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qemu-e2k/block/qcow2-cluster.c
Anton Nefedov c8bb23cbdb qcow2: skip writing zero buffers to empty COW areas 
If COW areas of the newly allocated clusters are zeroes on the backing
image, efficient bdrv_write_zeroes(flags=BDRV_REQ_NO_FALLBACK) can be
used on the whole cluster instead of writing explicit zero buffers later
in perform_cow().

iotest 060:
write to the discarded cluster does not trigger COW anymore.
Use a backing image instead.

Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>
Message-id: 20190516142749.81019-2-anton.nefedov@virtuozzo.com
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
2019-05-28 20:30:55 +02:00

2122 lines
70 KiB
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/*
* Block driver for the QCOW version 2 format
*
* Copyright (c) 2004-2006 Fabrice Bellard
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#include "qemu/osdep.h"
#include <zlib.h>
#include "qapi/error.h"
#include "qemu-common.h"
#include "qcow2.h"
#include "qemu/bswap.h"
#include "trace.h"
int qcow2_shrink_l1_table(BlockDriverState *bs, uint64_t exact_size)
{
BDRVQcow2State *s = bs->opaque;
int new_l1_size, i, ret;
if (exact_size >= s->l1_size) {
return 0;
}
new_l1_size = exact_size;
#ifdef DEBUG_ALLOC2
fprintf(stderr, "shrink l1_table from %d to %d\n", s->l1_size, new_l1_size);
#endif
BLKDBG_EVENT(bs->file, BLKDBG_L1_SHRINK_WRITE_TABLE);
ret = bdrv_pwrite_zeroes(bs->file, s->l1_table_offset +
new_l1_size * sizeof(uint64_t),
(s->l1_size - new_l1_size) * sizeof(uint64_t), 0);
if (ret < 0) {
goto fail;
}
ret = bdrv_flush(bs->file->bs);
if (ret < 0) {
goto fail;
}
BLKDBG_EVENT(bs->file, BLKDBG_L1_SHRINK_FREE_L2_CLUSTERS);
for (i = s->l1_size - 1; i > new_l1_size - 1; i--) {
if ((s->l1_table[i] & L1E_OFFSET_MASK) == 0) {
continue;
}
qcow2_free_clusters(bs, s->l1_table[i] & L1E_OFFSET_MASK,
s->cluster_size, QCOW2_DISCARD_ALWAYS);
s->l1_table[i] = 0;
}
return 0;
fail:
/*
* If the write in the l1_table failed the image may contain a partially
* overwritten l1_table. In this case it would be better to clear the
* l1_table in memory to avoid possible image corruption.
*/
memset(s->l1_table + new_l1_size, 0,
(s->l1_size - new_l1_size) * sizeof(uint64_t));
return ret;
}
int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t min_size,
bool exact_size)
{
BDRVQcow2State *s = bs->opaque;
int new_l1_size2, ret, i;
uint64_t *new_l1_table;
int64_t old_l1_table_offset, old_l1_size;
int64_t new_l1_table_offset, new_l1_size;
uint8_t data[12];
if (min_size <= s->l1_size)
return 0;
/* Do a sanity check on min_size before trying to calculate new_l1_size
* (this prevents overflows during the while loop for the calculation of
* new_l1_size) */
if (min_size > INT_MAX / sizeof(uint64_t)) {
return -EFBIG;
}
if (exact_size) {
new_l1_size = min_size;
} else {
/* Bump size up to reduce the number of times we have to grow */
new_l1_size = s->l1_size;
if (new_l1_size == 0) {
new_l1_size = 1;
}
while (min_size > new_l1_size) {
new_l1_size = DIV_ROUND_UP(new_l1_size * 3, 2);
}
}
QEMU_BUILD_BUG_ON(QCOW_MAX_L1_SIZE > INT_MAX);
if (new_l1_size > QCOW_MAX_L1_SIZE / sizeof(uint64_t)) {
return -EFBIG;
}
#ifdef DEBUG_ALLOC2
fprintf(stderr, "grow l1_table from %d to %" PRId64 "\n",
s->l1_size, new_l1_size);
#endif
new_l1_size2 = sizeof(uint64_t) * new_l1_size;
new_l1_table = qemu_try_blockalign(bs->file->bs,
ROUND_UP(new_l1_size2, 512));
if (new_l1_table == NULL) {
return -ENOMEM;
}
memset(new_l1_table, 0, ROUND_UP(new_l1_size2, 512));
if (s->l1_size) {
memcpy(new_l1_table, s->l1_table, s->l1_size * sizeof(uint64_t));
}
/* write new table (align to cluster) */
BLKDBG_EVENT(bs->file, BLKDBG_L1_GROW_ALLOC_TABLE);
new_l1_table_offset = qcow2_alloc_clusters(bs, new_l1_size2);
if (new_l1_table_offset < 0) {
qemu_vfree(new_l1_table);
return new_l1_table_offset;
}
ret = qcow2_cache_flush(bs, s->refcount_block_cache);
if (ret < 0) {
goto fail;
}
/* the L1 position has not yet been updated, so these clusters must
* indeed be completely free */
ret = qcow2_pre_write_overlap_check(bs, 0, new_l1_table_offset,
new_l1_size2, false);
if (ret < 0) {
goto fail;
}
BLKDBG_EVENT(bs->file, BLKDBG_L1_GROW_WRITE_TABLE);
for(i = 0; i < s->l1_size; i++)
new_l1_table[i] = cpu_to_be64(new_l1_table[i]);
ret = bdrv_pwrite_sync(bs->file, new_l1_table_offset,
new_l1_table, new_l1_size2);
if (ret < 0)
goto fail;
for(i = 0; i < s->l1_size; i++)
new_l1_table[i] = be64_to_cpu(new_l1_table[i]);
/* set new table */
BLKDBG_EVENT(bs->file, BLKDBG_L1_GROW_ACTIVATE_TABLE);
stl_be_p(data, new_l1_size);
stq_be_p(data + 4, new_l1_table_offset);
ret = bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, l1_size),
data, sizeof(data));
if (ret < 0) {
goto fail;
}
qemu_vfree(s->l1_table);
old_l1_table_offset = s->l1_table_offset;
s->l1_table_offset = new_l1_table_offset;
s->l1_table = new_l1_table;
old_l1_size = s->l1_size;
s->l1_size = new_l1_size;
qcow2_free_clusters(bs, old_l1_table_offset, old_l1_size * sizeof(uint64_t),
QCOW2_DISCARD_OTHER);
return 0;
fail:
qemu_vfree(new_l1_table);
qcow2_free_clusters(bs, new_l1_table_offset, new_l1_size2,
QCOW2_DISCARD_OTHER);
return ret;
}
/*
* l2_load
*
* @bs: The BlockDriverState
* @offset: A guest offset, used to calculate what slice of the L2
* table to load.
* @l2_offset: Offset to the L2 table in the image file.
* @l2_slice: Location to store the pointer to the L2 slice.
*
* Loads a L2 slice into memory (L2 slices are the parts of L2 tables
* that are loaded by the qcow2 cache). If the slice is in the cache,
* the cache is used; otherwise the L2 slice is loaded from the image
* file.
*/
static int l2_load(BlockDriverState *bs, uint64_t offset,
uint64_t l2_offset, uint64_t **l2_slice)
{
BDRVQcow2State *s = bs->opaque;
int start_of_slice = sizeof(uint64_t) *
(offset_to_l2_index(s, offset) - offset_to_l2_slice_index(s, offset));
return qcow2_cache_get(bs, s->l2_table_cache, l2_offset + start_of_slice,
(void **)l2_slice);
}
/*
* Writes one sector of the L1 table to the disk (can't update single entries
* and we really don't want bdrv_pread to perform a read-modify-write)
*/
#define L1_ENTRIES_PER_SECTOR (512 / 8)
int qcow2_write_l1_entry(BlockDriverState *bs, int l1_index)
{
BDRVQcow2State *s = bs->opaque;
uint64_t buf[L1_ENTRIES_PER_SECTOR] = { 0 };
int l1_start_index;
int i, ret;
l1_start_index = l1_index & ~(L1_ENTRIES_PER_SECTOR - 1);
for (i = 0; i < L1_ENTRIES_PER_SECTOR && l1_start_index + i < s->l1_size;
i++)
{
buf[i] = cpu_to_be64(s->l1_table[l1_start_index + i]);
}
ret = qcow2_pre_write_overlap_check(bs, QCOW2_OL_ACTIVE_L1,
s->l1_table_offset + 8 * l1_start_index, sizeof(buf), false);
if (ret < 0) {
return ret;
}
BLKDBG_EVENT(bs->file, BLKDBG_L1_UPDATE);
ret = bdrv_pwrite_sync(bs->file,
s->l1_table_offset + 8 * l1_start_index,
buf, sizeof(buf));
if (ret < 0) {
return ret;
}
return 0;
}
/*
* l2_allocate
*
* Allocate a new l2 entry in the file. If l1_index points to an already
* used entry in the L2 table (i.e. we are doing a copy on write for the L2
* table) copy the contents of the old L2 table into the newly allocated one.
