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Re: [PATCH 3/5] block/nbd.c: Add yank feature
From: |
Daniel P . Berrangé |
Subject: |
Re: [PATCH 3/5] block/nbd.c: Add yank feature |
Date: |
Fri, 15 May 2020 11:26:13 +0100 |
User-agent: |
Mutt/1.13.4 (2020-02-15) |
On Fri, May 15, 2020 at 12:14:47PM +0200, Lukas Straub wrote:
> On Fri, 15 May 2020 11:04:13 +0100
> Daniel P. Berrangé <address@hidden> wrote:
>
> > On Fri, May 15, 2020 at 11:48:18AM +0200, Lukas Straub wrote:
> > > On Tue, 12 May 2020 09:54:58 +0100
> > > Daniel P. Berrangé <address@hidden> wrote:
> > >
> > > > On Mon, May 11, 2020 at 07:05:24PM +0200, Lukas Straub wrote:
> > > > > On Mon, 11 May 2020 17:19:09 +0100
> > > > > "Dr. David Alan Gilbert" <address@hidden> wrote:
> > > > >
> > > > > > * Lukas Straub (address@hidden) wrote:
> > > > > > > Add yank option, pass it to the socket-channel and register a yank
> > > > > > > function which sets s->state = NBD_CLIENT_QUIT. This is the same
> > > > > > > behaviour as if an error occured.
> > > > > > >
> > > > > > > Signed-off-by: Lukas Straub <address@hidden>
> > > > > >
> > > > > > > +static void nbd_yank(void *opaque)
> > > > > > > +{
> > > > > > > + BlockDriverState *bs = opaque;
> > > > > > > + BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
> > > > > > > +
> > > > > > > + atomic_set(&s->state, NBD_CLIENT_QUIT);
> > > > > >
> > > > > > I think I was expecting a shutdown on the socket here - why doesn't
> > > > > > it
> > > > > > have one?
> > > > >
> > > > > For nbd, we register two yank functions: This one and we enable
> > > > > the yank feature on the qio channel (see function
> > > > > nbd_establish_connection below).
> > > >
> > > > As mentioned on the earlier patch, I don't want to see any yank
> > > > code in the QIOChannel object directly. This nbd_yank function
> > > > can simply call the qio_channel_shutdown() function directly
> > > > and avoid need for modifying the QIOChannel object with yank
> > > > support.
> > >
> > > Hi,
> > > Looking at it again, the problem is not with registering the yank
> > > functions, but with tracking the lifetime of it. Suppose we add
> > > qio_channel_shutdown to the yank_nbd function. Then we need to unregister
> > > it whenever the QIOChannel object is freed.
> > >
> > > In the code that would lead to the following constructs in a lot of
> > > places:
> > > if (local_err) {
> > > yank_unregister_function(s->yank_name, yank_nbd, bs);
> > > object_unref(OBJECT(sioc));
> > > error_propagate(errp, local_err);
> > > return NULL;
> > > }
> >
> > The nbd patch here already has a yank_unregister_function() so I'm
> > not seeing anything changes in that respect. The "yank_nbd" function
> > should check that the I/O channel is non-NULL before calling the
> > qio_channel_shutdown method.
>
> Hmm, but if object_unref frees the object, it doesn't set the
> pointer to NULL does it?
So set "ioc = NULL" after calling object_unref. AFAICT, nbd already
does exactly this.
Regards,
Daniel
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- Re: [PATCH 2/5] io/channel.c,io/channel-socket.c: Add yank feature, (continued)
[PATCH 3/5] block/nbd.c: Add yank feature, Lukas Straub, 2020/05/11
- Re: [PATCH 3/5] block/nbd.c: Add yank feature, Dr. David Alan Gilbert, 2020/05/11
- Re: [PATCH 3/5] block/nbd.c: Add yank feature, Lukas Straub, 2020/05/11
- Re: [PATCH 3/5] block/nbd.c: Add yank feature, Dr. David Alan Gilbert, 2020/05/11
- Re: [PATCH 3/5] block/nbd.c: Add yank feature, Daniel P . Berrangé, 2020/05/12
- Re: [PATCH 3/5] block/nbd.c: Add yank feature, Lukas Straub, 2020/05/15
- Re: [PATCH 3/5] block/nbd.c: Add yank feature, Daniel P . Berrangé, 2020/05/15
- Re: [PATCH 3/5] block/nbd.c: Add yank feature, Lukas Straub, 2020/05/15
- Re: [PATCH 3/5] block/nbd.c: Add yank feature,
Daniel P . Berrangé <=
- Re: [PATCH 3/5] block/nbd.c: Add yank feature, Lukas Straub, 2020/05/15
- Re: [PATCH 3/5] block/nbd.c: Add yank feature, Daniel P . Berrangé, 2020/05/15
[PATCH 4/5] chardev/char-socket.c: Add yank feature, Lukas Straub, 2020/05/11
[PATCH 5/5] migration: Add yank feature, Lukas Straub, 2020/05/11
Re: [PATCH 0/5] Introduce 'yank' oob qmp command to recover from hanging qemu, Daniel P . Berrangé, 2020/05/11