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Date: Wed, 4 Mar 2015 14:01:33 +0100
From: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20150304130133.GM3465@noname.str.redhat.com>
References: <1425459851-16819-1-git-send-email-famz@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] block/null: Latency simulation by adding
 new option "latency_ns"
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To: Fam Zheng <famz@redhat.com>
Cc: qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>

Am 04.03.2015 um 10:04 hat Fam Zheng geschrieben:
> Aio context switch should just work because the requests will be
> drained, so the scheduled timer(s) on the old context will be freed.
> 
> Signed-off-by: Fam Zheng <famz@redhat.com>

You should probably also add co_aio_sleep_ns() calls to
null_co_readv/write/flush().

>  block/null.c | 34 ++++++++++++++++++++++++++++++++--
>  1 file changed, 32 insertions(+), 2 deletions(-)
> 
> diff --git a/block/null.c b/block/null.c
> index ec2bd27..af49525 100644
> --- a/block/null.c
> +++ b/block/null.c
> @@ -12,8 +12,11 @@
>  
>  #include "block/block_int.h"
>  
> +#define NULL_OPT_LATENCY "latency_ns"
> +
>  typedef struct {
>      int64_t length;
> +    int64_t latency_ns;
>  } BDRVNullState;
>  
>  static QemuOptsList runtime_opts = {
> @@ -30,6 +33,12 @@ static QemuOptsList runtime_opts = {
>              .type = QEMU_OPT_SIZE,
>              .help = "size of the null block",
>          },
> +        {
> +            .name = NULL_OPT_LATENCY,
> +            .type = QEMU_OPT_NUMBER,
> +            .help = "nanoseconds (approximated) to wait "
> +                    "before completing request",
> +        },
>          { /* end of list */ }
>      },
>  };
> @@ -44,6 +53,8 @@ static int null_file_open(BlockDriverState *bs, QDict *options, int flags,
>      qemu_opts_absorb_qdict(opts, options, &error_abort);
>      s->length =
>          qemu_opt_get_size(opts, BLOCK_OPT_SIZE, 1 << 30);
> +    s->latency_ns =
> +        qemu_opt_get_number(opts, NULL_OPT_LATENCY, 0);

s->latency_ns is signed, so I'd check for negative values.

The rest looks good to me.

Kevin