* Otherwise the new table is initialized with zeros.
*
*/
static int l2_allocate(BlockDriverState *bs, int l1_index)
{
BDRVQcow2State *s = bs->opaque;
uint64_t old_l2_offset;
uint64_t *l2_slice = NULL;
unsigned slice, slice_size2, n_slices;
int64_t l2_offset;
int ret;
old_l2_offset = s->l1_table[l1_index];
trace_qcow2_l2_allocate(bs, l1_index);
/* allocate a new l2 entry */
l2_offset = qcow2_alloc_clusters(bs, s->l2_size * sizeof(uint64_t));
if (l2_offset < 0) {
ret = l2_offset;
goto fail;
}
/* The offset must fit in the offset field of the L1 table entry */
assert((l2_offset & L1E_OFFSET_MASK) == l2_offset);
/* If we're allocating the table at offset 0 then something is wrong */
if (l2_offset == 0) {
qcow2_signal_corruption(bs, true, -1, -1, "Preventing invalid "
"allocation of L2 table at offset 0");
ret = -EIO;
goto fail;
}
ret = qcow2_cache_flush(bs, s->refcount_block_cache);
if (ret < 0) {
goto fail;
}
/* allocate a new entry in the l2 cache */
slice_size2 = s->l2_slice_size * sizeof(uint64_t);
n_slices = s->cluster_size / slice_size2;
trace_qcow2_l2_allocate_get_empty(bs, l1_index);
for (slice = 0; slice < n_slices; slice++) {
ret = qcow2_cache_get_empty(bs, s->l2_table_cache,
l2_offset + slice * slice_size2,
(void **) &l2_slice);
if (ret < 0) {
goto fail;
}
if ((old_l2_offset & L1E_OFFSET_MASK) == 0) {
/* if there was no old l2 table, clear the new slice */
memset(l2_slice, 0, slice_size2);
} else {
uint64_t *old_slice;
uint64_t old_l2_slice_offset =
(old_l2_offset & L1E_OFFSET_MASK) + slice * slice_size2;
/* if there was an old l2 table, read a slice from the disk */
BLKDBG_EVENT(bs->file, BLKDBG_L2_ALLOC_COW_READ);
ret = qcow2_cache_get(bs, s->l2_table_cache, old_l2_slice_offset,
(void **) &old_slice);
if (ret < 0) {
goto fail;
}
memcpy(l2_slice, old_slice, slice_size2);
qcow2_cache_put(s->l2_table_cache, (void **) &old_slice);
}
/* write the l2 slice to the file */
BLKDBG_EVENT(bs->file, BLKDBG_L2_ALLOC_WRITE);
trace_qcow2_l2_allocate_write_l2(bs, l1_index);
qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice);
qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
}
ret = qcow2_cache_flush(bs, s->l2_table_cache);
if (ret < 0) {
goto fail;
}
/* update the L1 entry */
trace_qcow2_l2_allocate_write_l1(bs, l1_index);
s->l1_table[l1_index] = l2_offset | QCOW_OFLAG_COPIED;
ret = qcow2_write_l1_entry(bs, l1_index);
if (ret < 0) {
goto fail;
}
trace_qcow2_l2_allocate_done(bs, l1_index, 0);
return 0;
fail:
trace_qcow2_l2_allocate_done(bs, l1_index, ret);
if (l2_slice != NULL) {
qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
}
s->l1_table[l1_index] = old_l2_offset;
if (l2_offset > 0) {
qcow2_free_clusters(bs, l2_offset, s->l2_size * sizeof(uint64_t),
QCOW2_DISCARD_ALWAYS);
}
return ret;
}
/*
* Checks how many clusters in a given L2 slice are contiguous in the image
* file. As soon as one of the flags in the bitmask stop_flags changes compared
* to the first cluster, the search is stopped and the cluster is not counted
* as contiguous. (This allows it, for example, to stop at the first compressed
* cluster which may require a different handling)
*/
static int count_contiguous_clusters(BlockDriverState *bs, int nb_clusters,
int cluster_size, uint64_t *l2_slice, uint64_t stop_flags)
{
int i;
QCow2ClusterType first_cluster_type;
uint64_t mask = stop_flags | L2E_OFFSET_MASK | QCOW_OFLAG_COMPRESSED;
uint64_t first_entry = be64_to_cpu(l2_slice[0]);
uint64_t offset = first_entry & mask;
first_cluster_type = qcow2_get_cluster_type(bs, first_entry);
if (first_cluster_type == QCOW2_CLUSTER_UNALLOCATED) {
return 0;
}
/* must be allocated */
assert(first_cluster_type == QCOW2_CLUSTER_NORMAL ||
first_cluster_type == QCOW2_CLUSTER_ZERO_ALLOC);
for (i = 0; i < nb_clusters; i++) {
uint64_t l2_entry = be64_to_cpu(l2_slice[i]) & mask;
if (offset + (uint64_t) i * cluster_size != l2_entry) {
break;
}
}
return i;
}
/*
* Checks how many consecutive unallocated clusters in a given L2
* slice have the same cluster type.
*/
static int count_contiguous_clusters_unallocated(BlockDriverState *bs,
int nb_clusters,
uint64_t *l2_slice,
QCow2ClusterType wanted_type)
{
int i;
assert(wanted_type == QCOW2_CLUSTER_ZERO_PLAIN ||
wanted_type == QCOW2_CLUSTER_UNALLOCATED);
for (i = 0; i < nb_clusters; i++) {
uint64_t entry = be64_to_cpu(l2_slice[i]);
QCow2ClusterType type = qcow2_get_cluster_type(bs, entry);
if (type != wanted_type) {
break;
}
}
return i;
}
static int coroutine_fn do_perform_cow_read(BlockDriverState *bs,
uint64_t src_cluster_offset,
unsigned offset_in_cluster,
QEMUIOVector *qiov)
{
int ret;
if (qiov->size == 0) {
return 0;
}
BLKDBG_EVENT(bs->file, BLKDBG_COW_READ);
if (!bs->drv) {
return -ENOMEDIUM;
}
/* Call .bdrv_co_readv() directly instead of using the public block-layer
* interface. This avoids double I/O throttling and request tracking,
* which can lead to deadlock when block layer copy-on-read is enabled.
*/
ret = bs->drv->bdrv_co_preadv(bs, src_cluster_offset + offset_in_cluster,
qiov->size, qiov, 0);
if (ret < 0) {
return ret;
}
return 0;
}
static bool coroutine_fn do_perform_cow_encrypt(BlockDriverState *bs,
uint64_t src_cluster_offset,
uint64_t cluster_offset,
unsigned offset_in_cluster,
uint8_t *buffer,
unsigned bytes)
{
if (bytes && bs->encrypted) {
BDRVQcow2State *s = bs->opaque;
assert((offset_in_cluster & ~BDRV_SECTOR_MASK) == 0);
assert((bytes & ~BDRV_SECTOR_MASK) == 0);
assert(s->crypto);
if (qcow2_co_encrypt(bs, cluster_offset,
src_cluster_offset + offset_in_cluster,
buffer, bytes) < 0) {
return false;
}
}
return true;
}
static int coroutine_fn do_perform_cow_write(BlockDriverState *bs,
uint64_t cluster_offset,
unsigned offset_in_cluster,
QEMUIOVector *qiov)
{
BDRVQcow2State *s = bs->opaque;
int ret;
if (qiov->size == 0) {
return 0;
}
ret = qcow2_pre_write_overlap_check(bs, 0,
cluster_offset + offset_in_cluster, qiov->size, true);
if (ret < 0) {
return ret;
}
BLKDBG_EVENT(bs->file, BLKDBG_COW_WRITE);
ret = bdrv_co_pwritev(s->data_file, cluster_offset + offset_in_cluster,
qiov->size, qiov, 0);
if (ret < 0) {
return ret;
}
return 0;
}
/*
* get_cluster_offset
*
* For a given offset of the virtual disk, find the cluster type and offset in
* the qcow2 file. The offset is stored in *cluster_offset.
