

static ssize_t qcow_nowrite_sector(struct disk_image *disk, u64 sector, void *src, u32 src_len)
{
	/* I/O error */
	pr_info("%s: no write support\n", __func__);
	return -1;
}

static int qcow_disk_close(struct disk_image *disk)
{
	struct qcow *q;

	if (!disk)
		return 0;

	q = disk->priv;

	free_cache(q);
	free(q->table.l1_table);
	free(q->header);
	free(q);

	return 0;
}

static struct disk_image_operations qcow_disk_readonly_ops = {
	.read_sector		= qcow_read_sector,
	.write_sector		= qcow_nowrite_sector,
	.close			= qcow_disk_close,
};

static struct disk_image_operations qcow_disk_ops = {
	.read_sector		= qcow_read_sector,
	.write_sector		= qcow_write_sector,
	.close			= qcow_disk_close,
};

static int qcow_read_l1_table(struct qcow *q)
{
	struct qcow_header *header = q->header;
	struct qcow_table *table = &q->table;
	u64 i;

	table->table_size	= header->l1_size;

	table->l1_table	= calloc(table->table_size, sizeof(u64));
	if (!table->l1_table)
		return -1;

	if (pread_in_full(q->fd, table->l1_table, sizeof(u64) *
				table->table_size, header->l1_table_offset) < 0)
		return -1;

	for (i = 0; i < table->table_size; i++)
		be64_to_cpus(&table->l1_table[i]);

	return 0;
}

static void *qcow2_read_header(int fd)
{
	struct qcow2_header_disk f_header;
	struct qcow_header *header;

	header = malloc(sizeof(struct qcow_header));
	if (!header)
		return NULL;

	if (pread_in_full(fd, &f_header, sizeof(struct qcow2_header_disk), 0) < 0) {
		free(header);
		return NULL;
	}

	be32_to_cpus(&f_header.magic);
	be32_to_cpus(&f_header.version);
	be64_to_cpus(&f_header.backing_file_offset);
	be32_to_cpus(&f_header.backing_file_size);
	be32_to_cpus(&f_header.cluster_bits);
	be64_to_cpus(&f_header.size);
	be32_to_cpus(&f_header.crypt_method);
	be32_to_cpus(&f_header.l1_size);
	be64_to_cpus(&f_header.l1_table_offset);
	be64_to_cpus(&f_header.refcount_table_offset);
	be32_to_cpus(&f_header.refcount_table_clusters);
	be32_to_cpus(&f_header.nb_snapshots);
	be64_to_cpus(&f_header.snapshots_offset);

	*header		= (struct qcow_header) {
		.size			= f_header.size,
		.l1_table_offset	= f_header.l1_table_offset,
		.l1_size		= f_header.l1_size,
		.cluster_bits		= f_header.cluster_bits,
		.l2_bits		= f_header.cluster_bits - 3,
		.oflag_mask		= QCOW2_OFLAG_MASK,
	};

	return header;
}

static struct disk_image *qcow2_probe(int fd, bool readonly)
{
	struct qcow *q;
	struct qcow_header *h;
	struct disk_image *disk_image;

	q = calloc(1, sizeof(struct qcow));
	if (!q)
		goto error;

	q->fd = fd;
	q->root = RB_ROOT;
	INIT_LIST_HEAD(&q->lru_list);

	h = q->header = qcow2_read_header(fd);
	if (!h)
		goto error;

	if (qcow_read_l1_table(q) < 0)
		goto error;

	/*
	 * Do not use mmap use read/write instead
	 */
	if (readonly)
		disk_image = disk_image__new(fd, h->size, &qcow_disk_readonly_ops, DISK_IMAGE_NOMMAP);
	else
		disk_image = disk_image__new(fd, h->size, &qcow_disk_ops, DISK_IMAGE_NOMMAP);

	if (!disk_image)
		goto error;
	disk_image->priv = q;

	return disk_image;
error:
	if (!q)
		return NULL;

	free(q->table.l1_table);
	free(q->header);
	free(q);

	return NULL;
}

static bool qcow2_check_image(int fd)
{
	struct qcow2_header_disk f_header;

	if (pread_in_full(fd, &f_header, sizeof(struct qcow2_header_disk), 0) < 0)
		return false;

	be32_to_cpus(&f_header.magic);
	be32_to_cpus(&f_header.version);

	if (f_header.magic != QCOW_MAGIC)
		return false;

	if (f_header.version != QCOW2_VERSION)
		return false;

	return true;
}

static void *qcow1_read_header(int fd)
{
	struct qcow1_header_disk f_header;
	struct qcow_header *header;

	header = malloc(sizeof(struct qcow_header));
	if (!header)
		return NULL;

	if (pread_in_full(fd, &f_header, sizeof(struct qcow1_header_disk), 0) < 0) {
		free(header);
		return NULL;
	}

	be32_to_cpus(&f_header.magic);
	be32_to_cpus(&f_header.version);
	be64_to_cpus(&f_header.backing_file_offset);
	be32_to_cpus(&f_header.backing_file_size);
	be32_to_cpus(&f_header.mtime);
	be64_to_cpus(&f_header.size);
	be32_to_cpus(&f_header.crypt_method);
	be64_to_cpus(&f_header.l1_table_offset);

	*header		= (struct qcow_header) {
		.size			= f_header.size,
		.l1_table_offset	= f_header.l1_table_offset,
		.l1_size		= f_header.size / ((1 << f_header.l2_bits) * (1 << f_header.cluster_bits)),
		.cluster_bits		= f_header.cluster_bits,
		.l2_bits		= f_header.l2_bits,
		.oflag_mask		= QCOW1_OFLAG_MASK,
	};

	return header;
}

static struct disk_image *qcow1_probe(int fd, bool readonly)
{
	struct qcow *q;
	struct qcow_header *h;
	struct disk_image *disk_image;

	q = calloc(1, sizeof(struct qcow));
	if (!q)
		goto error;

	q->fd = fd;
	q->root = RB_ROOT;
	INIT_LIST_HEAD(&q->lru_list);

	h = q->header = qcow1_read_header(fd);
	if (!h)
		goto error;

	if (qcow_read_l1_table(q) < 0)
		goto error;

	/*
	 * Do not use mmap use read/write instead
	 */
	if (readonly)
		disk_image = disk_image__new(fd, h->size, &qcow_disk_readonly_ops, DISK_IMAGE_NOMMAP);
	else
		disk_image = disk_image__new(fd, h->size, &qcow_disk_ops, DISK_IMAGE_NOMMAP);

	if (!disk_image)
		goto error;
	disk_image->priv = q;

	return disk_image;
error:
	if (!q)
		return NULL;

	free(q->table.l1_table);
	free(q->header);
	free(q);

	return NULL;
}

static bool qcow1_check_image(int fd)
{
	struct qcow1_header_disk f_header;

	if (pread_in_full(fd, &f_header, sizeof(struct qcow1_header_disk), 0) < 0)
		return false;

	be32_to_cpus(&f_header.magic);
	be32_to_cpus(&f_header.version);

	if (f_header.magic != QCOW_MAGIC)
		return false;

	if (f_header.version != QCOW1_VERSION)
		return false;

	return true;
}

struct disk_image *qcow_probe(int fd, bool readonly)
{
	if (qcow1_check_image(fd))
		return qcow1_probe(fd, readonly);

	if (qcow2_check_image(fd))
		return qcow2_probe(fd, readonly);

	return NULL;
}