block/null-{co,aio}: Allow reading zeroes
This is optional so that it does not impede the null block driver's performance unless this behavior is desired. Signed-off-by: Max Reitz <mreitz@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Acked-by: Fam Zheng <famz@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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block/null.c
20
block/null.c
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@ -15,10 +15,12 @@
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#include "block/block_int.h"
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#define NULL_OPT_LATENCY "latency-ns"
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#define NULL_OPT_ZEROES "read-zeroes"
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typedef struct {
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int64_t length;
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int64_t latency_ns;
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bool read_zeroes;
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} BDRVNullState;
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static QemuOptsList runtime_opts = {
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@ -41,6 +43,11 @@ static QemuOptsList runtime_opts = {
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.help = "nanoseconds (approximated) to wait "
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"before completing request",
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},
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{
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.name = NULL_OPT_ZEROES,
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.type = QEMU_OPT_BOOL,
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.help = "return zeroes when read",
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},
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{ /* end of list */ }
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},
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};
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@ -62,6 +69,7 @@ static int null_file_open(BlockDriverState *bs, QDict *options, int flags,
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error_setg(errp, "latency-ns is invalid");
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ret = -EINVAL;
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}
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s->read_zeroes = qemu_opt_get_bool(opts, NULL_OPT_ZEROES, false);
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qemu_opts_del(opts);
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return ret;
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}
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@ -91,6 +99,12 @@ static coroutine_fn int null_co_readv(BlockDriverState *bs,
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int64_t sector_num, int nb_sectors,
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QEMUIOVector *qiov)
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{
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BDRVNullState *s = bs->opaque;
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if (s->read_zeroes) {
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qemu_iovec_memset(qiov, 0, 0, nb_sectors * BDRV_SECTOR_SIZE);
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}
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return null_co_common(bs);
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}
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@ -160,6 +174,12 @@ static BlockAIOCB *null_aio_readv(BlockDriverState *bs,
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BlockCompletionFunc *cb,
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void *opaque)
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{
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BDRVNullState *s = bs->opaque;
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if (s->read_zeroes) {
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qemu_iovec_memset(qiov, 0, 0, nb_sectors * BDRV_SECTOR_SIZE);
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}
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return null_aio_common(bs, cb, opaque);
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}
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