Hi,
This is the first time I am trying to understand the
Linux kernel. To do so, I have started to read the
following book by Robert Love
Linux Kernel Development, Second Edition. Since the
book refers to 2.6.10, I am browsing this version.
On Page 30 of the book, it says,
"Similarly, it is possible to iterate over a
processe's children with
struct task_struct *task;
struct list_head *list;
list_for_each(list, ¤t->children) {
task = list_entry(list,struct task_struct,
sibling);
/* task now points to one of current's children */
}"
>From what I understand, list_for_each above will
iterate through one of the current processes child (if
there was one), then that childs child(if there is
one) and so on. Am I right in concluding this? This
means only the first iteration will find the current
processes child.
Also with respect to the list_entry macro, since list
points to the children member of the child task and
list_entry uses macro container_of from
linux/kernel.h, task cannot point to the task_struct
of the child because list_entry subtracts the offset
of sibling member from the address of the children
member. This will subtract more than is necessary. So,
the first argument of list_entry should point to a
list head member with the same member name within the
struct. Otherwise it will not return the address of
the containing struct. Am I right in concluding this?
>From what I understand browsing through the kernel
source, the only way to iterate through a processes
children is by asking a child to iterate through its
siblings. Am I right?
So the code snippet would have to be,
struct task_struct *task;
struct list_head *list;
if(current != (task =
list_entry((current->children).next, struct
task_struct, children)))
{
/* task one of current processes child. Find the
other children */
list_for_each(list, &task->sibling)
{
task = list_entry(list, struct task_struct,
sibling);
/* For each iteration of the loop, task contains
other children of the current process */
}
}
else
{
/* there are no children. task points to the
current processes task_struct */
}
I would appreciate it if some body could clarify this.
Am I missing something here?
Thanks
Vish
__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around
http://mail.yahoo.com
--
Kernelnewbies: Help each other learn about the Linux kernel.
Archive: http://mail.nl.linux.org/kernelnewbies/
FAQ: http://kernelnewbies.org/faq/
