Re: Unable to talk to tap(4)
On Thu, 15 May 2008 14:49:26 -0400
Bob McConnell [EMAIL PROTECTED] wrote:
My code so far:
- tear along dotted line -
tapFD = open (/dev/tap0, O_RDWR);
if (tapFD 0) {
fprintf (stderr, Failed to open /dev/tap0: %d.\n, tapFD);
exit (2);
}
fprintf (stderr, Successfully opened /dev/tap0.\n);
unsigned char * buffer = (unsigned char*)malloc(1514);
if (buffer = NULL) {
if (buffer == NULL) {
fprintf (stderr, No memory available.\n);
close (tapFD);
exit(3);
}
When I replace the malloc with an automatic array, the
error goes away and I get the data I am looking for. i.e.:
unsigned char buffer[1514];
So why can't I use malloc to create that buffer?
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Re: Unable to talk to tap(4)
unsigned char * buffer = (unsigned char*)malloc(1514);
is stdlib.h included (i'm asking for sure)?
if (buffer = NULL) {
if (buffer == NULL) {
fprintf (stderr, No memory available.\n);
close (tapFD);
exit(3);
}
When I replace the malloc with an automatic array, the
error goes away and I get the data I am looking for. i.e.:
unsigned char buffer[1514];
So why can't I use malloc to create that buffer?
anyway not using malloc is good habit :) but it should work anyway.
try
buffer[0]=buffer[1513]=0;
to make sure page is actually allocated.
if this help - maybe tap driver is buggy.
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Re: Unable to talk to tap(4)
Bob McConnell [EMAIL PROTECTED] writes:
From: Bob McConnell
From: Wojciech Puchar
The basic setup sequence is:
ifconfig tap0 create
ifconfig tap0 inet 10.3.4.254/24
route -v add 10.3.4.0/24 10.3.4.254
ifconfig tap0 up
?
'ifconfig' already showed the interface flag UP. Adding this command
to the sequence has no effect on it. I also tried 'ifconfig tap0
promisc'.
Is EFAULT really a memory access exception?
At this point, I can ping that address and my application can open
either /dev/net/tap0 or /dev/tap0. But when I try to read() from
those
devices, I have problems.
/dev/net/tap0 always returns with errno = 19 (ENODEV - Operation not
supported?).
/dev/tap0 returns errno = 14 (EFAULT - bad address). At this point,
'ifconfig' shows that the inet address is no longer attached and
'netstat -rn' shows the route I added above has been dropped.
I have been searching for several days to find more information
about
this device, but have not found anything specific to FreeBSD. All of
the
examples and instructions are for Linux or tun(4), both of which are
significantly different devices.
My code so far:
- tear along dotted line -
tapFD = open (/dev/tap0, O_RDWR);
if (tapFD 0) {
fprintf (stderr, Failed to open /dev/tap0: %d.\n, tapFD);
exit (2);
}
fprintf (stderr, Successfully opened /dev/tap0.\n);
unsigned char * buffer = (unsigned char*)malloc(1514);
if (buffer = NULL) {
fprintf (stderr, No memory available.\n);
close (tapFD);
exit(3);
}
When I replace the malloc with an automatic array, the
error goes away and I get the data I am looking for. i.e.:
unsigned char buffer[1514];
So why can't I use malloc to create that buffer?
Maybe you forgot to include stdlib.h? That could end up with the
compiler adjusting the parameters incorrectly.
Incidentally, this problem is why casting the return value of malloc
is discouraged; the compiler would warn about such a problem if the
(completely unnecessary) cast were not present.
int lenth = 0;
again:
lenth = read(tapFD, buffer, 1514);
if (lenth 0) {
int error = errno;
if (error == EINTR)
goto again;
fprintf (stderr, tap read error: %d\n, error);
}
else {
int index;
fprintf (stdout, %d bytes received.\n, lenth);
for (index = 0; index lenth; ++index) {
fprintf (stdout, %02x, buffer[index]);
if (index % 16 == 15)
fprintf (stdout, \n);
}
fprintf (stdout, \n);
}
close (tapFD);
- tear along dotted line -
Just in the interest of full disclosure, I am running a stock
installation of FreeBSD 7.0 in a VMWare 5.5.4 session on WinXP.
There
are also two virtual Ethernet cards, one connected to a host only
subnet, the other bridged onto a real Ethernet segment. I am using
IPFW
with DummyNet to inject some measure of reality into this system.
