Re: [Xen-devel] [PATCH v3 2/3] xen/pciback: avoid multiple entries in slot list

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 09/22/2016 04:45 AM, Juergen Gross wrote:
> The Xen pciback driver has a list of all pci devices it is ready to
> seize. There is no check whether a to be added entry already exists.
> While this might be no problem in the common case it might confuse
> those which consume the list via sysfs.
>
> Modify the handling of this list by not adding an entry which already
> exists. As this will be needed later split out the list handling into
> a separate function.
>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
>  drivers/xen/xen-pciback/pci_stub.c | 39 
> ++++++++++++++++++++++++++++++--------
>  1 file changed, 31 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/xen/xen-pciback/pci_stub.c 
> b/drivers/xen/xen-pciback/pci_stub.c
> index 79a9e4d..0179333 100644
> --- a/drivers/xen/xen-pciback/pci_stub.c
> +++ b/drivers/xen/xen-pciback/pci_stub.c
> @@ -478,6 +478,36 @@ static int __init pcistub_init_devices_late(void)
>       return 0;
>  }
>  
> +static void pcistub_device_id_add_list(struct pcistub_device_id *new,
> +                                    int domain, int bus, unsigned int devfn)
> +{
> +     struct pcistub_device_id *pci_dev_id;
> +     unsigned long flags;
> +     int found = 0;
> +
> +     spin_lock_irqsave(&device_ids_lock, flags);
> +
> +     list_for_each_entry(pci_dev_id, &pcistub_device_ids, slot_list) {
> +             if (pci_dev_id->domain == domain && pci_dev_id->bus == bus &&
> +                 pci_dev_id->devfn == devfn) {
> +                     found = 1;
> +                     break;
> +             }
> +     }
> +
> +     if (!found) {
> +             new->domain = domain;
> +             new->bus = bus;
> +             new->devfn = devfn;
> +             list_add_tail(&new->slot_list, &pcistub_device_ids);
> +     }
> +
> +     spin_unlock_irqrestore(&device_ids_lock, flags);
> +
> +     if (found)
> +             kfree(new);

I'd rather free 'new' in the caller (who allocated it) and return
something like -EEXIST if device is already on the list.

-boris

> +}
> +
>  static int pcistub_seize(struct pci_dev *dev)
>  {
>       struct pcistub_device *psdev;
> @@ -1012,7 +1042,6 @@ static inline int str_to_quirk(const char *buf, int 
> *domain, int *bus, int
>  static int pcistub_device_id_add(int domain, int bus, int slot, int func)
>  {
>       struct pcistub_device_id *pci_dev_id;
> -     unsigned long flags;
>       int rc = 0, devfn = PCI_DEVFN(slot, func);
>  
>       if (slot < 0) {
> @@ -1042,16 +1071,10 @@ static int pcistub_device_id_add(int domain, int bus, 
> int slot, int func)
>       if (!pci_dev_id)
>               return -ENOMEM;
>  
> -     pci_dev_id->domain = domain;
> -     pci_dev_id->bus = bus;
> -     pci_dev_id->devfn = devfn;
> -
>       pr_debug("wants to seize %04x:%02x:%02x.%d\n",
>                domain, bus, slot, func);
>  
> -     spin_lock_irqsave(&device_ids_lock, flags);
> -     list_add_tail(&pci_dev_id->slot_list, &pcistub_device_ids);
> -     spin_unlock_irqrestore(&device_ids_lock, flags);
> +     pcistub_device_id_add_list(pci_dev_id, domain, bus, devfn);
>  
>       return 0;
>  }


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