jcs.org
qemu with hax to log dma reads & writes
jcs.org/2018/11/12/vfio
qcow2: Support BDRV_REQ_ZERO_WRITE for truncate
If BDRV_REQ_ZERO_WRITE is set and we're extending the image, calling
qcow2_cluster_zeroize() with flags=0 does the right thing: It doesn't
undo any previous preallocation, but just adds the zero flag to all
relevant L2 entries. If an external data file is in use, a write_zeroes
request to the data file is made instead.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20200424125448.63318-5-kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
+35
-1
+1
-1
block/qcow2-cluster.c
+1
-1
block/qcow2-cluster.c
···
1795
1795
/* Caller must pass aligned values, except at image end */
1796
1796
assert(QEMU_IS_ALIGNED(offset, s->cluster_size));
1797
1797
assert(QEMU_IS_ALIGNED(end_offset, s->cluster_size) ||
1798
-
end_offset == bs->total_sectors << BDRV_SECTOR_BITS);
1798
+
end_offset >= bs->total_sectors << BDRV_SECTOR_BITS);
1799
1799
1800
1800
/* The zero flag is only supported by version 3 and newer */
1801
1801
if (s->qcow_version < 3) {
+34
block/qcow2.c
+34
block/qcow2.c
···
1726
1726
1727
1727
bs->supported_zero_flags = header.version >= 3 ?
1728
1728
BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK : 0;
1729
+
bs->supported_truncate_flags = BDRV_REQ_ZERO_WRITE;
1729
1730
1730
1731
/* Repair image if dirty */
1731
1732
if (!(flags & (BDRV_O_CHECK | BDRV_O_INACTIVE)) && !bs->read_only &&
···
4212
4213
4213
4214
default:
4214
4215
g_assert_not_reached();
4216
+
}
4217
+
4218
+
if ((flags & BDRV_REQ_ZERO_WRITE) && offset > old_length) {
4219
+
uint64_t zero_start = QEMU_ALIGN_UP(old_length, s->cluster_size);
4220
+
4221
+
/*
4222
+
* Use zero clusters as much as we can. qcow2_cluster_zeroize()
4223
+
* requires a cluster-aligned start. The end may be unaligned if it is
4224
+
* at the end of the image (which it is here).
4225
+
*/
4226
+
ret = qcow2_cluster_zeroize(bs, zero_start, offset - zero_start, 0);
4227
+
if (ret < 0) {
4228
+
error_setg_errno(errp, -ret, "Failed to zero out new clusters");
4229
+
goto fail;
4230
+
}
4231
+
4232
+
/* Write explicit zeros for the unaligned head */
4233
+
if (zero_start > old_length) {
4234
+
uint64_t len = zero_start - old_length;
4235
+
uint8_t *buf = qemu_blockalign0(bs, len);
4236
+
QEMUIOVector qiov;
4237
+
qemu_iovec_init_buf(&qiov, buf, len);
4238
+
4239
+
qemu_co_mutex_unlock(&s->lock);
4240
+
ret = qcow2_co_pwritev_part(bs, old_length, len, &qiov, 0, 0);
4241
+
qemu_co_mutex_lock(&s->lock);
4242
+
4243
+
qemu_vfree(buf);
4244
+
if (ret < 0) {
4245
+
error_setg_errno(errp, -ret, "Failed to zero out the new area");
4246
+
goto fail;
4247
+
}
4248
+
}
4215
4249
}
4216
4250
4217
4251
if (prealloc != PREALLOC_MODE_OFF) {