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
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