This is the beginnings of a test bench for several commercial
applications. My goal, once I get this device working, is to write
an
application for tap(4) that will emulate a few hundred embedded
devices,
each opening a socket directly to a server, which currently resides
in
another VM session on the host only network. This setup, coupled
with
real devices on the external network should give us a much more
realistic environment for stress testing our systems.
Thank you,
Bob McConnell
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--
Lowell Gilbert, embedded/networking software engineer, Boston area
http://be-well.ilk.org/~lowell/
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RE: Unable to talk to tap(4)
From: Wojciech Puchar
if (buffer = NULL) {
if (buffer == NULL) {
anyway not using malloc is good habit :) but it should work anyway.
try
The test after the malloc was the problem. I have been working in a
poorly designed scripting language for several months where the single
'=' is used for comparisons and didn't see the difference when I got
back into C. Setting a pointer to NULL should always cause an EFAULT.
Unfortunately, even 'gcc -Wall' didn't generate an appropriate warning
for it.
I only use malloc when I won't know how many buffers I need until run
time. In this case the application will count records in a configuration
file and malloc (1514 * count * 2) bytes, where count can range from 1
to 2000. That becomes an array of buffers, so I can pass just an index
or pointer between threads, usually through a mailbox or message queue.
It's a simple trick for message passing that I picked up years ago while
using the CTASK and XINU kernels.
Thanks for all the help,
Bob McConnell
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RE: Unable to talk to tap(4)
On Fri, 16 May 2008, Bob McConnell wrote:
From: Wojciech Puchar
if (buffer = NULL) {
if (buffer == NULL) {
anyway not using malloc is good habit :) but it should work anyway.
try
The test after the malloc was the problem. I have been working in a
:)
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RE: Unable to talk to tap(4)
From: Wojciech Puchar
The basic setup sequence is:
ifconfig tap0 create
ifconfig tap0 inet 10.3.4.254/24
route -v add 10.3.4.0/24 10.3.4.254
ifconfig tap0 up
?
'ifconfig' already showed the interface flag UP. Adding this command
to the sequence has no effect on it. I also tried 'ifconfig tap0
promisc'.
Is EFAULT really a memory access exception?
At this point, I can ping that address and my application can open
either /dev/net/tap0 or /dev/tap0. But when I try to read() from
those
devices, I have problems.
/dev/net/tap0 always returns with errno = 19 (ENODEV - Operation not
supported?).
/dev/tap0 returns errno = 14 (EFAULT - bad address). At this point,
'ifconfig' shows that the inet address is no longer attached and
'netstat -rn' shows the route I added above has been dropped.
I have been searching for several days to find more information about
this device, but have not found anything specific to FreeBSD. All of
the
examples and instructions are for Linux or tun(4), both of which are
significantly different devices.
My code so far:
- tear along dotted line -
tapFD = open (/dev/tap0, O_RDWR);
if (tapFD 0) {
fprintf (stderr, Failed to open /dev/tap0: %d.\n, tapFD);
exit (2);
}
fprintf (stderr, Successfully opened /dev/tap0.\n);
unsigned char * buffer = (unsigned char*)malloc(1514);
if (buffer = NULL) {
fprintf (stderr, No memory available.\n);
close (tapFD);
exit(3);
}
int lenth = 0;
again:
lenth = read(tapFD, buffer, 1514);
if (lenth 0) {
int error = errno;
if (error == EINTR)
goto again;
fprintf (stderr, tap read error: %d\n, error);
}
else {
int index;
fprintf (stdout, %d bytes received.\n, lenth);
for (index = 0; index lenth; ++index) {
fprintf (stdout, %02x, buffer[index]);
if (index % 16 == 15)
fprintf (stdout, \n);
}
fprintf (stdout, \n);
}
close (tapFD);
- tear along dotted line -
Just in the interest of full disclosure, I am running a stock
installation of FreeBSD 7.0 in a VMWare 5.5.4 session on WinXP. There
are also two virtual Ethernet cards, one connected to a host only
subnet, the other bridged onto a real Ethernet segment. I am using
IPFW
with DummyNet to inject some measure of reality into this system.
This is the beginnings of a test bench for several commercial
applications. My goal, once I get this device working, is to write an
application for tap(4) that will emulate a few hundred embedded
devices,
each opening a socket directly to a server, which currently resides
in
another VM session on the host only network. This setup, coupled with
real devices on the external network should give us a much more
realistic environment for stress testing our systems.
