netdev - RE: [PATCHv3 5/7] tap: Extending tap device create/destroy APIs

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Date:   Thu, 2 Feb 2017 23:22:48 +0000
From:   "Grandhi, Sainath" <sainath.grandhi@...el.com>
To:     David Miller <davem@...emloft.net>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "mahesh@...dewar.net" <mahesh@...dewar.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCHv3 5/7] tap: Extending tap device create/destroy APIs



> -----Original Message-----
> From: David Miller [mailto:davem@...emloft.net]
> Sent: Tuesday, January 31, 2017 9:51 AM
> To: Grandhi, Sainath <sainath.grandhi@...el.com>
> Cc: netdev@...r.kernel.org; mahesh@...dewar.net; linux-
> kernel@...r.kernel.org
> Subject: Re: [PATCHv3 5/7] tap: Extending tap device create/destroy APIs
> 
> From: Sainath Grandhi <sainath.grandhi@...el.com>
> Date: Mon, 30 Jan 2017 11:12:00 -0800
> 
> > +	list_for_each_entry_safe(tap_major, tmp, &major_list, next) {
> > +		if (tap_major->major == major) {
> > +			return tap_major;
> > +		}
> > +	}
> 
> Single line basic blocks, such as this 'if' statement, should not be surrounded
> by curly braces.
> 
> Also I see not mutual exclusion being implemented to protect this list.  If there
> is, it is not obvious, so it should be documented with a comment explaining
> what protects the list.
Ok. It's my fault to not include safe reading of the list.
I would use the RCU API for list traversal, adding and deleting entries.
Please look for it in my next version.

> 
> > @@ -1175,14 +1228,7 @@ int tap_create_cdev(struct cdev *tap_cdev,
> >  	if (err)
> >  		goto out2;
> >
> > -	macvtap_major.major = MAJOR(*tap_major);
> > -
> > -	idr_init(&macvtap_major.minor_idr);
> > -	mutex_init(&macvtap_major.minor_lock);
> > -
> > -	macvtap_major.device_name = device_name;
> > -
> > -	return err;
> > +	return tap_list_add(*tap_major, device_name);
> >
> >  out2:
> >  	unregister_chrdev_region(*tap_major, TAP_NUM_DEVS);
> 
> If tap_list_add() fails, you will leave the chrdev region registered.
Thanks. Would take care of it.