*
* On entry, *bytes is the maximum number of contiguous bytes starting at
* offset that we are interested in.
*
* On exit, *bytes is the number of bytes starting at offset that have the same
* cluster type and (if applicable) are stored contiguously in the image file.
* Compressed clusters are always returned one by one.
*
* Returns the cluster type (QCOW2_CLUSTER_*) on success, -errno in error
* cases.
*/
int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,
unsigned int *bytes, uint64_t *cluster_offset)
{
BDRVQcow2State *s = bs->opaque;
unsigned int l2_index;
uint64_t l1_index, l2_offset, *l2_slice;
int c;
unsigned int offset_in_cluster;
uint64_t bytes_available, bytes_needed, nb_clusters;
QCow2ClusterType type;
int ret;
offset_in_cluster = offset_into_cluster(s, offset);
bytes_needed = (uint64_t) *bytes + offset_in_cluster;
/* compute how many bytes there are between the start of the cluster
* containing offset and the end of the l2 slice that contains
* the entry pointing to it */
bytes_available =
((uint64_t) (s->l2_slice_size - offset_to_l2_slice_index(s, offset)))
<< s->cluster_bits;
if (bytes_needed > bytes_available) {
bytes_needed = bytes_available;
}
*cluster_offset = 0;
/* seek to the l2 offset in the l1 table */
l1_index = offset_to_l1_index(s, offset);
if (l1_index >= s->l1_size) {
type = QCOW2_CLUSTER_UNALLOCATED;
goto out;
}
l2_offset = s->l1_table[l1_index] & L1E_OFFSET_MASK;
if (!l2_offset) {
type = QCOW2_CLUSTER_UNALLOCATED;
goto out;
}
if (offset_into_cluster(s, l2_offset)) {
qcow2_signal_corruption(bs, true, -1, -1, "L2 table offset %#" PRIx64
" unaligned (L1 index: %#" PRIx64 ")",
l2_offset, l1_index);
return -EIO;
}
/* load the l2 slice in memory */
ret = l2_load(bs, offset, l2_offset, &l2_slice);
if (ret < 0) {
return ret;
}
/* find the cluster offset for the given disk offset */
l2_index = offset_to_l2_slice_index(s, offset);
*cluster_offset = be64_to_cpu(l2_slice[l2_index]);
nb_clusters = size_to_clusters(s, bytes_needed);
/* bytes_needed <= *bytes + offset_in_cluster, both of which are unsigned
* integers; the minimum cluster size is 512, so this assertion is always
* true */
assert(nb_clusters <= INT_MAX);
type = qcow2_get_cluster_type(bs, *cluster_offset);
if (s->qcow_version < 3 && (type == QCOW2_CLUSTER_ZERO_PLAIN ||
type == QCOW2_CLUSTER_ZERO_ALLOC)) {
qcow2_signal_corruption(bs, true, -1, -1, "Zero cluster entry found"
" in pre-v3 image (L2 offset: %#" PRIx64
", L2 index: %#x)", l2_offset, l2_index);
ret = -EIO;
goto fail;
}
switch (type) {
case QCOW2_CLUSTER_COMPRESSED:
if (has_data_file(bs)) {
qcow2_signal_corruption(bs, true, -1, -1, "Compressed cluster "
"entry found in image with external data "
"file (L2 offset: %#" PRIx64 ", L2 index: "
"%#x)", l2_offset, l2_index);
ret = -EIO;
goto fail;
}
/* Compressed clusters can only be processed one by one */
c = 1;
*cluster_offset &= L2E_COMPRESSED_OFFSET_SIZE_MASK;
break;
case QCOW2_CLUSTER_ZERO_PLAIN:
case QCOW2_CLUSTER_UNALLOCATED:
/* how many empty clusters ? */
c = count_contiguous_clusters_unallocated(bs, nb_clusters,
&l2_slice[l2_index], type);
*cluster_offset = 0;
break;
case QCOW2_CLUSTER_ZERO_ALLOC:
case QCOW2_CLUSTER_NORMAL:
/* how many allocated clusters ? */
c = count_contiguous_clusters(bs, nb_clusters, s->cluster_size,
&l2_slice[l2_index], QCOW_OFLAG_ZERO);
*cluster_offset &= L2E_OFFSET_MASK;
if (offset_into_cluster(s, *cluster_offset)) {
qcow2_signal_corruption(bs, true, -1, -1,
"Cluster allocation offset %#"
PRIx64 " unaligned (L2 offset: %#" PRIx64
", L2 index: %#x)", *cluster_offset,
l2_offset, l2_index);
ret = -EIO;
goto fail;
}
if (has_data_file(bs) && *cluster_offset != offset - offset_in_cluster)
{
qcow2_signal_corruption(bs, true, -1, -1,
"External data file host cluster offset %#"
PRIx64 " does not match guest cluster "
"offset: %#" PRIx64
", L2 index: %#x)", *cluster_offset,
offset - offset_in_cluster, l2_index);
ret = -EIO;
goto fail;
}
break;
default:
abort();
}
qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
bytes_available = (int64_t)c * s->cluster_size;
out:
if (bytes_available > bytes_needed) {
bytes_available = bytes_needed;
}
/* bytes_available <= bytes_needed <= *bytes + offset_in_cluster;
* subtracting offset_in_cluster will therefore definitely yield something
* not exceeding UINT_MAX */
assert(bytes_available - offset_in_cluster <= UINT_MAX);
*bytes = bytes_available - offset_in_cluster;
return type;
fail:
qcow2_cache_put(s->l2_table_cache, (void **)&l2_slice);
return ret;
}
/*
* get_cluster_table
*
* for a given disk offset, load (and allocate if needed)
* the appropriate slice of its l2 table.
*
* the cluster index in the l2 slice is given to the caller.
*
* Returns 0 on success, -errno in failure case
*/
static int get_cluster_table(BlockDriverState *bs, uint64_t offset,
uint64_t **new_l2_slice,
int *new_l2_index)
{
BDRVQcow2State *s = bs->opaque;
unsigned int l2_index;
uint64_t l1_index, l2_offset;
uint64_t *l2_slice = NULL;
int ret;
/* seek to the l2 offset in the l1 table */
l1_index = offset_to_l1_index(s, offset);
if (l1_index >= s->l1_size) {
ret = qcow2_grow_l1_table(bs, l1_index + 1, false);
if (ret < 0) {
return ret;
}
}
assert(l1_index < s->l1_size);
l2_offset = s->l1_table[l1_index] & L1E_OFFSET_MASK;
if (offset_into_cluster(s, l2_offset)) {
qcow2_signal_corruption(bs, true, -1, -1, "L2 table offset %#" PRIx64
" unaligned (L1 index: %#" PRIx64 ")",
l2_offset, l1_index);
return -EIO;
}
if (!(s->l1_table[l1_index] & QCOW_OFLAG_COPIED)) {
/* First allocate a new L2 table (and do COW if needed) */
ret = l2_allocate(bs, l1_index);
if (ret < 0) {
return ret;
}
/* Then decrease the refcount of the old table */
if (l2_offset) {
qcow2_free_clusters(bs, l2_offset, s->l2_size * sizeof(uint64_t),
QCOW2_DISCARD_OTHER);
}
/* Get the offset of the newly-allocated l2 table */
l2_offset = s->l1_table[l1_index] & L1E_OFFSET_MASK;
assert(offset_into_cluster(s, l2_offset) == 0);
}
/* load the l2 slice in memory */
ret = l2_load(bs, offset, l2_offset, &l2_slice);
if (ret < 0) {
return ret;
}
/* find the cluster offset for the given disk offset */
l2_index = offset_to_l2_slice_index(s, offset);
*new_l2_slice = l2_slice;
*new_l2_index = l2_index;
return 0;
}
/*
* alloc_compressed_cluster_offset
*
* For a given offset on the virtual disk, allocate a new compressed cluster
* and put the host offset of the cluster into *host_offset. If a cluster is
* already allocated at the offset, return an error.
