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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>
This commit is contained in:
Max Reitz 2016-03-24 23:33:58 +01:00 committed by Kevin Wolf
parent aad15de427
commit cd219eb1e5
1 changed files with 20 additions and 0 deletions
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20
block/null.c
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@ -15,10 +15,12 @@
#include "block/block_int.h"
#define NULL_OPT_LATENCY "latency-ns"
#define NULL_OPT_ZEROES "read-zeroes"
typedef struct {
int64_t length;
int64_t latency_ns;
bool read_zeroes;
} BDRVNullState;
static QemuOptsList runtime_opts = {
@ -41,6 +43,11 @@ static QemuOptsList runtime_opts = {
.help = "nanoseconds (approximated) to wait "
"before completing request",
},
{
.name = NULL_OPT_ZEROES,
.type = QEMU_OPT_BOOL,
.help = "return zeroes when read",
},
{ /* end of list */ }
},
};
@ -62,6 +69,7 @@ static int null_file_open(BlockDriverState *bs, QDict *options, int flags,
error_setg(errp, "latency-ns is invalid");
ret = -EINVAL;
}
s->read_zeroes = qemu_opt_get_bool(opts, NULL_OPT_ZEROES, false);
qemu_opts_del(opts);
return ret;
}
@ -91,6 +99,12 @@ static coroutine_fn int null_co_readv(BlockDriverState *bs,
int64_t sector_num, int nb_sectors,
QEMUIOVector *qiov)
{
BDRVNullState *s = bs->opaque;
if (s->read_zeroes) {
qemu_iovec_memset(qiov, 0, 0, nb_sectors * BDRV_SECTOR_SIZE);
}
return null_co_common(bs);
}
@ -160,6 +174,12 @@ static BlockAIOCB *null_aio_readv(BlockDriverState *bs,
BlockCompletionFunc *cb,
void *opaque)
{
BDRVNullState *s = bs->opaque;
if (s->read_zeroes) {
qemu_iovec_memset(qiov, 0, 0, nb_sectors * BDRV_SECTOR_SIZE);
}
return null_aio_common(bs, cb, opaque);
}