block: perform zero-detection during copy-on-read
Copy-on-Read populates the image file with data read from a backing image. In order to avoid bloating the image file when all zeroes are read we should scan the buffer and perform an optimized zero write operation. Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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parent
f08f2ddae0
commit
79c053bde9
14
block.c
14
block.c
@ -1517,6 +1517,7 @@ static int coroutine_fn bdrv_co_do_copy_on_readv(BlockDriverState *bs,
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*/
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void *bounce_buffer;
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BlockDriver *drv = bs->drv;
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struct iovec iov;
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QEMUIOVector bounce_qiov;
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int64_t cluster_sector_num;
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@ -1537,14 +1538,21 @@ static int coroutine_fn bdrv_co_do_copy_on_readv(BlockDriverState *bs,
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iov.iov_base = bounce_buffer = qemu_blockalign(bs, iov.iov_len);
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qemu_iovec_init_external(&bounce_qiov, &iov, 1);
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ret = bs->drv->bdrv_co_readv(bs, cluster_sector_num, cluster_nb_sectors,
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&bounce_qiov);
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ret = drv->bdrv_co_readv(bs, cluster_sector_num, cluster_nb_sectors,
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&bounce_qiov);
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if (ret < 0) {
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goto err;
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}
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ret = bs->drv->bdrv_co_writev(bs, cluster_sector_num, cluster_nb_sectors,
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if (drv->bdrv_co_write_zeroes &&
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buffer_is_zero(bounce_buffer, iov.iov_len)) {
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ret = drv->bdrv_co_write_zeroes(bs, cluster_sector_num,
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cluster_nb_sectors);
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} else {
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ret = drv->bdrv_co_writev(bs, cluster_sector_num, cluster_nb_sectors,
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&bounce_qiov);
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}
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if (ret < 0) {
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/* It might be okay to ignore write errors for guest requests. If this
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* is a deliberate copy-on-read then we don't want to ignore the error.
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