helpers: linux: fs: use mount rbtree instead of list

[morbidrsa]

Starting with kernel v6.8 the mnt_list int struct mnt_namespace git converted to a rb-tree.

Reflect this change in drgn's for_each_mount() helper.

[osandov]

Thanks, Johannes! Could you please also keep a fallback for the old kernel version? for_each_vma() is a good example of how to do that:

drgn/drgn/helpers/linux/mm.py

Lines 1219 to 1232 in 145ac79

	try:
	# Since Linux kernel commit 763ecb035029 ("mm: remove the vma linked
	# list") (in v6.1), VMAs are stored in a maple tree.
	mt = mm.mm_mt.address_of_()
	except AttributeError:
	# Before that, they are in a linked list.
	vma = mm.mmap
	while vma:
	yield vma
	vma = vma.vm_next
	else:
	type = mm.prog_.type("struct vm_area_struct *")
	for _, _, entry in mt_for_each(mt):
	yield cast(type, entry)

. CONTRIBUTING.rst also has a Linux Kernel Helpers section.

[morbidrsa]

Sure will send an update soon

[osandov]

Here's another example I just had to do: 718da44. Let me know if you need any more pointers or if you'd like me to take it from here.

[morbidrsa]

Here's another example I just had to do: 718da44. Let me know if you need any more pointers or if you'd like me to take it from here.

Hi Omar, no there's no problem, I just didn't have time to do the update. I'm stuck debugging a btrfs issue.

[osandov]

Thanks! Just a couple of nits.

[osandov]

Just a couple of nits documented in CONTRIBUTING.rst:

1. Add a comment documenting the version divergence.
2. Put the case for the latest kernel first.

Suggested change

	try:
	mounts = list_for_each_entry("struct mount", ns.list.address_of_(), "mnt_list")
	except AttributeError:
	mounts = rbtree_inorder_for_each_entry(
	"struct mount", ns.mounts.address_of_(), "mnt_node"
	)
	# Since Linux kernel commit 2eea9ce4310d ("mounts: keep list of mounts in
	# an rbtree") (in v6.8), the mounts in a namespace are in a red-black tree.
	# Before that, they're in a list.
	try:
	mounts = rbtree_inorder_for_each_entry(
	"struct mount", ns.mounts.address_of_(), "mnt_node"
	)
	except AttributeError:
	mounts = list_for_each_entry("struct mount", ns.list.address_of_(), "mnt_list")

[morbidrsa]

Unfortunately that made the CI unhappy when I tried it.

[osandov]

Ah, I see, struct mnt_namespace previously had a member named mounts which was the number of mounts, so the AttributeError doesn't trigger in the try. Okay, let's just add the comment.

[osandov]

I have a related fix for path_lookup(), so I'll add the comment on my end. Thanks!