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


> -----Original Message-----
> From: Michael Kelley <mikelley@microsoft.com>
> Sent: Monday, December 30, 2019 8:35 PM
> To: Haiyang Zhang <haiyangz@microsoft.com>; sashal@kernel.org; linux-
> hyperv@vger.kernel.org; netdev@vger.kernel.org
> Cc: Haiyang Zhang <haiyangz@microsoft.com>; KY Srinivasan
> <kys@microsoft.com>; Stephen Hemminger <sthemmin@microsoft.com>;
> olaf@aepfle.de; vkuznets <vkuznets@redhat.com>; davem@davemloft.net;
> linux-kernel@vger.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@microsoft.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@microsoft.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

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