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

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Message-ID: <a2b62ca2-d0a9-b8d1-63c0-f4a039c9b7da@suse.com>
Date:   Fri, 23 Sep 2016 06:02:26 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org
Cc:     david.vrabel@...rix.com
Subject: Re: [PATCH v3 2/3] xen/pciback: avoid multiple entries in slot list

On 22/09/16 23:02, Boris Ostrovsky wrote:
> 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@...e.com>
>> ---
>>  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.

Hmm, I thought of this, but with two callers after the following patch
having to deal with the situation I've chosen this way to do it.

The code is smaller this way.


Juergen