linux-kernel - Re: [PATCH next] xen: pcifront: Process failure for pcifront_(re)scan

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Date:	Tue, 14 Oct 2014 18:09:11 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Chen Gang <gang.chen.5i5j@...il.com>
Cc:	konrad.wilk@...cle.com, boris.ostrovsky@...cle.com,
	david.vrabel@...rix.com, xen-devel@...ts.xenproject.org,
	linux-pci@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH next] xen: pcifront: Process failure for
 pcifront_(re)scan_root()

On Mon, Oct 06, 2014 at 11:04:45AM +0800, Chen Gang wrote:
> When pcifront_rescan_root() or pcifront_scan_root() fails, need return
> error code, neither set XenbusStateConnected state, just like the other
> areas have done.
>
> For pcifront_rescan_root(), it will return error code ("num_roots = 0;",
> skip xenbus_switch_state return value).
> 
> For pcifront_scan_root(), it will return 0 ("num_roots = 0;", set 0 by
> the return value of xenbus_switch_state, which always return 0, at
> present).

The changelog is somewhat confusing because it talks about the patch hunks
in reverse order (the pcifront_scan_root() change is first in the patch,
but the changelog mentions pcifront_rescan_root() first).  I *think* this
means:

  When pcifront_try_connect() finds no PCI roots, it falls back to calling
  pcifront_scan_root() for 0000:00.  If that fails, it used to switch to
  XenbusStateConnected and return success (because xenbus_switch_state()
  currently always succeeds).

  If pcifront_scan_root() fails, leave the XenbusState unchanged and
  return an error code.

  Similarly, pcifront_attach_devices() falls back to calling
  pcifront_rescan_root() for 0000:00.  If that fails, it used to 
  switch to XenbusStateConnected and return an error code.

  If pcifront_rescan_root() fails, leave the XenbusState unchanged and
  return the error code.

The "num_roots" part doesn't seem relevant to me.

> Signed-off-by: Chen Gang <gang.chen.5i5j@...il.com>

Konrad, if you want to take this, feel free.  Otherwise, if you ack it and
you think my changelog understanding makes sense, I can pick it up.

It does seem odd that pcifront_attach_devices() ignores the
xenbus_switch_state() return value while pcifront_try_connect() does not.
But many other callers also ignore the return value, so maybe that's OK.

Bjorn

> ---
>  drivers/pci/xen-pcifront.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/pci/xen-pcifront.c b/drivers/pci/xen-pcifront.c
> index 53df39a..d78d884 100644
> --- a/drivers/pci/xen-pcifront.c
> +++ b/drivers/pci/xen-pcifront.c
> @@ -866,6 +866,11 @@ static int pcifront_try_connect(struct pcifront_device *pdev)
>  		xenbus_dev_error(pdev->xdev, err,
>  				 "No PCI Roots found, trying 0000:00");
>  		err = pcifront_scan_root(pdev, 0, 0);
> +		if (err) {
> +			xenbus_dev_fatal(pdev->xdev, err,
> +					 "Error scanning PCI root 0000:00");
> +			goto out;
> +		}
>  		num_roots = 0;
>  	} else if (err != 1) {
>  		if (err == 0)
> @@ -947,6 +952,11 @@ static int pcifront_attach_devices(struct pcifront_device *pdev)
>  		xenbus_dev_error(pdev->xdev, err,
>  				 "No PCI Roots found, trying 0000:00");
>  		err = pcifront_rescan_root(pdev, 0, 0);
> +		if (err) {
> +			xenbus_dev_fatal(pdev->xdev, err,
> +					 "Error scanning PCI root 0000:00");
> +			goto out;
> +		}
>  		num_roots = 0;
>  	} else if (err != 1) {
>  		if (err == 0)
> -- 
> 1.9.3
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