*
* Return 0 on success and -errno in error cases
*/
int qcow2_alloc_compressed_cluster_offset(BlockDriverState *bs,
uint64_t offset,
int compressed_size,
uint64_t *host_offset)
{
BDRVQcow2State *s = bs->opaque;
int l2_index, ret;
uint64_t *l2_slice;
int64_t cluster_offset;
int nb_csectors;
if (has_data_file(bs)) {
return 0;
}
ret = get_cluster_table(bs, offset, &l2_slice, &l2_index);
if (ret < 0) {
return ret;
}
/* Compression can't overwrite anything. Fail if the cluster was already
* allocated. */
cluster_offset = be64_to_cpu(l2_slice[l2_index]);
if (cluster_offset & L2E_OFFSET_MASK) {
qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
return -EIO;
}
cluster_offset = qcow2_alloc_bytes(bs, compressed_size);
if (cluster_offset < 0) {
qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
return cluster_offset;
}
nb_csectors =
(cluster_offset + compressed_size - 1) / QCOW2_COMPRESSED_SECTOR_SIZE -
(cluster_offset / QCOW2_COMPRESSED_SECTOR_SIZE);
cluster_offset |= QCOW_OFLAG_COMPRESSED |
((uint64_t)nb_csectors << s->csize_shift);
/* update L2 table */
/* compressed clusters never have the copied flag */
BLKDBG_EVENT(bs->file, BLKDBG_L2_UPDATE_COMPRESSED);
qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice);
l2_slice[l2_index] = cpu_to_be64(cluster_offset);
qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
*host_offset = cluster_offset & s->cluster_offset_mask;
return 0;
}
static int perform_cow(BlockDriverState *bs, QCowL2Meta *m)
{
BDRVQcow2State *s = bs->opaque;
Qcow2COWRegion *start = &m->cow_start;
Qcow2COWRegion *end = &m->cow_end;
unsigned buffer_size;
unsigned data_bytes = end->offset - (start->offset + start->nb_bytes);
bool merge_reads;
uint8_t *start_buffer, *end_buffer;
QEMUIOVector qiov;
int ret;
assert(start->nb_bytes <= UINT_MAX - end->nb_bytes);
assert(start->nb_bytes + end->nb_bytes <= UINT_MAX - data_bytes);
assert(start->offset + start->nb_bytes <= end->offset);
assert(!m->data_qiov || m->data_qiov->size == data_bytes);
if ((start->nb_bytes == 0 && end->nb_bytes == 0) || m->skip_cow) {
return 0;
}
/* If we have to read both the start and end COW regions and the
* middle region is not too large then perform just one read
* operation */
merge_reads = start->nb_bytes && end->nb_bytes && data_bytes <= 16384;
if (merge_reads) {
buffer_size = start->nb_bytes + data_bytes + end->nb_bytes;
} else {
/* If we have to do two reads, add some padding in the middle
* if necessary to make sure that the end region is optimally
* aligned. */
size_t align = bdrv_opt_mem_align(bs);
assert(align > 0 && align <= UINT_MAX);
assert(QEMU_ALIGN_UP(start->nb_bytes, align) <=
UINT_MAX - end->nb_bytes);
buffer_size = QEMU_ALIGN_UP(start->nb_bytes, align) + end->nb_bytes;
}
/* Reserve a buffer large enough to store all the data that we're
* going to read */
start_buffer = qemu_try_blockalign(bs, buffer_size);
if (start_buffer == NULL) {
return -ENOMEM;
}
/* The part of the buffer where the end region is located */
end_buffer = start_buffer + buffer_size - end->nb_bytes;
qemu_iovec_init(&qiov, 2 + (m->data_qiov ? m->data_qiov->niov : 0));
qemu_co_mutex_unlock(&s->lock);
/* First we read the existing data from both COW regions. We
* either read the whole region in one go, or the start and end
* regions separately. */
if (merge_reads) {
qemu_iovec_add(&qiov, start_buffer, buffer_size);
ret = do_perform_cow_read(bs, m->offset, start->offset, &qiov);
} else {
qemu_iovec_add(&qiov, start_buffer, start->nb_bytes);
ret = do_perform_cow_read(bs, m->offset, start->offset, &qiov);
if (ret < 0) {
goto fail;
}
qemu_iovec_reset(&qiov);
qemu_iovec_add(&qiov, end_buffer, end->nb_bytes);
ret = do_perform_cow_read(bs, m->offset, end->offset, &qiov);
}
if (ret < 0) {
goto fail;
}
/* Encrypt the data if necessary before writing it */
if (bs->encrypted) {
if (!do_perform_cow_encrypt(bs, m->offset, m->alloc_offset,
start->offset, start_buffer,
start->nb_bytes) ||
!do_perform_cow_encrypt(bs, m->offset, m->alloc_offset,
end->offset, end_buffer, end->nb_bytes)) {
ret = -EIO;
goto fail;
}
}
/* And now we can write everything. If we have the guest data we
* can write everything in one single operation */
if (m->data_qiov) {
qemu_iovec_reset(&qiov);
if (start->nb_bytes) {
qemu_iovec_add(&qiov, start_buffer, start->nb_bytes);
}
qemu_iovec_concat(&qiov, m->data_qiov, 0, data_bytes);
if (end->nb_bytes) {
qemu_iovec_add(&qiov, end_buffer, end->nb_bytes);
}
/* NOTE: we have a write_aio blkdebug event here followed by
* a cow_write one in do_perform_cow_write(), but there's only
* one single I/O operation */
BLKDBG_EVENT(bs->file, BLKDBG_WRITE_AIO);
ret = do_perform_cow_write(bs, m->alloc_offset, start->offset, &qiov);
} else {
/* If there's no guest data then write both COW regions separately */
qemu_iovec_reset(&qiov);
qemu_iovec_add(&qiov, start_buffer, start->nb_bytes);
ret = do_perform_cow_write(bs, m->alloc_offset, start->offset, &qiov);
if (ret < 0) {
goto fail;
}
qemu_iovec_reset(&qiov);
qemu_iovec_add(&qiov, end_buffer, end->nb_bytes);
ret = do_perform_cow_write(bs, m->alloc_offset, end->offset, &qiov);
}
fail:
qemu_co_mutex_lock(&s->lock);
/*
* Before we update the L2 table to actually point to the new cluster, we
* need to be sure that the refcounts have been increased and COW was
* handled.
*/
if (ret == 0) {
qcow2_cache_depends_on_flush(s->l2_table_cache);
}
qemu_vfree(start_buffer);
qemu_iovec_destroy(&qiov);
return ret;
}
int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m)
{
BDRVQcow2State *s = bs->opaque;
int i, j = 0, l2_index, ret;
uint64_t *old_cluster, *l2_slice;
uint64_t cluster_offset = m->alloc_offset;
trace_qcow2_cluster_link_l2(qemu_coroutine_self(), m->nb_clusters);
assert(m->nb_clusters > 0);
old_cluster = g_try_new(uint64_t, m->nb_clusters);
if (old_cluster == NULL) {
ret = -ENOMEM;
goto err;
}
/* copy content of unmodified sectors */
ret = perform_cow(bs, m);
if (ret < 0) {
goto err;
}
/* Update L2 table. */
if (s->use_lazy_refcounts) {
qcow2_mark_dirty(bs);
}
if (qcow2_need_accurate_refcounts(s)) {
qcow2_cache_set_dependency(bs, s->l2_table_cache,
s->refcount_block_cache);
}
ret = get_cluster_table(bs, m->offset, &l2_slice, &l2_index);
if (ret < 0) {
goto err;
}
qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice);
assert(l2_index + m->nb_clusters <= s->l2_slice_size);
for (i = 0; i < m->nb_clusters; i++) {
/* if two concurrent writes happen to the same unallocated cluster
* each write allocates separate cluster and writes data concurrently.
* The first one to complete updates l2 table with pointer to its
* cluster the second one has to do RMW (which is done above by
* perform_cow()), update l2 table with its cluster pointer and free
* old cluster. This is what this loop does */
if (l2_slice[l2_index + i] != 0) {
old_cluster[j++] = l2_slice[l2_index + i];
}
l2_slice[l2_index + i] = cpu_to_be64((cluster_offset +
(i << s->cluster_bits)) | QCOW_OFLAG_COPIED);
}
qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
/*
* If this was a COW, we need to decrease the refcount of the old cluster.
*
* Don't discard clusters that reach a refcount of 0 (e.g. compressed
* clusters), the next write will reuse them anyway.
*/
if (!m->keep_old_clusters && j != 0) {
for (i = 0; i < j; i++) {
qcow2_free_any_clusters(bs, be64_to_cpu(old_cluster[i]), 1,
QCOW2_DISCARD_NEVER);
}
}
ret = 0;
err:
g_free(old_cluster);
return ret;
}
/**
* Frees the allocated clusters because the request failed and they won't
* actually be linked.
