xinit hangs on XWin infinite loop when using -displayfd

xinit hangs on XWin infinite loop when using -displayfd

[Matt D.]

The operating system is Windows XP Professional. It is a CLEAN install 
on a VMware virtual machine and is 100% patched up. Cygwin also is a 
clean install. I did try a rebaseall with no effect.

This is the first time I've encountered this. When I run "xinit -- 
-displayfd 3", xinit will hang and XWin takes up 100% of the cpu.

I've confirmed that file descriptors are working:

$ exec 3>a
$ echo "test" >&3
$ cat a
test
$ exec 3>&-

I can confirm that ports are available and that both xinit and XWin work 
without this argument by running:

$ xinit --

Everything else works fine but without "-displayfd" I can't record where 
the display is for this session to disk.

I've also tried copying known-working Cygwin installs into the VM and 
still have the same error. Copying the erroring install from the VM 
outside and running it on my development machine (Windows 7 x64) does 
not generate an error.

Unless something stands out here, I can provide the VMware image for 
testing (how convenient).


Matt D.

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Re: xinit hangs on XWin infinite loop when using -displayfd

[Matt D.]

Still hangs with the latest 1.15.1-4 release.

On my main machine, I get the following output:

$ xinit -- -displayfd 1

read display number ':0' from X server
0

On the VM it just hangs. Taskmanager shows xinit.exe waiting or hung 
with XWin.exe churning cycles and eating memory; about 4kB a tick.

Also on the VM, if I run the following:

$ xinit -- -displayfd

Then the display will open. So it seems to be an issue with whatever 
code is dealing with the file descriptors.


Matt D.

On 7/20/2014 9:06 PM, Matt D. wrote:
> The operating system is Windows XP Professional. It is a CLEAN install
> on a VMware virtual machine and is 100% patched up. Cygwin also is a
> clean install. I did try a rebaseall with no effect.
>
> This is the first time I've encountered this. When I run "xinit --
> -displayfd 3", xinit will hang and XWin takes up 100% of the cpu.
>
> I've confirmed that file descriptors are working:
>
> $ exec 3>a
> $ echo "test" >&3
> $ cat a
> test
> $ exec 3>&-
>
> I can confirm that ports are available and that both xinit and XWin work
> without this argument by running:
>
> $ xinit --
>
> Everything else works fine but without "-displayfd" I can't record where
> the display is for this session to disk.
>
> I've also tried copying known-working Cygwin installs into the VM and
> still have the same error. Copying the erroring install from the VM
> outside and running it on my development machine (Windows 7 x64) does
> not generate an error.
>
> Unless something stands out here, I can provide the VMware image for
> testing (how convenient).
>
>
> Matt D.
>
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Re: xinit hangs on XWin infinite loop when using -displayfd

[Matt D.]

Ok.. so I let xinit do its thing to see if it got anywhere. Eventually 
it will pop and error box. Interestingly, I specified a displayfd value 
of "3" and yet both the popup and the log are reporting "5":

http://oi58.tinypic.com/106fono.jpg

My XWin.0.log is about 15MB of repeated attempts to open a socket. Here 
is a snippet. I hope this helps:

InitConnectionLimits: MaxClients = 255
Welcome to the XWin X Server
Vendor: The Cygwin/X Project
Release: 1.15.1.0
OS: CYGWIN_NT-5.1 matthew-17ffb52 1.7.30(0.272/5/3) 2014-05-23 10:36 i686
OS: Windows XP Service Pack 3 [Windows NT 5.1 build 2600] (Win32)
Snapshot: 20140709-git-2e9c13ea41c51df7

XWin was started with the following command line:

X -displayfd 5

ddxProcessArgument - Initializing default screens
winInitializeScreenDefaults - primary monitor w 1062 h 703
winInitializeScreenDefaults - native DPI x 96 y 96
ddxProcessArgument - arg: -displayfd
Trying to create socket for display number 0
_XSERVTransSocketOpenCOTSServer: Unable to open socket for inet6
_XSERVTransOpen: transport open failed for inet6/matthew-17ffb52:0
_XSERVTransMakeAllCOTSServerListeners: failed to open listener for inet6

..