Thank you,
Bob McConnell
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RE: Unable to talk to tap(4)
From: Bob McConnell
From: Wojciech Puchar
The basic setup sequence is:
ifconfig tap0 create
ifconfig tap0 inet 10.3.4.254/24
route -v add 10.3.4.0/24 10.3.4.254
ifconfig tap0 up
?
'ifconfig' already showed the interface flag UP. Adding this command
to the sequence has no effect on it. I also tried 'ifconfig tap0
promisc'.
Is EFAULT really a memory access exception?
At this point, I can ping that address and my application can open
either /dev/net/tap0 or /dev/tap0. But when I try to read() from
those
devices, I have problems.
/dev/net/tap0 always returns with errno = 19 (ENODEV - Operation not
supported?).
/dev/tap0 returns errno = 14 (EFAULT - bad address). At this point,
'ifconfig' shows that the inet address is no longer attached and
'netstat -rn' shows the route I added above has been dropped.
I have been searching for several days to find more information
about
this device, but have not found anything specific to FreeBSD. All of
the
examples and instructions are for Linux or tun(4), both of which are
significantly different devices.
My code so far:
- tear along dotted line -
tapFD = open (/dev/tap0, O_RDWR);
if (tapFD 0) {
fprintf (stderr, Failed to open /dev/tap0: %d.\n, tapFD);
exit (2);
}
fprintf (stderr, Successfully opened /dev/tap0.\n);
unsigned char * buffer = (unsigned char*)malloc(1514);
if (buffer = NULL) {
fprintf (stderr, No memory available.\n);
close (tapFD);
exit(3);
}
When I replace the malloc with an automatic array, the
error goes away and I get the data I am looking for. i.e.:
unsigned char buffer[1514];
So why can't I use malloc to create that buffer?
int lenth = 0;
again:
lenth = read(tapFD, buffer, 1514);
if (lenth 0) {
int error = errno;
if (error == EINTR)
goto again;
fprintf (stderr, tap read error: %d\n, error);
}
else {
int index;
fprintf (stdout, %d bytes received.\n, lenth);
for (index = 0; index lenth; ++index) {
fprintf (stdout, %02x, buffer[index]);
if (index % 16 == 15)
fprintf (stdout, \n);
}
fprintf (stdout, \n);
}
close (tapFD);
- tear along dotted line -
Just in the interest of full disclosure, I am running a stock
installation of FreeBSD 7.0 in a VMWare 5.5.4 session on WinXP.
There
are also two virtual Ethernet cards, one connected to a host only
subnet, the other bridged onto a real Ethernet segment. I am using
IPFW
with DummyNet to inject some measure of reality into this system.
This is the beginnings of a test bench for several commercial
applications. My goal, once I get this device working, is to write
an
application for tap(4) that will emulate a few hundred embedded
devices,
each opening a socket directly to a server, which currently resides
in
another VM session on the host only network. This setup, coupled
with
real devices on the external network should give us a much more
realistic environment for stress testing our systems.
Thank you,
Bob McConnell
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Unable to talk to tap(4)
Good morning,
Does anyone here have experience using tap(4)? I am trying to do some
basic I/O with it, but am not having any success. I have gotten to the
point where I can create and configure the device, and my application
can open it, but read() always returns errors.
The basic setup sequence is:
ifconfig tap0 create
ifconfig tap0 inet 10.3.4.254/24
route -v add 10.3.4.0/24 10.3.4.254
At this point, I can ping that address and my application can open
either /dev/net/tap0 or /dev/tap0. But when I try to read() from those
devices, I have problems.
/dev/net/tap0 always returns with errno = 19 (ENODEV - Operation not
supported?).
/dev/tap0 returns errno = 14 (EFAULT - bad address). At this point,
'ifconfig' shows that the inet address is no longer attached and
'netstat -rn' shows the route I added above has been dropped.
I have been searching for several days to find more information about
this device, but have not found anything specific to FreeBSD. All of the
examples and instructions are for Linux or tun(4), both of which are
significantly different devices.