*/
void qcow2_alloc_cluster_abort(BlockDriverState *bs, QCowL2Meta *m)
{
BDRVQcow2State *s = bs->opaque;
qcow2_free_clusters(bs, m->alloc_offset, m->nb_clusters << s->cluster_bits,
QCOW2_DISCARD_NEVER);
}
/*
* Returns the number of contiguous clusters that can be used for an allocating
* write, but require COW to be performed (this includes yet unallocated space,
* which must copy from the backing file)
*/
static int count_cow_clusters(BlockDriverState *bs, int nb_clusters,
uint64_t *l2_slice, int l2_index)
{
int i;
for (i = 0; i < nb_clusters; i++) {
uint64_t l2_entry = be64_to_cpu(l2_slice[l2_index + i]);
QCow2ClusterType cluster_type = qcow2_get_cluster_type(bs, l2_entry);
switch(cluster_type) {
case QCOW2_CLUSTER_NORMAL:
if (l2_entry & QCOW_OFLAG_COPIED) {
goto out;
}
break;
case QCOW2_CLUSTER_UNALLOCATED:
case QCOW2_CLUSTER_COMPRESSED:
case QCOW2_CLUSTER_ZERO_PLAIN:
case QCOW2_CLUSTER_ZERO_ALLOC:
break;
default:
abort();
}
}
out:
assert(i <= nb_clusters);
return i;
}
/*
* Check if there already is an AIO write request in flight which allocates
* the same cluster. In this case we need to wait until the previous
* request has completed and updated the L2 table accordingly.
*
* Returns:
* 0 if there was no dependency. *cur_bytes indicates the number of
* bytes from guest_offset that can be read before the next
* dependency must be processed (or the request is complete)
*
* -EAGAIN if we had to wait for another request, previously gathered
* information on cluster allocation may be invalid now. The caller
* must start over anyway, so consider *cur_bytes undefined.
*/
static int handle_dependencies(BlockDriverState *bs, uint64_t guest_offset,
uint64_t *cur_bytes, QCowL2Meta **m)
{
BDRVQcow2State *s = bs->opaque;
QCowL2Meta *old_alloc;
uint64_t bytes = *cur_bytes;
QLIST_FOREACH(old_alloc, &s->cluster_allocs, next_in_flight) {
uint64_t start = guest_offset;
uint64_t end = start + bytes;
uint64_t old_start = l2meta_cow_start(old_alloc);
uint64_t old_end = l2meta_cow_end(old_alloc);
if (end <= old_start || start >= old_end) {
/* No intersection */
} else {
if (start < old_start) {
/* Stop at the start of a running allocation */
bytes = old_start - start;
} else {
bytes = 0;
}
/* Stop if already an l2meta exists. After yielding, it wouldn't
* be valid any more, so we'd have to clean up the old L2Metas
* and deal with requests depending on them before starting to
* gather new ones. Not worth the trouble. */
if (bytes == 0 && *m) {
*cur_bytes = 0;
return 0;
}
if (bytes == 0) {
/* Wait for the dependency to complete. We need to recheck
* the free/allocated clusters when we continue. */
qemu_co_queue_wait(&old_alloc->dependent_requests, &s->lock);
return -EAGAIN;
}
}
}
/* Make sure that existing clusters and new allocations are only used up to
* the next dependency if we shortened the request above */
*cur_bytes = bytes;
return 0;
}
/*
* Checks how many already allocated clusters that don't require a copy on
* write there are at the given guest_offset (up to *bytes). If *host_offset is
* not INV_OFFSET, only physically contiguous clusters beginning at this host
* offset are counted.
*
* Note that guest_offset may not be cluster aligned. In this case, the
* returned *host_offset points to exact byte referenced by guest_offset and
* therefore isn't cluster aligned as well.
*
* Returns:
* 0: if no allocated clusters are available at the given offset.
* *bytes is normally unchanged. It is set to 0 if the cluster
* is allocated and doesn't need COW, but doesn't have the right
* physical offset.
*
* 1: if allocated clusters that don't require a COW are available at
* the requested offset. *bytes may have decreased and describes
* the length of the area that can be written to.
*
* -errno: in error cases
*/
static int handle_copied(BlockDriverState *bs, uint64_t guest_offset,
uint64_t *host_offset, uint64_t *bytes, QCowL2Meta **m)
{
BDRVQcow2State *s = bs->opaque;
int l2_index;
uint64_t cluster_offset;
uint64_t *l2_slice;
uint64_t nb_clusters;
unsigned int keep_clusters;
int ret;
trace_qcow2_handle_copied(qemu_coroutine_self(), guest_offset, *host_offset,
*bytes);
assert(*host_offset == INV_OFFSET || offset_into_cluster(s, guest_offset)
== offset_into_cluster(s, *host_offset));
/*
* Calculate the number of clusters to look for. We stop at L2 slice
* boundaries to keep things simple.
*/
nb_clusters =
size_to_clusters(s, offset_into_cluster(s, guest_offset) + *bytes);
l2_index = offset_to_l2_slice_index(s, guest_offset);
nb_clusters = MIN(nb_clusters, s->l2_slice_size - l2_index);
assert(nb_clusters <= INT_MAX);
/* Find L2 entry for the first involved cluster */
ret = get_cluster_table(bs, guest_offset, &l2_slice, &l2_index);
if (ret < 0) {
return ret;
}
cluster_offset = be64_to_cpu(l2_slice[l2_index]);
/* Check how many clusters are already allocated and don't need COW */
if (qcow2_get_cluster_type(bs, cluster_offset) == QCOW2_CLUSTER_NORMAL
&& (cluster_offset & QCOW_OFLAG_COPIED))
{
/* If a specific host_offset is required, check it */
bool offset_matches =
(cluster_offset & L2E_OFFSET_MASK) == *host_offset;
if (offset_into_cluster(s, cluster_offset & L2E_OFFSET_MASK)) {
qcow2_signal_corruption(bs, true, -1, -1, "Data cluster offset "
"%#llx unaligned (guest offset: %#" PRIx64
")", cluster_offset & L2E_OFFSET_MASK,
guest_offset);
ret = -EIO;
goto out;
}
if (*host_offset != INV_OFFSET && !offset_matches) {
*bytes = 0;
ret = 0;
goto out;
}
/* We keep all QCOW_OFLAG_COPIED clusters */
keep_clusters =
count_contiguous_clusters(bs, nb_clusters, s->cluster_size,
&l2_slice[l2_index],
QCOW_OFLAG_COPIED | QCOW_OFLAG_ZERO);
assert(keep_clusters <= nb_clusters);
*bytes = MIN(*bytes,
keep_clusters * s->cluster_size
- offset_into_cluster(s, guest_offset));
ret = 1;
} else {
ret = 0;
}
/* Cleanup */
out:
qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
/* Only return a host offset if we actually made progress. Otherwise we
* would make requirements for handle_alloc() that it can't fulfill */
if (ret > 0) {
*host_offset = (cluster_offset & L2E_OFFSET_MASK)
+ offset_into_cluster(s, guest_offset);
}
return ret;
}
/*
* Allocates new clusters for the given guest_offset.
*
* At most *nb_clusters are allocated, and on return *nb_clusters is updated to
* contain the number of clusters that have been allocated and are contiguous
* in the image file.
*
* If *host_offset is not INV_OFFSET, it specifies the offset in the image file
* at which the new clusters must start. *nb_clusters can be 0 on return in
* this case if the cluster at host_offset is already in use. If *host_offset
* is INV_OFFSET, the clusters can be allocated anywhere in the image file.
*
* *host_offset is updated to contain the offset into the image file at which
* the first allocated cluster starts.
*
* Return 0 on success and -errno in error cases. -EAGAIN means that the
* function has been waiting for another request and the allocation must be
* restarted, but the whole request should not be failed.
*/
static int do_alloc_cluster_offset(BlockDriverState *bs, uint64_t guest_offset,
uint64_t *host_offset, uint64_t *nb_clusters)
{
BDRVQcow2State *s = bs->opaque;
trace_qcow2_do_alloc_clusters_offset(qemu_coroutine_self(), guest_offset,
*host_offset, *nb_clusters);
if (has_data_file(bs)) {
assert(*host_offset == INV_OFFSET ||
*host_offset == start_of_cluster(s, guest_offset));
*host_offset = start_of_cluster(s, guest_offset);
return 0;
}
/* Allocate new clusters */
trace_qcow2_cluster_alloc_phys(qemu_coroutine_self());
if (*host_offset == INV_OFFSET) {
int64_t cluster_offset =
qcow2_alloc_clusters(bs, *nb_clusters * s->cluster_size);
if (cluster_offset < 0) {
return cluster_offset;
}
*host_offset = cluster_offset;
return 0;
} else {
int64_t ret = qcow2_alloc_clusters_at(bs, *host_offset, *nb_clusters);
if (ret < 0) {
return ret;
}
*nb_clusters = ret;
return 0;
}
}
/*
* Allocates new clusters for an area that either is yet unallocated or needs a
* copy on write. If *host_offset is not INV_OFFSET, clusters are only
* allocated if the new allocation can match the specified host offset.
