libvirt users - Aug 2012 - Where does "cmd" initailize in qemu_command.c?

Hi,

         Excuse me, I have a question when I reading the libvirt source
codes.

         I have known the process of how libvirt start/manage qemu, since I
need to write a driver based on libvirt. But one thing also confused, please
give me some tips.

         1.

In qemu_command.c, there is a function call "cmd
virCommandNewArgList(emulator, "-S", NULL);", which initializes
pointer
"cmd". However, I don't find the initial value of
"cmd->args", which
represents the input of virFindFileInPath in Util.c. Through
virFindFileInPath, one could find a requested executable file in the PATH
env to start specified hypervisors. 

So could you please tell me what the value of args[0] is? Or where does
cmd->args initialize?

         2.

         In qemu_driver.c, there is a function call "vm
virDomainFindByUUID(&driver->domains, dom->uuid);", whose
returned value
"vm" is important in the next functions. Then we could get the
"vm"'s value
in hash.c which is the end part to lookup domains saved in hashtable. 

May I know where does HashTable initialize? I mean where can I set the
hashtable's values in detail, if I want to modify some values?

         3.

         This might be the same as question 1.

         In command.c, "execve(cmd->args[0], cmd->args,
cmd->env)" is a way
to exec command. About qemu_driver, what is the value of those three inputs?


 

         Thanks a lot!

 

         Regard,

         Corey

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On 08/16/2012 10:52 AM, He Xin wrote:
> 
> In qemu_command.c, there is a function call "cmd >
virCommandNewArgList(emulator, "-S", NULL);", which initializes
pointer
> "cmd". However, I don't find the initial value of
"cmd->args", which
> represents the input of virFindFileInPath in Util.c. Through
> virFindFileInPath, one could find a requested executable file in the PATH
> env to start specified hypervisors. 
> 
> So could you please tell me what the value of args[0] is? Or where does
> cmd->args initialize?
cmd->args is initialized by the constructor - in this case, you are
using the virCommandNewArgList constructor, so cmd->args[0] will be a
copy of your 'emulator' parameter.  So, you merely need trace back up
the call stack to see where 'emulator' was first determined (hint: it
came from virDomainDefPtr def->emulator, which was populated during
virDomainDefParseXML to either match the explicit <emulator> tag in your
XML or fall back to the default stored in the virCapsPtr caps structure).
>          In qemu_driver.c, there is a function call "vm >
virDomainFindByUUID(&driver->domains, dom->uuid);", whose
returned value
> "vm" is important in the next functions. Then we could get the
"vm"'s value
> in hash.c which is the end part to lookup domains saved in hashtable. 
> 
> May I know where does HashTable initialize? I mean where can I set the
> hashtable's values in detail, if I want to modify some values?
The &driver->domains hash table is manipulated via functions in
src/conf/domain_conf.c.
> 
>          3.
> 
>          This might be the same as question 1.
> 
>          In command.c, "execve(cmd->args[0], cmd->args,
cmd->env)" is a way
> to exec command. About qemu_driver, what is the value of those three
inputs?
Yes, this is the same as question 1 - these values are determined by all
the calls to the virCommand* functions acting on the cmd structure.

Your questions seem to be more of a development nature about the libvirt
source code, and less of a user nature about how to use the API in using
the libvirt as a library in your own code.  As such, you should probably
take future questions of this nature to libvir-lists at redhat.com.

-- 
Eric Blake   eblake at redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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