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qcow2: extract preallocation calculation function

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Calculating the preallocated image size will be needed to implement
.bdrv_measure().  Extract the code out into a separate function.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-id: 20170705125738.8777-4-stefanha@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2017-07-05 13:57:32 +01:00 committed by Max Reitz
parent a843a22a82
commit 95c67e3bd7
1 changed files with 77 additions and 59 deletions
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136
block/qcow2.c
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@ -2537,6 +2537,80 @@ static int preallocate(BlockDriverState *bs)
return 0;
}
/**
* qcow2_calc_prealloc_size:
* @total_size: virtual disk size in bytes
* @cluster_size: cluster size in bytes
* @refcount_order: refcount bits power-of-2 exponent
*
* Returns: Total number of bytes required for the fully allocated image
* (including metadata).
*/
static int64_t qcow2_calc_prealloc_size(int64_t total_size,
size_t cluster_size,
int refcount_order)
{
/* Note: The following calculation does not need to be exact; if it is a
* bit off, either some bytes will be "leaked" (which is fine) or we
* will need to increase the file size by some bytes (which is fine,
* too, as long as the bulk is allocated here). Therefore, using
* floating point arithmetic is fine. */
int64_t meta_size = 0;
uint64_t nreftablee, nrefblocke, nl1e, nl2e, refblock_count;
int64_t aligned_total_size = align_offset(total_size, cluster_size);
int cluster_bits = ctz32(cluster_size);
int refblock_bits, refblock_size;
/* refcount entry size in bytes */
double rces = (1 << refcount_order) / 8.;
/* see qcow2_open() */
refblock_bits = cluster_bits - (refcount_order - 3);
refblock_size = 1 << refblock_bits;
/* header: 1 cluster */
meta_size += cluster_size;
/* total size of L2 tables */
nl2e = aligned_total_size / cluster_size;
nl2e = align_offset(nl2e, cluster_size / sizeof(uint64_t));
meta_size += nl2e * sizeof(uint64_t);
/* total size of L1 tables */
nl1e = nl2e * sizeof(uint64_t) / cluster_size;
nl1e = align_offset(nl1e, cluster_size / sizeof(uint64_t));
meta_size += nl1e * sizeof(uint64_t);
/* total size of refcount blocks
*
* note: every host cluster is reference-counted, including metadata
* (even refcount blocks are recursively included).
* Let:
* a = total_size (this is the guest disk size)
* m = meta size not including refcount blocks and refcount tables
* c = cluster size
* y1 = number of refcount blocks entries
* y2 = meta size including everything
* rces = refcount entry size in bytes
* then,
* y1 = (y2 + a)/c
* y2 = y1 * rces + y1 * rces * sizeof(u64) / c + m
* we can get y1:
* y1 = (a + m) / (c - rces - rces * sizeof(u64) / c)
*/
nrefblocke = (aligned_total_size + meta_size + cluster_size)
/ (cluster_size - rces - rces * sizeof(uint64_t)
/ cluster_size);
refblock_count = DIV_ROUND_UP(nrefblocke, refblock_size);
meta_size += refblock_count * cluster_size;
/* total size of refcount tables */
nreftablee = align_offset(refblock_count,
cluster_size / sizeof(uint64_t));
meta_size += nreftablee * sizeof(uint64_t);
return meta_size + aligned_total_size;
}
static int qcow2_create2(const char *filename, int64_t total_size,
const char *backing_file, const char *backing_format,
int flags, size_t cluster_size, PreallocMode prealloc,
@ -2575,65 +2649,9 @@ static int qcow2_create2(const char *filename, int64_t total_size,
int ret;
if (prealloc == PREALLOC_MODE_FULL || prealloc == PREALLOC_MODE_FALLOC) {
/* Note: The following calculation does not need to be exact; if it is a
* bit off, either some bytes will be "leaked" (which is fine) or we
* will need to increase the file size by some bytes (which is fine,
* too, as long as the bulk is allocated here). Therefore, using
* floating point arithmetic is fine. */
int64_t meta_size = 0;
uint64_t nreftablee, nrefblocke, nl1e, nl2e, refblock_count;
int64_t aligned_total_size = align_offset(total_size, cluster_size);
int refblock_bits, refblock_size;
/* refcount entry size in bytes */
double rces = (1 << refcount_order) / 8.;
/* see qcow2_open() */
refblock_bits = cluster_bits - (refcount_order - 3);
refblock_size = 1 << refblock_bits;
/* header: 1 cluster */
meta_size += cluster_size;
/* total size of L2 tables */
nl2e = aligned_total_size / cluster_size;
nl2e = align_offset(nl2e, cluster_size / sizeof(uint64_t));
meta_size += nl2e * sizeof(uint64_t);
/* total size of L1 tables */
nl1e = nl2e * sizeof(uint64_t) / cluster_size;
nl1e = align_offset(nl1e, cluster_size / sizeof(uint64_t));
meta_size += nl1e * sizeof(uint64_t);
/* total size of refcount blocks
*
* note: every host cluster is reference-counted, including metadata
* (even refcount blocks are recursively included).
* Let:
* a = total_size (this is the guest disk size)
* m = meta size not including refcount blocks and refcount tables
* c = cluster size
* y1 = number of refcount blocks entries
* y2 = meta size including everything
* rces = refcount entry size in bytes
* then,
* y1 = (y2 + a)/c
* y2 = y1 * rces + y1 * rces * sizeof(u64) / c + m
* we can get y1:
* y1 = (a + m) / (c - rces - rces * sizeof(u64) / c)
*/
nrefblocke = (aligned_total_size + meta_size + cluster_size)
/ (cluster_size - rces - rces * sizeof(uint64_t)
/ cluster_size);
refblock_count = DIV_ROUND_UP(nrefblocke, refblock_size);
meta_size += refblock_count * cluster_size;
/* total size of refcount tables */
nreftablee = align_offset(refblock_count,
cluster_size / sizeof(uint64_t));
meta_size += nreftablee * sizeof(uint64_t);
qemu_opt_set_number(opts, BLOCK_OPT_SIZE,
aligned_total_size + meta_size, &error_abort);
int64_t prealloc_size =
qcow2_calc_prealloc_size(total_size, cluster_size, refcount_order);
qemu_opt_set_number(opts, BLOCK_OPT_SIZE, prealloc_size, &error_abort);
qemu_opt_set(opts, BLOCK_OPT_PREALLOC, PreallocMode_lookup[prealloc],
&error_abort);
}