[Xen-devel] How to log system calls from a PV DomU under Xen

[ranjith krishnan <ranjithkrishnan1@xxxxxxxxx>]

Hello, 

I was posting a couple weeks back here, asking questions about getting DomUs working in Xen when installing Xen from source. 

Well, I have managed to get things working. Currently my setup is like this now.

Xen 4.2.2, installed from source, 

Fedora 18 Dom0 x86_64, Debian 6 PV DomU x86_64, and Ubuntu 12.04 HVM DomU x86_64. 

My processor has Intel VT-X enabled.

I  used xl/xm to create DomUs. I was unable to get virt-manager working to create guests.

I faced a similar problem with Xen 4.1 and Fedora 17 earlier. 

As the next step in my project, I want to log some system call information. 

Basically, every time a system call is made in my PV DomU, I just want to print a line like "System call made from DomU, systemcall id = xx". That is all I need for now. 

I have some questions regarding the same. 

1. This might be a stupid question, but here goes.

After I modify source code, should I do the whole compilation/install process to see my changes. 

ie. should i do "make and install xen, tools and stubdom" or will "make and install xen" suffice ?

2. How is the system call flow happening in Xen?

 Where in the code is the system call being intercepted by the hypervisor for a PV DomU. ?

I found some information from this paper, http://hal.archives-ouvertes.fr/docs/00/43/10/31/PDF/Technical_Report_Syscall_Interception.pdf

but still am not clear about the whole picture.

Is there documentation available explaining for how system calls are handled in Xen ?

The Xen code is quite large, and I am sorry to say I get lost reading it without some kind of knowledge.

3. How to log data?

I see printk statements in the code. Are printk statements tied to a certain logging level ? Should I add "loglvl=all guest_loglvl=all" to my Dom0 grub to see the output from printk statements ?

Also, which output file should I be seeing for my scenario?

/var/log/xen/xend.log ?

I apologize for the long email. 
Please take some time out and kindly reply. 

--
Ranjith krishnan

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