My code so far:
- tear along dotted line -
tapFD = open (/dev/tap0, O_RDWR);
if (tapFD 0) {
fprintf (stderr, Failed to open /dev/tap0: %d.\n, tapFD);
exit (2);
}
fprintf (stderr, Successfully opened /dev/tap0.\n);
unsigned char * buffer = (unsigned char*)malloc(1514);
if (buffer = NULL) {
fprintf (stderr, No memory available.\n);
close (tapFD);
exit(3);
}
int lenth = 0;
again:
lenth = read(tapFD, buffer, 1514);
if (lenth 0) {
int error = errno;
if (error == EINTR)
goto again;
fprintf (stderr, tap read error: %d\n, error);
}
else {
int index;
fprintf (stdout, %d bytes received.\n, lenth);
for (index = 0; index lenth; ++index) {
fprintf (stdout, %02x, buffer[index]);
if (index % 16 == 15)
fprintf (stdout, \n);
}
fprintf (stdout, \n);
}
close (tapFD);
- tear along dotted line -
Just in the interest of full disclosure, I am running a stock
installation of FreeBSD 7.0 in a VMWare 5.5.4 session on WinXP. There
are also two virtual Ethernet cards, one connected to a host only
subnet, the other bridged onto a real Ethernet segment. I am using IPFW
with DummyNet to inject some measure of reality into this system.
This is the beginnings of a test bench for several commercial
applications. My goal, once I get this device working, is to write an
application for tap(4) that will emulate a few hundred embedded devices,
each opening a socket directly to a server, which currently resides in
another VM session on the host only network. This setup, coupled with
real devices on the external network should give us a much more
realistic environment for stress testing our systems.
Thank you,
Bob McConnell
Principal Communications Programmer
The CBORD Group, Inc.
61 Brown Road
Ithaca NY, 14850
Phone 607 257-2410
FAX 607 257-1902
Email [EMAIL PROTECTED]
Web www.cbord.com
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Re: Unable to talk to tap(4)
The basic setup sequence is:
ifconfig tap0 create
ifconfig tap0 inet 10.3.4.254/24
route -v add 10.3.4.0/24 10.3.4.254
ifconfig tap0 up
?
At this point, I can ping that address and my application can open
either /dev/net/tap0 or /dev/tap0. But when I try to read() from those
devices, I have problems.
/dev/net/tap0 always returns with errno = 19 (ENODEV - Operation not
supported?).
/dev/tap0 returns errno = 14 (EFAULT - bad address). At this point,
'ifconfig' shows that the inet address is no longer attached and
'netstat -rn' shows the route I added above has been dropped.
I have been searching for several days to find more information about
this device, but have not found anything specific to FreeBSD. All of the
examples and instructions are for Linux or tun(4), both of which are
significantly different devices.
My code so far:
- tear along dotted line -
tapFD = open (/dev/tap0, O_RDWR);
if (tapFD 0) {
fprintf (stderr, Failed to open /dev/tap0: %d.\n, tapFD);
exit (2);
}
fprintf (stderr, Successfully opened /dev/tap0.\n);
unsigned char * buffer = (unsigned char*)malloc(1514);
if (buffer = NULL) {
fprintf (stderr, No memory available.\n);
close (tapFD);
exit(3);
}
int lenth = 0;
again:
lenth = read(tapFD, buffer, 1514);
if (lenth 0) {
int error = errno;
if (error == EINTR)
goto again;
fprintf (stderr, tap read error: %d\n, error);
}
else {
int index;
fprintf (stdout, %d bytes received.\n, lenth);
for (index = 0; index lenth; ++index) {
fprintf (stdout, %02x, buffer[index]);
if (index % 16 == 15)
fprintf (stdout, \n);
}
fprintf (stdout, \n);
}
close (tapFD);
- tear along dotted line -
Just in the interest of full disclosure, I am running a stock
installation of FreeBSD 7.0 in a VMWare 5.5.4 session on WinXP. There
are also two virtual Ethernet cards, one connected to a host only
subnet, the other bridged onto a real Ethernet segment. I am using IPFW
with DummyNet to inject some measure of reality into this system.
This is the beginnings of a test bench for several commercial
applications. My goal, once I get this device working, is to write an
application for tap(4) that will emulate a few hundred embedded devices,
each opening a socket directly to a server, which currently resides in
another VM session on the host only network. This setup, coupled with
real devices on the external network should give us a much more
realistic environment for stress testing our systems.
Thank you,
Bob McConnell
Principal Communications Programmer
The CBORD Group, Inc.
61 Brown Road
Ithaca NY, 14850
Phone 607 257-2410
FAX 607 257-1902
Email [EMAIL PROTECTED]
Web www.cbord.com
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