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

Dr. David Alan Gilbert
2018-12-13T10:00:59Z

* David Hildenbrand (david@redhat.com) wrote:
> On 13.12.18 10:13, Dr. David Alan Gilbert wrote:
> > * David Hildenbrand (david@redhat.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@redhat.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?

No, these need cleaning up; and the split within the bar
is probably going to change to be communicated via virtio layer
rather than pci capabilities. However, I don't want to make our PCI
device look odd, just to make portability to non-PCI devices - so it's
right to make the split appropriately, but still to use PCI bars
for what they were designed for.

Dave

>
> --
>
> Thanks,
>
> David / dhildenb
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK