MFC r206637:

When an underlying ioctl(2) handler returns an error, our ioctl(2)
interface considers that it hits a fatal error, and will not copyout
the request structure back for _IOW and _IOWR ioctls, keeping them
untouched.

The previous implementation of the SIOCGIFDESCR ioctl intends to
feed the buffer length back to userland.  However, if we return
an error, the feedback would be defeated and ifconfig(8) would
trap into an infinite loop.

This commit changes SIOCGIFDESCR to set buffer field to NULL to
indicate the previous ENAMETOOLONG case.

Reported by:	bschmidt

1 files changed, 6 insertions, 3 deletions

diff --git a/share/man/man4/netintro.4 b/share/man/man4/netintro.4
index 348a13e..3e98940 100644
--- a/share/man/man4/netintro.4
+++ b/share/man/man4/netintro.4
@@ -32,7 +32,7 @@
 .\"     @(#)netintro.4	8.2 (Berkeley) 11/30/93
 .\" $FreeBSD$
 .\"
-.Dd January 26, 2010
+.Dd April 14, 2010
 .Dt NETINTRO 4
 .Os
 .Sh NAME
@@ -292,8 +292,11 @@ field of
 struct passed in as parameter, and the length would include
 the terminating nul character.
 If there is not enough space to hold the interface length,
-no copy would be done and an
-error would be returned.
+no copy would be done and the
+.Va buffer
+field of
+.Va ifru_buffer
+would be set to NULL.
 The kernel will store the buffer length in the
 .Va length
 field upon return, regardless whether the buffer itself is