*
* Note that guest_offset may not be cluster aligned. In this case, the
* returned *host_offset points to exact byte referenced by guest_offset and
* therefore isn't cluster aligned as well.
*
* Returns:
* 0: if no clusters could be allocated. *bytes is set to 0,
* *host_offset is left unchanged.
*
* 1: if new clusters were allocated. *bytes may be decreased if the
* new allocation doesn't cover all of the requested area.
* *host_offset is updated to contain the host offset of the first
* newly allocated cluster.
*
* -errno: in error cases
*/
static int handle_alloc(BlockDriverState *bs, uint64_t guest_offset,
uint64_t *host_offset, uint64_t *bytes, QCowL2Meta **m)
{
BDRVQcow2State *s = bs->opaque;
int l2_index;
uint64_t *l2_slice;
uint64_t entry;
uint64_t nb_clusters;
int ret;
bool keep_old_clusters = false;
uint64_t alloc_cluster_offset = INV_OFFSET;
trace_qcow2_handle_alloc(qemu_coroutine_self(), guest_offset, *host_offset,
*bytes);
assert(*bytes > 0);
/*
* Calculate the number of clusters to look for. We stop at L2 slice
* boundaries to keep things simple.
*/
nb_clusters =
size_to_clusters(s, offset_into_cluster(s, guest_offset) + *bytes);
l2_index = offset_to_l2_slice_index(s, guest_offset);
nb_clusters = MIN(nb_clusters, s->l2_slice_size - l2_index);
assert(nb_clusters <= INT_MAX);
/* Find L2 entry for the first involved cluster */
ret = get_cluster_table(bs, guest_offset, &l2_slice, &l2_index);
if (ret < 0) {
return ret;
}
entry = be64_to_cpu(l2_slice[l2_index]);
/* For the moment, overwrite compressed clusters one by one */
if (entry & QCOW_OFLAG_COMPRESSED) {
nb_clusters = 1;
} else {
nb_clusters = count_cow_clusters(bs, nb_clusters, l2_slice, l2_index);
}
/* This function is only called when there were no non-COW clusters, so if
* we can't find any unallocated or COW clusters either, something is
* wrong with our code. */
assert(nb_clusters > 0);
if (qcow2_get_cluster_type(bs, entry) == QCOW2_CLUSTER_ZERO_ALLOC &&
(entry & QCOW_OFLAG_COPIED) &&
(*host_offset == INV_OFFSET ||
start_of_cluster(s, *host_offset) == (entry & L2E_OFFSET_MASK)))
{
int preallocated_nb_clusters;
if (offset_into_cluster(s, entry & L2E_OFFSET_MASK)) {
qcow2_signal_corruption(bs, true, -1, -1, "Preallocated zero "
"cluster offset %#llx unaligned (guest "
"offset: %#" PRIx64 ")",
entry & L2E_OFFSET_MASK, guest_offset);
ret = -EIO;
goto fail;
}
/* Try to reuse preallocated zero clusters; contiguous normal clusters
* would be fine, too, but count_cow_clusters() above has limited
* nb_clusters already to a range of COW clusters */
preallocated_nb_clusters =
count_contiguous_clusters(bs, nb_clusters, s->cluster_size,
&l2_slice[l2_index], QCOW_OFLAG_COPIED);
assert(preallocated_nb_clusters > 0);
nb_clusters = preallocated_nb_clusters;
alloc_cluster_offset = entry & L2E_OFFSET_MASK;
/* We want to reuse these clusters, so qcow2_alloc_cluster_link_l2()
* should not free them. */
keep_old_clusters = true;
}
qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
if (alloc_cluster_offset == INV_OFFSET) {
/* Allocate, if necessary at a given offset in the image file */
alloc_cluster_offset = *host_offset == INV_OFFSET ? INV_OFFSET :
start_of_cluster(s, *host_offset);
ret = do_alloc_cluster_offset(bs, guest_offset, &alloc_cluster_offset,
&nb_clusters);
if (ret < 0) {
goto fail;
}
/* Can't extend contiguous allocation */
if (nb_clusters == 0) {
*bytes = 0;
return 0;
}
assert(alloc_cluster_offset != INV_OFFSET);
}
/*
* Save info needed for meta data update.
*
* requested_bytes: Number of bytes from the start of the first
* newly allocated cluster to the end of the (possibly shortened
* before) write request.
*
* avail_bytes: Number of bytes from the start of the first
* newly allocated to the end of the last newly allocated cluster.
*
* nb_bytes: The number of bytes from the start of the first
* newly allocated cluster to the end of the area that the write
* request actually writes to (excluding COW at the end)
*/
uint64_t requested_bytes = *bytes + offset_into_cluster(s, guest_offset);
int avail_bytes = MIN(INT_MAX, nb_clusters << s->cluster_bits);
int nb_bytes = MIN(requested_bytes, avail_bytes);
QCowL2Meta *old_m = *m;
*m = g_malloc0(sizeof(**m));
**m = (QCowL2Meta) {
.next = old_m,
.alloc_offset = alloc_cluster_offset,
.offset = start_of_cluster(s, guest_offset),
.nb_clusters = nb_clusters,
.keep_old_clusters = keep_old_clusters,
.cow_start = {
.offset = 0,
.nb_bytes = offset_into_cluster(s, guest_offset),
},
.cow_end = {
.offset = nb_bytes,
.nb_bytes = avail_bytes - nb_bytes,
},
};
qemu_co_queue_init(&(*m)->dependent_requests);
QLIST_INSERT_HEAD(&s->cluster_allocs, *m, next_in_flight);
*host_offset = alloc_cluster_offset + offset_into_cluster(s, guest_offset);
*bytes = MIN(*bytes, nb_bytes - offset_into_cluster(s, guest_offset));
assert(*bytes != 0);
return 1;
fail:
if (*m && (*m)->nb_clusters > 0) {
QLIST_REMOVE(*m, next_in_flight);
}
return ret;
}
/*
* alloc_cluster_offset
*
* For a given offset on the virtual disk, find the cluster offset in qcow2
* file. If the offset is not found, allocate a new cluster.
*
* If the cluster was already allocated, m->nb_clusters is set to 0 and
* other fields in m are meaningless.
*
* If the cluster is newly allocated, m->nb_clusters is set to the number of
* contiguous clusters that have been allocated. In this case, the other
* fields of m are valid and contain information about the first allocated
* cluster.
*
* If the request conflicts with another write request in flight, the coroutine
* is queued and will be reentered when the dependency has completed.
*
* Return 0 on success and -errno in error cases
*/
int qcow2_alloc_cluster_offset(BlockDriverState *bs, uint64_t offset,
unsigned int *bytes, uint64_t *host_offset,
QCowL2Meta **m)
{
BDRVQcow2State *s = bs->opaque;
uint64_t start, remaining;
uint64_t cluster_offset;
uint64_t cur_bytes;
int ret;
trace_qcow2_alloc_clusters_offset(qemu_coroutine_self(), offset, *bytes);
again:
start = offset;
remaining = *bytes;
cluster_offset = INV_OFFSET;
*host_offset = INV_OFFSET;
cur_bytes = 0;
*m = NULL;
while (true) {
if (*host_offset == INV_OFFSET && cluster_offset != INV_OFFSET) {
*host_offset = start_of_cluster(s, cluster_offset);
}
assert(remaining >= cur_bytes);
start += cur_bytes;
remaining -= cur_bytes;
if (cluster_offset != INV_OFFSET) {
cluster_offset += cur_bytes;
}
if (remaining == 0) {
break;
}
cur_bytes = remaining;
/*
* Now start gathering as many contiguous clusters as possible:
*
* 1. Check for overlaps with in-flight allocations
*
* a) Overlap not in the first cluster -> shorten this request and
* let the caller handle the rest in its next loop iteration.
*
* b) Real overlaps of two requests. Yield and restart the search
* for contiguous clusters (the situation could have changed
* while we were sleeping)
*
* c) TODO: Request starts in the same cluster as the in-flight
* allocation ends. Shorten the COW of the in-fight allocation,
* set cluster_offset to write to the same cluster and set up
* the right synchronisation between the in-flight request and
* the new one.