Trying to create socket for display number 59534
_XSERVTransSocketOpenCOTSServer: Unable to open socket for inet6
_XSERVTransOpen: transport open failed for inet6/matthew-17ffb52:59534
_XSERVTransMakeAllCOTSServerListeners: failed to open listener for inet6
(EE) Fatal server error:
(EE) Failed to find a socket to listen on(EE)
[ 58128.390] (EE) Server terminated with error (1). Closing log file.


Matt D.

On 7/21/2014 11:49 AM, Matt D. wrote:
> Still hangs with the latest 1.15.1-4 release.
>
> On my main machine, I get the following output:
>
> $ xinit -- -displayfd 1
>
> read display number ':0' from X server
> 0
>
> On the VM it just hangs. Taskmanager shows xinit.exe waiting or hung
> with XWin.exe churning cycles and eating memory; about 4kB a tick.
>
> Also on the VM, if I run the following:
>
> $ xinit -- -displayfd
>
> Then the display will open. So it seems to be an issue with whatever
> code is dealing with the file descriptors.
>
>
> Matt D.
>
> On 7/20/2014 9:06 PM, Matt D. wrote:
>> The operating system is Windows XP Professional. It is a CLEAN install
>> on a VMware virtual machine and is 100% patched up. Cygwin also is a
>> clean install. I did try a rebaseall with no effect.
>>
>> This is the first time I've encountered this. When I run "xinit --
>> -displayfd 3", xinit will hang and XWin takes up 100% of the cpu.
>>
>> I've confirmed that file descriptors are working:
>>
>> $ exec 3>a
>> $ echo "test" >&3
>> $ cat a
>> test
>> $ exec 3>&-
>>
>> I can confirm that ports are available and that both xinit and XWin work
>> without this argument by running:
>>
>> $ xinit --
>>
>> Everything else works fine but without "-displayfd" I can't record where
>> the display is for this session to disk.
>>
>> I've also tried copying known-working Cygwin installs into the VM and
>> still have the same error. Copying the erroring install from the VM
>> outside and running it on my development machine (Windows 7 x64) does
>> not generate an error.
>>
>> Unless something stands out here, I can provide the VMware image for
>> testing (how convenient).
>>
>>
>> Matt D.
>>
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>>
>>
>>
>
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>
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Re: xinit hangs on XWin infinite loop when using -displayfd

[Matt D.]

I found as a workaround to add the arguments "-nolisten tcp" when 
invoking xinit. However, I was under the impression that it was 
incompatible with -multiwindow and -clipboard, both of which seem to be 
working fine:

https://cygwin.com/ml/cygwin-xfree/2009-05/msg00016.html


Matt D.

