netdev - RE: [PATCH V2,net-next, 1/3] Drivers: hv: vmbus: Add a dev_num variable based on channel offer sequence

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Date:   Tue, 31 Dec 2019 15:48:49 +0000
From:   Haiyang Zhang <haiyangz@...rosoft.com>
To:     Michael Kelley <mikelley@...rosoft.com>,
        "sashal@...nel.org" <sashal@...nel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     KY Srinivasan <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "olaf@...fle.de" <olaf@...fle.de>, vkuznets <vkuznets@...hat.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH V2,net-next, 1/3] Drivers: hv: vmbus: Add a dev_num
 variable based on channel offer sequence



> -----Original Message-----
> From: Michael Kelley <mikelley@...rosoft.com>
> Sent: Monday, December 30, 2019 8:35 PM
> To: Haiyang Zhang <haiyangz@...rosoft.com>; sashal@...nel.org; linux-
> hyperv@...r.kernel.org; netdev@...r.kernel.org
> Cc: Haiyang Zhang <haiyangz@...rosoft.com>; KY Srinivasan
> <kys@...rosoft.com>; Stephen Hemminger <sthemmin@...rosoft.com>;
> olaf@...fle.de; vkuznets <vkuznets@...hat.com>; davem@...emloft.net;
> linux-kernel@...r.kernel.org
> Subject: RE: [PATCH V2,net-next, 1/3] Drivers: hv: vmbus: Add a dev_num
> variable based on channel offer sequence
> 
> From: Haiyang Zhang <haiyangz@...rosoft.com> Sent: Monday, December 30,
> 2019 12:14 PM
> >
> > This number is set to the first available number, starting from zero,
> > when a vmbus device's primary channel is offered.
> 
> Let's use "VMBus" as the capitalization in text.
Sure I will.

> 
> > It will be used for stable naming when Async probing is used.
> >
> > Signed-off-by: Haiyang Zhang <haiyangz@...rosoft.com>
> > ---
> > Changes
> > V2:
> > 	Use nest loops in hv_set_devnum, instead of goto.
> >
> >  drivers/hv/channel_mgmt.c | 38
> ++++++++++++++++++++++++++++++++++++--
> >  include/linux/hyperv.h    |  6 ++++++
> >  2 files changed, 42 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
> > index 8eb1675..00fa2db 100644
> > --- a/drivers/hv/channel_mgmt.c
> > +++ b/drivers/hv/channel_mgmt.c
> > @@ -315,6 +315,8 @@ static struct vmbus_channel *alloc_channel(void)
> >  	if (!channel)
> >  		return NULL;
> >
> > +	channel->dev_num = HV_DEV_NUM_INVALID;
> > +
> >  	spin_lock_init(&channel->lock);
> >  	init_completion(&channel->rescind_event);
> >
> > @@ -541,6 +543,36 @@ static void vmbus_add_channel_work(struct
> work_struct *work)
> >  }
> >
> >  /*
> > + * Get the first available device number of its type, then
> > + * record it in the channel structure.
> > + */
> > +static void hv_set_devnum(struct vmbus_channel *newchannel)
> > +{
> > +	struct vmbus_channel *channel;
> > +	int i = -1;
> > +	bool found;
> > +
> > +	BUG_ON(!mutex_is_locked(&vmbus_connection.channel_mutex));
> > +
> > +	do {
> > +		i++;
> > +		found = false;
> > +
> > +		list_for_each_entry(channel, &vmbus_connection.chn_list,
> > +				    listentry) {
> > +			if (i == channel->dev_num &&
> > +			    guid_equal(&channel->offermsg.offer.if_type,
> > +				       &newchannel->offermsg.offer.if_type)) {
> > +				found = true;
> > +				break;
> > +			}
> > +		}
> > +	} while (found);
> > +
> > +	newchannel->dev_num = i;
> > +}
> > +
> 
> It took me a little while to figure out what the above algorithm is doing.
> Perhaps it would help to rename the "found" variable to "in_use", and add
> this comment before the start of the "do" loop:
> 
> Iterate through each possible device number starting at zero.  If the device
> number is already in use for a device of this type, try the next device number
> until finding one that is not in use.   This approach selects the smallest
> device number that is not in use, and so reuses any numbers that are freed
> by devices that have been removed.
I will rename the variable, and add the code comments.
Thanks,

- Haiyang