*/
ret = handle_dependencies(bs, start, &cur_bytes, m);
if (ret == -EAGAIN) {
/* Currently handle_dependencies() doesn't yield if we already had
* an allocation. If it did, we would have to clean up the L2Meta
* structs before starting over. */
assert(*m == NULL);
goto again;
} else if (ret < 0) {
return ret;
} else if (cur_bytes == 0) {
break;
} else {
/* handle_dependencies() may have decreased cur_bytes (shortened
* the allocations below) so that the next dependency is processed
* correctly during the next loop iteration. */
}
/*
* 2. Count contiguous COPIED clusters.
*/
ret = handle_copied(bs, start, &cluster_offset, &cur_bytes, m);
if (ret < 0) {
return ret;
} else if (ret) {
continue;
} else if (cur_bytes == 0) {
break;
}
/*
* 3. If the request still hasn't completed, allocate new clusters,
* considering any cluster_offset of steps 1c or 2.
*/
ret = handle_alloc(bs, start, &cluster_offset, &cur_bytes, m);
if (ret < 0) {
return ret;
} else if (ret) {
continue;
} else {
assert(cur_bytes == 0);
break;
}
}
*bytes -= remaining;
assert(*bytes > 0);
assert(*host_offset != INV_OFFSET);
return 0;
}
/*
* This discards as many clusters of nb_clusters as possible at once (i.e.
* all clusters in the same L2 slice) and returns the number of discarded
* clusters.
*/
static int discard_in_l2_slice(BlockDriverState *bs, uint64_t offset,
uint64_t nb_clusters,
enum qcow2_discard_type type, bool full_discard)
{
BDRVQcow2State *s = bs->opaque;
uint64_t *l2_slice;
int l2_index;
int ret;
int i;
ret = get_cluster_table(bs, offset, &l2_slice, &l2_index);
if (ret < 0) {
return ret;
}
/* Limit nb_clusters to one L2 slice */
nb_clusters = MIN(nb_clusters, s->l2_slice_size - l2_index);
assert(nb_clusters <= INT_MAX);
for (i = 0; i < nb_clusters; i++) {
uint64_t old_l2_entry;
old_l2_entry = be64_to_cpu(l2_slice[l2_index + i]);
/*
* If full_discard is false, make sure that a discarded area reads back
* as zeroes for v3 images (we cannot do it for v2 without actually
* writing a zero-filled buffer). We can skip the operation if the
* cluster is already marked as zero, or if it's unallocated and we
* don't have a backing file.
*
* TODO We might want to use bdrv_block_status(bs) here, but we're
* holding s->lock, so that doesn't work today.
*
* If full_discard is true, the sector should not read back as zeroes,
* but rather fall through to the backing file.
*/
switch (qcow2_get_cluster_type(bs, old_l2_entry)) {
case QCOW2_CLUSTER_UNALLOCATED:
if (full_discard || !bs->backing) {
continue;
}
break;
case QCOW2_CLUSTER_ZERO_PLAIN:
if (!full_discard) {
continue;
}
break;
case QCOW2_CLUSTER_ZERO_ALLOC:
case QCOW2_CLUSTER_NORMAL:
case QCOW2_CLUSTER_COMPRESSED:
break;
default:
abort();
}
/* First remove L2 entries */
qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice);
if (!full_discard && s->qcow_version >= 3) {
l2_slice[l2_index + i] = cpu_to_be64(QCOW_OFLAG_ZERO);
} else {
l2_slice[l2_index + i] = cpu_to_be64(0);
}
/* Then decrease the refcount */
qcow2_free_any_clusters(bs, old_l2_entry, 1, type);
}
qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
return nb_clusters;
}
int qcow2_cluster_discard(BlockDriverState *bs, uint64_t offset,
uint64_t bytes, enum qcow2_discard_type type,
bool full_discard)
{
BDRVQcow2State *s = bs->opaque;
uint64_t end_offset = offset + bytes;
uint64_t nb_clusters;
int64_t cleared;
int ret;
/* Caller must pass aligned values, except at image end */
assert(QEMU_IS_ALIGNED(offset, s->cluster_size));
assert(QEMU_IS_ALIGNED(end_offset, s->cluster_size) ||
end_offset == bs->total_sectors << BDRV_SECTOR_BITS);
nb_clusters = size_to_clusters(s, bytes);
s->cache_discards = true;
/* Each L2 slice is handled by its own loop iteration */
while (nb_clusters > 0) {
cleared = discard_in_l2_slice(bs, offset, nb_clusters, type,
full_discard);
if (cleared < 0) {
ret = cleared;
goto fail;
}
nb_clusters -= cleared;
offset += (cleared * s->cluster_size);
}
ret = 0;
fail:
s->cache_discards = false;
qcow2_process_discards(bs, ret);
return ret;
}
/*
* This zeroes as many clusters of nb_clusters as possible at once (i.e.
* all clusters in the same L2 slice) and returns the number of zeroed
* clusters.
*/
static int zero_in_l2_slice(BlockDriverState *bs, uint64_t offset,
uint64_t nb_clusters, int flags)
{
BDRVQcow2State *s = bs->opaque;
uint64_t *l2_slice;
int l2_index;
int ret;
int i;
bool unmap = !!(flags & BDRV_REQ_MAY_UNMAP);
ret = get_cluster_table(bs, offset, &l2_slice, &l2_index);
if (ret < 0) {
return ret;
}
/* Limit nb_clusters to one L2 slice */
nb_clusters = MIN(nb_clusters, s->l2_slice_size - l2_index);
assert(nb_clusters <= INT_MAX);
for (i = 0; i < nb_clusters; i++) {
uint64_t old_offset;
QCow2ClusterType cluster_type;
old_offset = be64_to_cpu(l2_slice[l2_index + i]);
/*
* Minimize L2 changes if the cluster already reads back as
* zeroes with correct allocation.
*/
cluster_type = qcow2_get_cluster_type(bs, old_offset);
if (cluster_type == QCOW2_CLUSTER_ZERO_PLAIN ||
(cluster_type == QCOW2_CLUSTER_ZERO_ALLOC && !unmap)) {
continue;
}
qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice);
if (cluster_type == QCOW2_CLUSTER_COMPRESSED || unmap) {
l2_slice[l2_index + i] = cpu_to_be64(QCOW_OFLAG_ZERO);
qcow2_free_any_clusters(bs, old_offset, 1, QCOW2_DISCARD_REQUEST);
} else {
l2_slice[l2_index + i] |= cpu_to_be64(QCOW_OFLAG_ZERO);
}
}
qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
return nb_clusters;
}
int qcow2_cluster_zeroize(BlockDriverState *bs, uint64_t offset,
uint64_t bytes, int flags)
{
BDRVQcow2State *s = bs->opaque;
uint64_t end_offset = offset + bytes;
uint64_t nb_clusters;
int64_t cleared;
int ret;
/* If we have to stay in sync with an external data file, zero out
* s->data_file first. */
if (data_file_is_raw(bs)) {
assert(has_data_file(bs));
ret = bdrv_co_pwrite_zeroes(s->data_file, offset, bytes, flags);
if (ret < 0) {
return ret;
}
}
/* Caller must pass aligned values, except at image end */
assert(QEMU_IS_ALIGNED(offset, s->cluster_size));
assert(QEMU_IS_ALIGNED(end_offset, s->cluster_size) ||
end_offset == bs->total_sectors << BDRV_SECTOR_BITS);
/* The zero flag is only supported by version 3 and newer */
if (s->qcow_version < 3) {
return -ENOTSUP;
}
/* Each L2 slice is handled by its own loop iteration */
nb_clusters = size_to_clusters(s, bytes);
s->cache_discards = true;
while (nb_clusters > 0) {
cleared = zero_in_l2_slice(bs, offset, nb_clusters, flags);
if (cleared < 0) {
ret = cleared;
goto fail;
}
nb_clusters -= cleared;
offset += (cleared * s->cluster_size);
}
ret = 0;
fail:
s->cache_discards = false;
qcow2_process_discards(bs, ret);
return ret;
}
/*
* Expands all zero clusters in a specific L1 table (or deallocates them, for
* non-backed non-pre-allocated zero clusters).
*
* l1_entries and *visited_l1_entries are used to keep track of progress for
* status_cb(). l1_entries contains the total number of L1 entries and
* *visited_l1_entries counts all visited L1 entries.