On 7/21/2014 12:00 PM, Matt D. wrote:
> Ok.. so I let xinit do its thing to see if it got anywhere. Eventually
> it will pop and error box. Interestingly, I specified a displayfd value
> of "3" and yet both the popup and the log are reporting "5":
>
> http://oi58.tinypic.com/106fono.jpg
>
> My XWin.0.log is about 15MB of repeated attempts to open a socket. Here
> is a snippet. I hope this helps:
>
> InitConnectionLimits: MaxClients = 255
> Welcome to the XWin X Server
> Vendor: The Cygwin/X Project
> Release: 1.15.1.0
> OS: CYGWIN_NT-5.1 matthew-17ffb52 1.7.30(0.272/5/3) 2014-05-23 10:36 i686
> OS: Windows XP Service Pack 3 [Windows NT 5.1 build 2600] (Win32)
> Snapshot: 20140709-git-2e9c13ea41c51df7
>
> XWin was started with the following command line:
>
> X -displayfd 5
>
> ddxProcessArgument - Initializing default screens
> winInitializeScreenDefaults - primary monitor w 1062 h 703
> winInitializeScreenDefaults - native DPI x 96 y 96
> ddxProcessArgument - arg: -displayfd
> Trying to create socket for display number 0
> _XSERVTransSocketOpenCOTSServer: Unable to open socket for inet6
> _XSERVTransOpen: transport open failed for inet6/matthew-17ffb52:0
> _XSERVTransMakeAllCOTSServerListeners: failed to open listener for inet6
>
> ..
>
>
> Trying to create socket for display number 59534
> _XSERVTransSocketOpenCOTSServer: Unable to open socket for inet6
> _XSERVTransOpen: transport open failed for inet6/matthew-17ffb52:59534
> _XSERVTransMakeAllCOTSServerListeners: failed to open listener for inet6
> (EE) Fatal server error:
> (EE) Failed to find a socket to listen on(EE)
> [ 58128.390] (EE) Server terminated with error (1). Closing log file.
>
>
> Matt D.
>
> On 7/21/2014 11:49 AM, Matt D. wrote:
>> Still hangs with the latest 1.15.1-4 release.
>>
>> On my main machine, I get the following output:
>>
>> $ xinit -- -displayfd 1
>>
>> read display number ':0' from X server
>> 0
>>
>> On the VM it just hangs. Taskmanager shows xinit.exe waiting or hung
>> with XWin.exe churning cycles and eating memory; about 4kB a tick.
>>
>> Also on the VM, if I run the following:
>>
>> $ xinit -- -displayfd
>>
>> Then the display will open. So it seems to be an issue with whatever
>> code is dealing with the file descriptors.
>>
>>
>> Matt D.
>>
>> On 7/20/2014 9:06 PM, Matt D. wrote:
>>> The operating system is Windows XP Professional. It is a CLEAN install
>>> on a VMware virtual machine and is 100% patched up. Cygwin also is a
>>> clean install. I did try a rebaseall with no effect.
>>>
>>> This is the first time I've encountered this. When I run "xinit --
>>> -displayfd 3", xinit will hang and XWin takes up 100% of the cpu.
>>>
>>> I've confirmed that file descriptors are working:
>>>
>>> $ exec 3>a
>>> $ echo "test" >&3
>>> $ cat a
>>> test
>>> $ exec 3>&-
>>>
>>> I can confirm that ports are available and that both xinit and XWin work
>>> without this argument by running:
>>>
>>> $ xinit --
>>>
>>> Everything else works fine but without "-displayfd" I can't record where
>>> the display is for this session to disk.
>>>
>>> I've also tried copying known-working Cygwin installs into the VM and
>>> still have the same error. Copying the erroring install from the VM
>>> outside and running it on my development machine (Windows 7 x64) does
>>> not generate an error.
>>>
>>> Unless something stands out here, I can provide the VMware image for
>>> testing (how convenient).
>>>
>>>
>>> Matt D.
>>>
>>> --
>>> Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple
>>> Problem reports:       http://cygwin.com/problems.html
>>> Documentation:         http://x.cygwin.com/docs/
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>>>
>>>
>>>
>>
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>>
>>
>>
>
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>
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Re: xinit hangs on XWin infinite loop when using -displayfd

[Jon TURNEY]

Thanks for reporting this problem.

On 21/07/2014 18:30, Matt D. wrote:
> I found as a workaround to add the arguments "-nolisten tcp" when
> invoking xinit. However, I was under the impression that it was
> incompatible with -multiwindow and -clipboard, both of which seem to be
> working fine:
>
> https://cygwin.com/ml/cygwin-xfree/2009-05/msg00016.html

That restriction no longer exists.

https://cygwin.com/ml/cygwin-xfree/2009-10/msg00007.html

> On 7/21/2014 12:00 PM, Matt D. wrote:
>> Ok.. so I let xinit do its thing to see if it got anywhere. Eventually
>> it will pop and error box. Interestingly, I specified a displayfd value
>> of "3" and yet both the popup and the log are reporting "5":

This is expected.  xinit must know the display number of the X server it 
starts, so it can pass it on to any clients it starts, so it has a patch 
which should notice the -displayfd option, transparently use it to 
determine the display number for any clients they start, and then pass 
on the display number to the specified file descriptor

