From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stefan Hajnoczi <stefanha@gmail.com>
Subject: Re: [RFC v2] qemu: Add virtio pmem device
Date: Thu, 26 Apr 2018 14:24:06 +0100
Message-ID: <20180426132406.GC30991@stefanha-x1.localdomain>
References: <20180425112415.12327-1-pagupta@redhat.com>
 <20180425112415.12327-4-pagupta@redhat.com>
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To: Pankaj Gupta <pagupta@redhat.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, qemu-devel@nongnu.org, linux-nvdimm@ml01.01.org, linux-mm@kvack.org, jack@suse.cz, stefanha@redhat.com, dan.j.williams@intel.com, riel@surriel.com, haozhong.zhang@intel.com, nilal@redhat.com, kwolf@redhat.com, pbonzini@redhat.com, ross.zwisler@intel.com, david@redhat.com, xiaoguangrong.eric@gmail.com, hch@infradead.org, marcel@redhat.com, mst@redhat.com, niteshnarayanlal@hotmail.com, imammedo@redhat.com, lcapitulino@redhat.com
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On Wed, Apr 25, 2018 at 04:54:15PM +0530, Pankaj Gupta wrote:
> +static void virtio_pmem_flush(VirtIODevice *vdev, VirtQueue *vq)
> +{
> +    VirtQueueElement *elem;
> +    VirtIOPMEM *pmem = VIRTIO_PMEM(vdev);
> +    HostMemoryBackend *backend = MEMORY_BACKEND(pmem->memdev);
> +    int fd = memory_region_get_fd(&backend->mr);
> +
> +    elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
> +    if (!elem) {
> +        return;
> +    }
> +    /* flush raw backing image */
> +    fsync(fd);

fsync(2) is a blocking syscall.  This can hang QEMU for an unbounded
amount of time.

Please do the fsync from a thread pool.  See block/file-posix.c's
aio_worker() for an example.

> +static void virtio_pmem_get_config(VirtIODevice *vdev, uint8_t *config)
> +{
> +    VirtIOPMEM *pmem = VIRTIO_PMEM(vdev);
> +    struct virtio_pmem_config *pmemcfg = (struct virtio_pmem_config *) config;
> +
> +    pmemcfg->start = pmem->start;
> +    pmemcfg->size  = pmem->size;

Endianness.  Please use virtio_st*_p() instead.

> +#define VIRTIO_PMEM_PLUG 0

What is this?

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