Re: [Qemu-devel] [PATCH -V2] iohandler: update qemu_fd_set_handler to work with null call back arg

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

On Wed, 07 Sep 2011 13:44:39 -0500, Anthony Liguori <aliguori@us.ibm.com> wrote:
> On 09/07/2011 07:30 AM, Aneesh Kumar K.V wrote:
> > Many users of qemu_fd_set_handler including VirtFS use NULL call back arg.
> > Update fd_trampoline and qemu_fd_set_handler to work with NULL call back arg
> >
> > Signed-off-by: Aneesh Kumar K.V<aneesh.kumar@linux.vnet.ibm.com>
> > ---
> > Changes from V1:
> >     Add support for dropping event source
> >
> >   iohandler.c |   31 +++++++++++++------------------
> >   1 files changed, 13 insertions(+), 18 deletions(-)
> >
> > diff --git a/iohandler.c b/iohandler.c
> > index 5ef66fb..783f3ac 100644
> > --- a/iohandler.c
> > +++ b/iohandler.c
> > @@ -93,9 +93,8 @@ static gboolean fd_trampoline(GIOChannel *chan, GIOCondition cond, gpointer opaq
> >   {
> >       IOTrampoline *tramp = opaque;
> >
> > -    if (tramp->opaque == NULL) {
> > +    if (!tramp->fd_read&&  !tramp->fd_write)
> >           return FALSE;
> > -    }
> 
> Heh, this is pretty anti-CODING_STYLE :-)
> 
> At any rate, I think this whole segment has to go.  It's easier to not 
> deal with removing  sources in two places.
> 
> >
> >       if ((cond&  G_IO_IN)&&  tramp->fd_read) {
> >           tramp->fd_read(tramp->opaque);
> > @@ -113,6 +112,7 @@ int qemu_set_fd_handler(int fd,
> >                           IOHandler *fd_write,
> >                           void *opaque)
> >   {
> > +    GIOCondition cond = 0;
> >       static IOTrampoline fd_trampolines[FD_SETSIZE];
> >       IOTrampoline *tramp =&fd_trampolines[fd];
> >
> > @@ -121,25 +121,20 @@ int qemu_set_fd_handler(int fd,
> >           g_source_remove(tramp->tag);
> >       }
> >
> > -    if (opaque) {
> > -        GIOCondition cond = 0;
> > -
> > -        tramp->fd_read = fd_read;
> > -        tramp->fd_write = fd_write;
> > -        tramp->opaque = opaque;
> > -
> > -        if (fd_read) {
> > -            cond |= G_IO_IN | G_IO_ERR;
> > -        }
> > -
> > -        if (fd_write) {
> > -            cond |= G_IO_OUT | G_IO_ERR;
> > -        }
> > +    if (fd_read) {
> > +        cond |= G_IO_IN | G_IO_ERR;
> > +    }
> >
> > -        tramp->chan = g_io_channel_unix_new(fd);
> > -        tramp->tag = g_io_add_watch(tramp->chan, cond, fd_trampoline, tramp);
> > +    if (fd_write) {
> > +        cond |= G_IO_OUT | G_IO_ERR;
> >       }
> >
> > +    tramp->fd_read = fd_read;
> > +    tramp->fd_write = fd_write;
> > +    tramp->opaque = opaque;
> > +    tramp->chan = g_io_channel_unix_new(fd);
> > +    tramp->tag = g_io_add_watch(tramp->chan, cond, fd_trampoline, tramp);
> > +
> 
> I think this is a bit more complicated than is really needed.  Here's 
> what I came up with which also fixes another bug where the io channel 
> could be freed twice.  I stumbled across this via a very strange failure 
> scenario.  Avi, it might be worth trying this patch to see if it fixes 
> your problem too.
> 
> One thing that I found challenging debugging this, coroutines make 
> valgrind very unhappy.  Is it possible that we could have a command line 
> switch to fall back to the thread based coroutines so to make things 
> more valgrind friendly?

We definitely can look at a configure option that build with coroutine-gthread

> 
> diff --git a/iohandler.c b/iohandler.c
> index 5ef66fb..4cc1c5a 100644
> --- a/iohandler.c
> +++ b/iohandler.c
> @@ -93,10 +93,6 @@ static gboolean fd_trampoline(GIOChannel *chan, 
> GIOCondition cond, gpointer opaq
>   {
>       IOTrampoline *tramp = opaque;
> 
> -    if (tramp->opaque == NULL) {
> -        return FALSE;
> -    }
> -
>       if ((cond & G_IO_IN) && tramp->fd_read) {
>           tramp->fd_read(tramp->opaque);
>       }
> @@ -119,9 +115,10 @@ int qemu_set_fd_handler(int fd,
>       if (tramp->tag != 0) {
>           g_io_channel_unref(tramp->chan);
>           g_source_remove(tramp->tag);
> +        tramp->tag = 0;
>       }
> 
> -    if (opaque) {
> +    if (fd_read || fd_write || opaque) {
>           GIOCondition cond = 0;
> 
>           tramp->fd_read = fd_read;
> 

I tested above change with virtfs and it works.

-aneesh