>> My XWin.0.log is about 15MB of repeated attempts to open a socket. Here
>> is a snippet. I hope this helps:
>>
>> InitConnectionLimits: MaxClients = 255
>> Welcome to the XWin X Server
>> Vendor: The Cygwin/X Project
>> Release: 1.15.1.0
>> OS: CYGWIN_NT-5.1 matthew-17ffb52 1.7.30(0.272/5/3) 2014-05-23 10:36 i686
>> OS: Windows XP Service Pack 3 [Windows NT 5.1 build 2600] (Win32)
>> Snapshot: 20140709-git-2e9c13ea41c51df7
>>
>> XWin was started with the following command line:
>>
>> X -displayfd 5
>>
>> ddxProcessArgument - Initializing default screens
>> winInitializeScreenDefaults - primary monitor w 1062 h 703
>> winInitializeScreenDefaults - native DPI x 96 y 96
>> ddxProcessArgument - arg: -displayfd
>> Trying to create socket for display number 0
>> _XSERVTransSocketOpenCOTSServer: Unable to open socket for inet6
>> _XSERVTransOpen: transport open failed for inet6/matthew-17ffb52:0
>> _XSERVTransMakeAllCOTSServerListeners: failed to open listener for inet6
>>
>> ..
>> Trying to create socket for display number 59534
>> _XSERVTransSocketOpenCOTSServer: Unable to open socket for inet6
>> _XSERVTransOpen: transport open failed for inet6/matthew-17ffb52:59534
>> _XSERVTransMakeAllCOTSServerListeners: failed to open listener for inet6
>> (EE) Fatal server error:
>> (EE) Failed to find a socket to listen on(EE)
>> [ 58128.390] (EE) Server terminated with error (1). Closing log file.

Ah.  So, it seems that we have checked all ports from 6000 to 59534 + 
6000 = 65534 and decided they are no good because we can't open an ipv6 
socket.

(It looks like there is another minor bug here in that we don't try port 
65535! :-))

I guess if you just run XWin, it reports that it can't create an inet6 
listener, but it continues anyway (unless the -nopn option is used).

But, the implementation of -displayfd requires that creating all the 
listener socket succeeds.  (It's not clear that this should be changed, 
otherwise we could reach the conclusion that it's ok to start a server 
on display n with a limited set of protocols, when a server already 
exists on display n with an non-intersecting set of protocols)

So, you may find that -nolisten inet6, rather than -nolisten tcp (which 
prevents both ipv4 and ipv6 listening) also works around the problem.

You might want to also investigate why inet6 sockets can't be opened.

-- 
Jon TURNEY
Volunteer Cygwin/X X Server maintainer

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Re: xinit hangs on XWin infinite loop when using -displayfd

[Matt D.]

Doh! I was so blind! Windows XP does not have an IPv6 protocol installed 
by default. I added it and the problem went away.

This sounds like a bug. XWin should verify whether a device which 
supports the target protocol exists before attempting to open a socket 
on it.

What is this used for? Sharing a local X session with someone else? 
Logging onto an existing X session at work from home? I've only ever 
used X locally or through ssh forwarding.


Matt D.

