netdev - Re: [PATCH] netdevice.7: document SIOCGIFCONF case ifc

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Date:	Thu, 16 Jan 2014 17:23:58 +1300
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Tilman Schmidt <tilman@...p.cc>
CC:	mtk.manpages@...il.com, linux-man@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH] netdevice.7: document SIOCGIFCONF case ifc_req==NULL

On 01/11/2014 08:35 AM, Tilman Schmidt wrote:
> Hello Michael,
> 
> Am 10.01.2014 18:52, schrieb Michael Kerrisk (man-pages):
>> On 01/10/2014 12:30 PM, Tilman Schmidt wrote:
>>> Add the missing description of the possibility to call SIOCGIFCONF
>>> with ifc_req==NULL to determine the needed buffer size, as described
>>> in http://lkml.indiana.edu/hypermail/linux/kernel/0110.1/0506.html
>>> and verified against source files net/core/dev_ioctl.c and
>>> net/ipv4/devinet.c in the current kernel git tree.
> [...]>
>> Thanks for the patch. I'm trying to verify this from the code, but 
>> am having some trouble finding the relevant pieces. Could you point
>> me more specifically at the points in the kernel source where this
>> case is handled?
> 
> Gladly.
> 
> Function dev_ifconf() [net/core/dev_ioctl.c line 67ff.] is the main
> handler for SIOCGIFCONF. It calls the registered protocol specific
> handlers via the table gifconf_list[]. The current kernel has only
> one such handler, inet_gifconf() [net/ipv4/devinet.c line 1115ff.]
> 
> If ifc.ifc_buf is NULL, dev_ifconf() calls the protocol specific
> handlers with NULL as second argument. [net/core/dev_ioctl.c line 96]
> 
> If inet_gifconf() is called with NULL as second argument it just
> adds up the data sizes, skipping the size check and data transfer.
> [net/ipv4/devinet.c line 1127f.]

Thanks. Patch applied.

Cheers,

Michael




-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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