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

[ranjith krishnan]

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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