*/
static int expand_zero_clusters_in_l1(BlockDriverState *bs, uint64_t *l1_table,
int l1_size, int64_t *visited_l1_entries,
int64_t l1_entries,
BlockDriverAmendStatusCB *status_cb,
void *cb_opaque)
{
BDRVQcow2State *s = bs->opaque;
bool is_active_l1 = (l1_table == s->l1_table);
uint64_t *l2_slice = NULL;
unsigned slice, slice_size2, n_slices;
int ret;
int i, j;
slice_size2 = s->l2_slice_size * sizeof(uint64_t);
n_slices = s->cluster_size / slice_size2;
if (!is_active_l1) {
/* inactive L2 tables require a buffer to be stored in when loading
* them from disk */
l2_slice = qemu_try_blockalign(bs->file->bs, slice_size2);
if (l2_slice == NULL) {
return -ENOMEM;
}
}
for (i = 0; i < l1_size; i++) {
uint64_t l2_offset = l1_table[i] & L1E_OFFSET_MASK;
uint64_t l2_refcount;
if (!l2_offset) {
/* unallocated */
(*visited_l1_entries)++;
if (status_cb) {
status_cb(bs, *visited_l1_entries, l1_entries, cb_opaque);
}
continue;
}
if (offset_into_cluster(s, l2_offset)) {
qcow2_signal_corruption(bs, true, -1, -1, "L2 table offset %#"
PRIx64 " unaligned (L1 index: %#x)",
l2_offset, i);
ret = -EIO;
goto fail;
}
ret = qcow2_get_refcount(bs, l2_offset >> s->cluster_bits,
&l2_refcount);
if (ret < 0) {
goto fail;
}
for (slice = 0; slice < n_slices; slice++) {
uint64_t slice_offset = l2_offset + slice * slice_size2;
bool l2_dirty = false;
if (is_active_l1) {
/* get active L2 tables from cache */
ret = qcow2_cache_get(bs, s->l2_table_cache, slice_offset,
(void **)&l2_slice);
} else {
/* load inactive L2 tables from disk */
ret = bdrv_pread(bs->file, slice_offset, l2_slice, slice_size2);
}
if (ret < 0) {
goto fail;
}
for (j = 0; j < s->l2_slice_size; j++) {
uint64_t l2_entry = be64_to_cpu(l2_slice[j]);
int64_t offset = l2_entry & L2E_OFFSET_MASK;
QCow2ClusterType cluster_type =
qcow2_get_cluster_type(bs, l2_entry);
if (cluster_type != QCOW2_CLUSTER_ZERO_PLAIN &&
cluster_type != QCOW2_CLUSTER_ZERO_ALLOC) {
continue;
}
if (cluster_type == QCOW2_CLUSTER_ZERO_PLAIN) {
if (!bs->backing) {
/* not backed; therefore we can simply deallocate the
* cluster */
l2_slice[j] = 0;
l2_dirty = true;
continue;
}
offset = qcow2_alloc_clusters(bs, s->cluster_size);
if (offset < 0) {
ret = offset;
goto fail;
}
if (l2_refcount > 1) {
/* For shared L2 tables, set the refcount accordingly
* (it is already 1 and needs to be l2_refcount) */
ret = qcow2_update_cluster_refcount(
bs, offset >> s->cluster_bits,
refcount_diff(1, l2_refcount), false,
QCOW2_DISCARD_OTHER);
if (ret < 0) {
qcow2_free_clusters(bs, offset, s->cluster_size,
QCOW2_DISCARD_OTHER);
goto fail;
}
}
}
if (offset_into_cluster(s, offset)) {
int l2_index = slice * s->l2_slice_size + j;
qcow2_signal_corruption(
bs, true, -1, -1,
"Cluster allocation offset "
"%#" PRIx64 " unaligned (L2 offset: %#"
PRIx64 ", L2 index: %#x)", offset,
l2_offset, l2_index);
if (cluster_type == QCOW2_CLUSTER_ZERO_PLAIN) {
qcow2_free_clusters(bs, offset, s->cluster_size,
QCOW2_DISCARD_ALWAYS);
}
ret = -EIO;
goto fail;
}
ret = qcow2_pre_write_overlap_check(bs, 0, offset,
s->cluster_size, true);
if (ret < 0) {
if (cluster_type == QCOW2_CLUSTER_ZERO_PLAIN) {
qcow2_free_clusters(bs, offset, s->cluster_size,
QCOW2_DISCARD_ALWAYS);
}
goto fail;
}
ret = bdrv_pwrite_zeroes(s->data_file, offset,
s->cluster_size, 0);
if (ret < 0) {
if (cluster_type == QCOW2_CLUSTER_ZERO_PLAIN) {
qcow2_free_clusters(bs, offset, s->cluster_size,
QCOW2_DISCARD_ALWAYS);
}
goto fail;
}
if (l2_refcount == 1) {
l2_slice[j] = cpu_to_be64(offset | QCOW_OFLAG_COPIED);
} else {
l2_slice[j] = cpu_to_be64(offset);
}
l2_dirty = true;
}
if (is_active_l1) {
if (l2_dirty) {
qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice);
qcow2_cache_depends_on_flush(s->l2_table_cache);
}
qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
} else {
if (l2_dirty) {
ret = qcow2_pre_write_overlap_check(
bs, QCOW2_OL_INACTIVE_L2 | QCOW2_OL_ACTIVE_L2,
slice_offset, slice_size2, false);
if (ret < 0) {
goto fail;
}
ret = bdrv_pwrite(bs->file, slice_offset,
l2_slice, slice_size2);
if (ret < 0) {
goto fail;
}
}
}
}
(*visited_l1_entries)++;
if (status_cb) {
status_cb(bs, *visited_l1_entries, l1_entries, cb_opaque);
}
}
ret = 0;
fail:
if (l2_slice) {
if (!is_active_l1) {
qemu_vfree(l2_slice);
} else {
qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
}
}
return ret;
}
/*
* For backed images, expands all zero clusters on the image. For non-backed
* images, deallocates all non-pre-allocated zero clusters (and claims the
* allocation for pre-allocated ones). This is important for downgrading to a
* qcow2 version which doesn't yet support metadata zero clusters.
*/
int qcow2_expand_zero_clusters(BlockDriverState *bs,
BlockDriverAmendStatusCB *status_cb,
void *cb_opaque)
{
BDRVQcow2State *s = bs->opaque;
uint64_t *l1_table = NULL;
int64_t l1_entries = 0, visited_l1_entries = 0;
int ret;
int i, j;
if (status_cb) {
l1_entries = s->l1_size;
for (i = 0; i < s->nb_snapshots; i++) {
l1_entries += s->snapshots[i].l1_size;
}
}
ret = expand_zero_clusters_in_l1(bs, s->l1_table, s->l1_size,
&visited_l1_entries, l1_entries,
status_cb, cb_opaque);
if (ret < 0) {
goto fail;
}
/* Inactive L1 tables may point to active L2 tables - therefore it is
* necessary to flush the L2 table cache before trying to access the L2
* tables pointed to by inactive L1 entries (else we might try to expand
* zero clusters that have already been expanded); furthermore, it is also
* necessary to empty the L2 table cache, since it may contain tables which
* are now going to be modified directly on disk, bypassing the cache.
* qcow2_cache_empty() does both for us. */
ret = qcow2_cache_empty(bs, s->l2_table_cache);
if (ret < 0) {
goto fail;
}
for (i = 0; i < s->nb_snapshots; i++) {
int l1_size2;
uint64_t *new_l1_table;
Error *local_err = NULL;
ret = qcow2_validate_table(bs, s->snapshots[i].l1_table_offset,
s->snapshots[i].l1_size, sizeof(uint64_t),
QCOW_MAX_L1_SIZE, "Snapshot L1 table",
&local_err);
if (ret < 0) {
error_report_err(local_err);
goto fail;
}
l1_size2 = s->snapshots[i].l1_size * sizeof(uint64_t);
new_l1_table = g_try_realloc(l1_table, l1_size2);
if (!new_l1_table) {
ret = -ENOMEM;
goto fail;
}
l1_table = new_l1_table;
ret = bdrv_pread(bs->file, s->snapshots[i].l1_table_offset,
l1_table, l1_size2);
if (ret < 0) {
goto fail;
}
for (j = 0; j < s->snapshots[i].l1_size; j++) {
be64_to_cpus(&l1_table[j]);
}
ret = expand_zero_clusters_in_l1(bs, l1_table, s->snapshots[i].l1_size,
&visited_l1_entries, l1_entries,
status_cb, cb_opaque);
if (ret < 0) {
goto fail;
}
}
ret = 0;
fail:
g_free(l1_table);
return ret;
}
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