> walk through some linked list {
> for each element take a bit thereof and append to supplied user buf
> }
>
> If I wished to protect the linked list with a spinlock I need to redesign
> the loop and the only way I can think of is to temporarily store those
> elements in kernel buffer and then copy the lot to userspace. But as the
> size of the acumulated buffers is not known in advance the whole thing is
> not as trivial as it should be.
the problem itself is the nontrivial one. You are trying to take a
spinlock-protected 'snapshot' of an indefinit-length kernel-space object,
and that is a nontrivial concept. The 'easy' solution is to give up
atomicity.
> (in particular, I was thinking about qm_modules() that copies
> module->name to user buffer one at a time and I wanted to protect
> module_list with a rw spinlock, taking read_lock in this case).
do you really need atomicity of the list? There are many places in the
kernel which have a spinlock-protected loop, and once they have the
potential to sleep they drop the lock and restart the loop.
truncate_inode_pages() is one example.
-- mingo
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