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qcow2: Introduce Qcow2COWRegion

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This makes it easier to address the areas for which a COW must be
performed. As a nice side effect, the COW code in
qcow2_alloc_cluster_link_l2 becomes really trivial.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Kevin Wolf 2012-12-07 18:08:43 +01:00
parent 1d3afd649b
commit 593fb83cac
2 changed files with 76 additions and 36 deletions
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83
block/qcow2-cluster.c
View File

@ -615,13 +615,41 @@ uint64_t qcow2_alloc_compressed_cluster_offset(BlockDriverState *bs,
return cluster_offset;
}
static int perform_cow(BlockDriverState *bs, QCowL2Meta *m, Qcow2COWRegion *r)
{
BDRVQcowState *s = bs->opaque;
int ret;
if (r->nb_sectors == 0) {
return 0;
}
qemu_co_mutex_unlock(&s->lock);
ret = copy_sectors(bs, m->offset / BDRV_SECTOR_SIZE, m->alloc_offset,
r->offset / BDRV_SECTOR_SIZE,
r->offset / BDRV_SECTOR_SIZE + r->nb_sectors);
qemu_co_mutex_lock(&s->lock);
if (ret < 0) {
return ret;
}
/*
* 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.
*/
qcow2_cache_depends_on_flush(s->l2_table_cache);
return 0;
}
int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m)
{
BDRVQcowState *s = bs->opaque;
int i, j = 0, l2_index, ret;
uint64_t *old_cluster, start_sect, *l2_table;
uint64_t *old_cluster, *l2_table;
uint64_t cluster_offset = m->alloc_offset;
bool cow = false;
trace_qcow2_cluster_link_l2(qemu_coroutine_self(), m->nb_clusters);
@ -631,36 +659,17 @@ int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m)
old_cluster = g_malloc(m->nb_clusters * sizeof(uint64_t));
/* copy content of unmodified sectors */
start_sect = m->offset >> 9;
if (m->n_start) {
cow = true;
qemu_co_mutex_unlock(&s->lock);
ret = copy_sectors(bs, start_sect, cluster_offset, 0, m->n_start);
qemu_co_mutex_lock(&s->lock);
if (ret < 0)
goto err;
ret = perform_cow(bs, m, &m->cow_start);
if (ret < 0) {
goto err;
}
if (m->nb_available & (s->cluster_sectors - 1)) {
cow = true;
qemu_co_mutex_unlock(&s->lock);
ret = copy_sectors(bs, start_sect, cluster_offset, m->nb_available,
align_offset(m->nb_available, s->cluster_sectors));
qemu_co_mutex_lock(&s->lock);
if (ret < 0)
goto err;
ret = perform_cow(bs, m, &m->cow_end);
if (ret < 0) {
goto err;
}
/*
* Update L2 table.
*
* 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 (cow) {
qcow2_cache_depends_on_flush(s->l2_table_cache);
}
/* Update L2 table. */
if (qcow2_need_accurate_refcounts(s)) {
qcow2_cache_set_dependency(bs, s->l2_table_cache,
@ -957,19 +966,33 @@ again:
*
* avail_sectors: Number of sectors from the start of the first
* newly allocated to the end of the last newly allocated cluster.
*
* nb_sectors: The number of sectors from the start of the first
* newly allocated cluster to the end of the aread that the write
* request actually writes to (excluding COW at the end)
*/
int requested_sectors = n_end - keep_clusters * s->cluster_sectors;
int avail_sectors = nb_clusters
<< (s->cluster_bits - BDRV_SECTOR_BITS);
int alloc_n_start = keep_clusters == 0 ? n_start : 0;
int nb_sectors = MIN(requested_sectors, avail_sectors);
*m = (QCowL2Meta) {
.cluster_offset = keep_clusters == 0 ?
alloc_cluster_offset : cluster_offset,
.alloc_offset = alloc_cluster_offset,
.offset = alloc_offset & ~(s->cluster_size - 1),
.n_start = keep_clusters == 0 ? n_start : 0,
.nb_clusters = nb_clusters,
.nb_available = MIN(requested_sectors, avail_sectors),
.nb_available = nb_sectors,
.cow_start = {
.offset = 0,
.nb_sectors = alloc_n_start,
},
.cow_end = {
.offset = nb_sectors * BDRV_SECTOR_SIZE,
.nb_sectors = avail_sectors - nb_sectors,
},
};
qemu_co_queue_init(&m->dependent_requests);
QLIST_INSERT_HEAD(&s->cluster_allocs, m, next_in_flight);

29
block/qcow2.h
View File

@ -196,6 +196,17 @@ typedef struct QCowCreateState {
struct QCowAIOCB;
typedef struct Qcow2COWRegion {
/**
* Offset of the COW region in bytes from the start of the first cluster
* touched by the request.
*/
uint64_t offset;
/** Number of sectors to copy */
int nb_sectors;
} Qcow2COWRegion;
/* XXX This could be private for qcow2-cluster.c */
typedef struct QCowL2Meta
{
@ -208,12 +219,6 @@ typedef struct QCowL2Meta
/** Host offset of the first newly allocated cluster */
uint64_t alloc_offset;
/**
* Number of sectors between the start of the first allocated cluster and
* the area that the guest actually writes to.
*/
int n_start;
/**
* Number of sectors from the start of the first allocated cluster to
* the end of the (possibly shortened) request
@ -229,6 +234,18 @@ typedef struct QCowL2Meta
*/
CoQueue dependent_requests;
/**
* The COW Region between the start of the first allocated cluster and the
* area the guest actually writes to.
*/
Qcow2COWRegion cow_start;
/**
* The COW Region between the area the guest actually writes to and the
* end of the last allocated cluster.
*/
Qcow2COWRegion cow_end;
QLIST_ENTRY(QCowL2Meta) next_in_flight;
} QCowL2Meta;