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Date:   Fri, 20 Jul 2018 09:04:15 -0400 (EDT)
From:   Pankaj Gupta <pagupta@redhat.com>
To:     Luiz Capitulino <lcapitulino@redhat.com>
Cc:     Stefan Hajnoczi <stefanha@redhat.com>, kwolf@redhat.com,
        haozhong zhang <haozhong.zhang@intel.com>, jack@suse.cz,
        xiaoguangrong eric <xiaoguangrong.eric@gmail.com>,
        kvm@vger.kernel.org, riel@surriel.com, linux-nvdimm@ml01.01.org,
        david@redhat.com, ross zwisler <ross.zwisler@intel.com>,
        linux-kernel@vger.kernel.org, qemu-devel@nongnu.org,
        hch@infradead.org, imammedo@redhat.com, mst@redhat.com,
        niteshnarayanlal@hotmail.com, pbonzini@redhat.com,
        dan j williams <dan.j.williams@intel.com>, nilal@redhat.com
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References: <20180713075232.9575-1-pagupta@redhat.com> <20180713075232.9575-4-pagupta@redhat.com> <20180718085529.133a0a22@doriath> <367397176.52317488.1531979293251.JavaMail.zimbra@redhat.com> <20180719121635.GA28107@stefanha-x1.localdomain> <20180719084819.730b7971@doriath>
Subject: Re: [Qemu-devel] [RFC v3] qemu: Add virtio pmem device
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Thread-Topic: qemu: Add virtio pmem device
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> > > > > +
> > > > > +typedef struct VirtIOPMEMresp {
> > > > > +    int ret;
> > > > > +} VirtIOPMEMResp;
> > > > > +
> > > > > +typedef struct VirtIODeviceRequest {
> > > > > +    VirtQueueElement elem;
> > > > > +    int fd;
> > > > > +    VirtIOPMEM *pmem;
> > > > > +    VirtIOPMEMResp resp;
> > > > > +} VirtIODeviceRequest;
> > > > > +
> > > > > +static int worker_cb(void *opaque)
> > > > > +{
> > > > > +    VirtIODeviceRequest *req = opaque;
> > > > > +    int err = 0;
> > > > > +
> > > > > +    /* flush raw backing image */
> > > > > +    err = fsync(req->fd);
> > > > > +    if (err != 0) {
> > > > > +        err = errno;
> > > > > +    }
> > > > > +    req->resp.ret = err;
> > > > 
> > > > Host question: are you returning the guest errno code to the host?
> > > 
> > > No. I am returning error code from the host in-case of host fsync
> > > failure, otherwise returning zero.
> > 
> > I think that's what Luiz meant.  errno constants are not portable
> > between operating systems and architectures.  Therefore they cannot be
> > used in external interfaces in software that expects to communicate with
> > other systems.
> 
> Oh, thanks. Only saw this email now.
> 
> > It will be necessary to define specific constants for virtio-pmem
> > instead of passing errno from the host to guest.
> 
> Yes, defining your own constants work. But I think the only fsync()
> error that will make sense for the guest is EIO. The other errors
> only make sense for the host.

Agree.

Thanks,
Pankaj