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Date: Fri, 18 Apr 2008 15:29:10 +0900
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From: gnn@freebsd.org
To: vijay singh <vijjus@rocketmail.com>
In-Reply-To: <490341.95478.qm@web33501.mail.mud.yahoo.com>
References: <490341.95478.qm@web33501.mail.mud.yahoo.com>
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Cc: freebsd-net@freebsd.org
Subject: Re: Regarding if_alloc()
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At Thu, 17 Apr 2008 18:35:23 -0700 (PDT),
vijay singh wrote:
> 
> Hi all. How do we avoid a race in populating the ifindex_table? Id
> this is a TODO, as it seems from the code below, would it be
> acceptable if I wrote a patch and reused the ifnet_lock
> [IFNET_WLOCK, IFNET_WUNLOCK]?
> 

It is almost always acceptable to submit a patch :-)

> 
> if_alloc(u_char type)
> {
>     struct ifnet *ifp;
> 
>     ifp = malloc(sizeof(struct ifnet), M_IFNET, M_WAITOK|M_ZERO);
> 
>     /*
>      * Try to find an empty slot below if_index.  If we fail, take
>      * the next slot.
>      *
>      * XXX: should be locked!
>      */
>     for (ifp->if_index = 1; ifp->if_index <= if_index; ifp->if_index++) {
>         if (ifnet_byindex(ifp->if_index) == NULL)
>             break;
>     }
> 
> 

There are still parts of the network device infrastructure that need
some locking, and it would seem that this is one of them.  I know
Brooks Davis was also looking at this stuff so he may comment as well.

Best,
George