On 7/28/2014 8:34 AM, Jon TURNEY wrote:
>
> Thanks for reporting this problem.
>
> On 21/07/2014 18:30, Matt D. wrote:
>> I found as a workaround to add the arguments "-nolisten tcp" when
>> invoking xinit. However, I was under the impression that it was
>> incompatible with -multiwindow and -clipboard, both of which seem to be
>> working fine:
>>
>> https://cygwin.com/ml/cygwin-xfree/2009-05/msg00016.html
>
> That restriction no longer exists.
>
> https://cygwin.com/ml/cygwin-xfree/2009-10/msg00007.html
>
>> On 7/21/2014 12:00 PM, Matt D. wrote:
>>> Ok.. so I let xinit do its thing to see if it got anywhere. Eventually
>>> it will pop and error box. Interestingly, I specified a displayfd value
>>> of "3" and yet both the popup and the log are reporting "5":
>
> This is expected.  xinit must know the display number of the X server it
> starts, so it can pass it on to any clients it starts, so it has a patch
> which should notice the -displayfd option, transparently use it to
> determine the display number for any clients they start, and then pass
> on the display number to the specified file descriptor
>
>>> My XWin.0.log is about 15MB of repeated attempts to open a socket. Here
>>> is a snippet. I hope this helps:
>>>
>>> InitConnectionLimits: MaxClients = 255
>>> Welcome to the XWin X Server
>>> Vendor: The Cygwin/X Project
>>> Release: 1.15.1.0
>>> OS: CYGWIN_NT-5.1 matthew-17ffb52 1.7.30(0.272/5/3) 2014-05-23 10:36
>>> i686
>>> OS: Windows XP Service Pack 3 [Windows NT 5.1 build 2600] (Win32)
>>> Snapshot: 20140709-git-2e9c13ea41c51df7
>>>
>>> XWin was started with the following command line:
>>>
>>> X -displayfd 5
>>>
>>> ddxProcessArgument - Initializing default screens
>>> winInitializeScreenDefaults - primary monitor w 1062 h 703
>>> winInitializeScreenDefaults - native DPI x 96 y 96
>>> ddxProcessArgument - arg: -displayfd
>>> Trying to create socket for display number 0
>>> _XSERVTransSocketOpenCOTSServer: Unable to open socket for inet6
>>> _XSERVTransOpen: transport open failed for inet6/matthew-17ffb52:0
>>> _XSERVTransMakeAllCOTSServerListeners: failed to open listener for inet6
>>>
>>> ..
>>> Trying to create socket for display number 59534
>>> _XSERVTransSocketOpenCOTSServer: Unable to open socket for inet6
>>> _XSERVTransOpen: transport open failed for inet6/matthew-17ffb52:59534
>>> _XSERVTransMakeAllCOTSServerListeners: failed to open listener for inet6
>>> (EE) Fatal server error:
>>> (EE) Failed to find a socket to listen on(EE)
>>> [ 58128.390] (EE) Server terminated with error (1). Closing log file.
>
> Ah.  So, it seems that we have checked all ports from 6000 to 59534 +
> 6000 = 65534 and decided they are no good because we can't open an ipv6
> socket.
>
> (It looks like there is another minor bug here in that we don't try port
> 65535! :-))
>
> I guess if you just run XWin, it reports that it can't create an inet6
> listener, but it continues anyway (unless the -nopn option is used).
>
> But, the implementation of -displayfd requires that creating all the
> listener socket succeeds.  (It's not clear that this should be changed,
> otherwise we could reach the conclusion that it's ok to start a server
> on display n with a limited set of protocols, when a server already
> exists on display n with an non-intersecting set of protocols)
>
> So, you may find that -nolisten inet6, rather than -nolisten tcp (which
> prevents both ipv4 and ipv6 listening) also works around the problem.
>
> You might want to also investigate why inet6 sockets can't be opened.
>

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Re: xinit hangs on XWin infinite loop when using -displayfd

[Jon TURNEY]

On 29/07/2014 00:57, Matt D. wrote:
> Doh! I was so blind! Windows XP does not have an IPv6 protocol installed
> by default. I added it and the problem went away.
>
> This sounds like a bug. XWin should verify whether a device which
> supports the target protocol exists before attempting to open a socket
> on it.

Yes, it shouldn't fail like this if IPv6 isn't installed

I suspect the same problem will occur if you use X -displayfd built with 
IPv6 on linux kernel without IPv6 support

> What is this used for? Sharing a local X session with someone else?
> Logging onto an existing X session at work from home? I've only ever
> used X locally or through ssh forwarding.

It's used to allow remote X clients to connect to an X server without 
using a ssh tunnel (e.g. [1])

[1] 
http://x.cygwin.com/docs/ug/using-remote-apps.html#using-remote-apps-telnet

-- 
Jon TURNEY
Volunteer Cygwin/X X Server maintainer

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