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Re: [Qemu-devel] [PATCH 1/1] block: fix inability to start VM with nativ
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH 1/1] block: fix inability to start VM with native AIO |
Date: |
Wed, 23 Dec 2015 16:07:01 +0800 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
On Tue, Dec 22, 2015 at 09:59:46AM +0300, Denis V. Lunev wrote:
> error: Failed to start domain rhel7
> error: internal error: process exited while connecting to monitor:
> 2015-12-22T06:55:18.812637Z qemu-system-x86_64:
> -drive file=/var/lib/libvirt/images/rhel7.qcow2,if=none,
> id=drive-scsi0-0-0-0,format=qcow2,cache=none,aio=native:
> aio=native was specified, but it requires cache.direct=on,
> which was not specified.
>
> cache=none option was specified as seen above while the VM is unable to
> start. The patch properly passed BDRV_O_NOCACHE to underlying layer.
>
> The problem is revealed with
> commit d657c0c289e944fc22289f5c318f48da87d79dcb
> Author: Kevin Wolf <address@hidden>
> Date: Tue Dec 15 11:35:36 2015 +0100
>
> raw-posix: Make aio=native option binding
>
> Signed-off-by: Denis V. Lunev <address@hidden>
> CC: Kevin Wolf <address@hidden>
> ---
> block.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/block.c b/block.c
> index 411edbf..fe0fbbc 100644
> --- a/block.c
> +++ b/block.c
> @@ -990,6 +990,7 @@ static int bdrv_open_common(BlockDriverState *bs,
> BdrvChild *file,
> bs->opaque = g_malloc0(drv->instance_size);
>
> /* Apply cache mode options */
> + update_flags_from_options(&open_flags, opts);
> update_flags_from_options(&bs->open_flags, opts);
> bdrv_set_enable_write_cache(bs, bs->open_flags & BDRV_O_CACHE_WB);
I tried to review this patch and failed to understand block.c flags
handling. Perhaps there is a larger problem here because I see:
1. .bdrv_open() and friends take an int flags argument in addition to
the already open bs node, which has bs->open_flags. Some of the code
that manipulates the flags argument in block.c updates bs->open_flags
to keep them in sync. Some code does not (e.g. BDRV_O_NO_BACKING).
Is this a bug?
Should int flags be removed in favor of just bs->open_flags?
2. The bdrv_open_common() open_flags local variable contains different
values from bs->open_flags (i.e. BDRV_O_PROTOCOL). I'm not sure
whether this is intentional or a bug.
Your patch syncs them but I wonder if it would be cleaner to remove
the open_flags local (avoiding similar problems in the future)?
3. block/qcow2.c stashes .bdrv_open(flags) in s->flags. I'm not sure
if bs->open_flags can be used instead of s->flags. That would be
simpler.
Maybe someone can explain how this is all supposed to work.
Stefan
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