Hi,
> In function do_fork (), i see that we allocate some pidmap.
> Could someone please tell me -
> what is pidmap ?
> what is its use?
>
While creating a new process, we need to allocate and initialize a "struct pid" for it. In alloc_pid(), the kernel tries to allocate & initialize the fields of struct pid. One of the fields ("nr") is the actual NUMERIC pid (visible to user and for all other purposes) and it is initialized using alloc_pidmap().
The pidmap is just an efficient way to keep track of which all process IDs (numbers) are in use and which ones are not. Basically we keep a bitmap of all the possible PIDs (1 bit for each PID). The bit is set/unset depending upon whether the PID is alloted to some process or not. alloc_pid() determines the number by simply checking the first bit that is set in the map.
Thanks,
Rajat
--
To unsubscribe from this list: send an email with
"unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx
Please read the FAQ at http://kernelnewbies.org/FAQ
