Re: [PATCH] virtio-pci: add softlinks between virtio and pci

From: Anthony Liguori
Date: Wed Jan 05 2011 - 15:06:46 EST


On 01/05/2011 01:38 PM, Michael S. Tsirkin wrote:
On Wed, Jan 05, 2011 at 01:28:34PM -0600, Anthony Liguori wrote:
On 01/05/2011 01:17 PM, Michael S. Tsirkin wrote:
We sometimes need to map between the virtio device and
the given pci device. One such use is OS installer that
gets the boot pci device from BIOS and needs to
find the relevant block device. Since it can't,
installation fails.
I have no objection to this patch but I'm a tad confused by the description.

I assume you mean the installer is querying the boot device via
int13 get driver parameters such that it returns the pci address of
the device?

Or is it querying geometry information and then trying to find the
best match block device?
I think it's the former.

If it's the former, I don't really understand the need for a
backlink since the PCI address gives you a link to the block device.
It does? How does it?

Okay, after some more discussion, I think I better understand what's going on here.

The installer needs to figure out the boot device. It does this by querying the BIOS and the BIOS can only give it back a PCI address. Right now, if you follow the PCI sysfs path, you cannot reach the actual virtio device because the PCI device only refers to the bus. This is because virtio has a separate struct device than the PCI struct device. These explicit links establish the relationship.

A lot of this would be cleaner if virtio didn't force an independent struct device and could simply make use of an already existing struct device.

Regards,

Anthony Liguori

OTOH, if it's the later, it would make sense but then your
description doesn't really make much sense.

At any rate, a better commit message would be helpful in explaining
the need for this.

Regards,

Anthony Liguori

Supply softlinks between these to make it possible.

Signed-off-by: Michael S. Tsirkin<mst@xxxxxxxxxx>
---

Gleb, could you please ack that this patch below
will be enough to fix the installer issue that
you see?

drivers/virtio/virtio_pci.c | 18 +++++++++++++++++-
1 files changed, 17 insertions(+), 1 deletions(-)

diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
index ef8d9d5..06eb2f8 100644
--- a/drivers/virtio/virtio_pci.c
+++ b/drivers/virtio/virtio_pci.c
@@ -25,6 +25,7 @@
#include<linux/virtio_pci.h>
#include<linux/highmem.h>
#include<linux/spinlock.h>
+#include<linux/sysfs.h>

MODULE_AUTHOR("Anthony Liguori<aliguori@xxxxxxxxxx>");
MODULE_DESCRIPTION("virtio-pci");
@@ -667,8 +668,21 @@ static int __devinit virtio_pci_probe(struct pci_dev *pci_dev,
if (err)
goto out_set_drvdata;

- return 0;
+ err = sysfs_create_link(&pci_dev->dev.kobj,&vp_dev->vdev.dev.kobj,
+ "virtio_device");
+ if (err)
+ goto out_register_device;
+
+ err = sysfs_create_link(&vp_dev->vdev.dev.kobj,&pci_dev->dev.kobj,
+ "bus_device");
+ if (err)
+ goto out_create_link;

+ return 0;
+out_create_link:
+ sysfs_remove_link(&pci_dev->dev.kobj, "virtio_device");
+out_register_device:
+ unregister_virtio_device(&vp_dev->vdev);
out_set_drvdata:
pci_set_drvdata(pci_dev, NULL);
pci_iounmap(pci_dev, vp_dev->ioaddr);
@@ -685,6 +699,8 @@ static void __devexit virtio_pci_remove(struct pci_dev *pci_dev)
{
struct virtio_pci_device *vp_dev = pci_get_drvdata(pci_dev);

+ sysfs_remove_link(&vp_dev->vdev.dev.kobj, "bus_device");
+ sysfs_remove_link(&pci_dev->dev.kobj, "virtio_device");
unregister_virtio_device(&vp_dev->vdev);
}


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