linux-kernel - Re: [PATCH 18/52] virtio-fs: Map cache using the values from the capabilities

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Date:   Thu, 13 Dec 2018 10:34:57 +0100
From:   David Hildenbrand <david@...hat.com>
To:     "Dr. David Alan Gilbert" <dgilbert@...hat.com>
Cc:     Vivek Goyal <vgoyal@...hat.com>, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        miklos@...redi.hu, stefanha@...hat.com, sweil@...hat.com,
        swhiteho@...hat.com
Subject: Re: [PATCH 18/52] virtio-fs: Map cache using the values from the
 capabilities

On 13.12.18 10:13, Dr. David Alan Gilbert wrote:
> * David Hildenbrand (david@...hat.com) wrote:
>> On 10.12.18 18:12, Vivek Goyal wrote:
>>> Instead of assuming we had the fixed bar for the cache, use the
>>> value from the capabilities.
>>>
>>> Signed-off-by: Dr. David Alan Gilbert <dgilbert@...hat.com>
>>> ---
>>>  fs/fuse/virtio_fs.c | 32 +++++++++++++++++---------------
>>>  1 file changed, 17 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
>>> index 60d496c16841..55bac1465536 100644
>>> --- a/fs/fuse/virtio_fs.c
>>> +++ b/fs/fuse/virtio_fs.c
>>> @@ -14,11 +14,6 @@
>>>  #include <uapi/linux/virtio_pci.h>
>>>  #include "fuse_i.h"
>>>  
>>> -enum {
>>> -	/* PCI BAR number of the virtio-fs DAX window */
>>> -	VIRTIO_FS_WINDOW_BAR = 2,
>>> -};
>>> -
>>>  /* List of virtio-fs device instances and a lock for the list */
>>>  static DEFINE_MUTEX(virtio_fs_mutex);
>>>  static LIST_HEAD(virtio_fs_instances);
>>> @@ -518,7 +513,7 @@ static int virtio_fs_setup_dax(struct virtio_device *vdev, struct virtio_fs *fs)
>>>  	struct dev_pagemap *pgmap;
>>>  	struct pci_dev *pci_dev;
>>>  	phys_addr_t phys_addr;
>>> -	size_t len;
>>> +	size_t bar_len;
>>>  	int ret;
>>>  	u8 have_cache, cache_bar;
>>>  	u64 cache_offset, cache_len;
>>> @@ -551,17 +546,13 @@ static int virtio_fs_setup_dax(struct virtio_device *vdev, struct virtio_fs *fs)
>>>          }
>>>  
>>>  	/* TODO handle case where device doesn't expose BAR? */
>>
>> For virtio-pmem we decided to not go via BARs as this would effectively
>> make it only usable for virtio-pci implementers. Instead, we are going
>> to export the applicable physical device region directly (e.g.
>> phys_start, phys_size in virtio config), so it is decoupled from PCI
>> details. Doing the same for virtio-fs would allow e.g. also virtio-ccw
>> to make eventually use of this.
> 
> That makes it a very odd looking PCI device;  I can see that with
> virtio-pmem it makes some sense, given that it's job is to expose
> arbitrary chunks of memory.
> 
> Dave

Well, the fact that your are

- including <uapi/linux/virtio_pci.h>
- adding pci related code

in/to fs/fuse/virtio_fs.c

tells me that these properties might be better communicated on the
virtio layer, not on the PCI layer.

Or do you really want to glue virtio-fs to virtio-pci for all eternity?


-- 

Thanks,

David / dhildenb