Thanks for your feedback! Apologies it took some time for me
to incorporate this into another revision.
On 18-Jun 23:43, Martin KaFai Lau wrote:
> On Wed, Jun 17, 2020 at 10:29:38PM +0200, KP Singh wrote:
> > From: KP Singh <kpsingh@xxxxxxxxxx>
> >
> > Refactor the functionality in bpf_sk_storage.c so that concept of
> > storage linked to kernel objects can be extended to other objects like
> > inode, task_struct etc.
> >
> > bpf_sk_storage is updated to be bpf_local_storage with a union that
> > contains a pointer to the owner object. The type of the
> > bpf_local_storage can be determined using the newly added
> > bpf_local_storage_type enum.
> >
> > Each new local storage will still be a separate map and provide its own
> > set of helpers. This allows for future object specific extensions and
> > still share a lot of the underlying implementation.
> Thanks for taking up this effort to refactor sk_local_storage.
>
> I took a quick look. I have some comments and would like to explore
> some thoughts.
>
> > --- a/net/core/bpf_sk_storage.c
> > +++ b/kernel/bpf/bpf_local_storage.c
> > @@ -1,19 +1,22 @@
> > // SPDX-License-Identifier: GPL-2.0
> > /* Copyright (c) 2019 Facebook */
> > +#include "linux/bpf.h"
> > +#include "asm-generic/bug.h"
> > +#include "linux/err.h"
> "<" ">"
>
> > #include <linux/rculist.h>
> > #include <linux/list.h>
> > #include <linux/hash.h>
> > #include <linux/types.h>
> > #include <linux/spinlock.h>
> > #include <linux/bpf.h>
> > -#include <net/bpf_sk_storage.h>
> > +#include <linux/bpf_local_storage.h>
> > #include <net/sock.h>
> > #include <uapi/linux/sock_diag.h>
> > #include <uapi/linux/btf.h>
> >
> > static atomic_t cache_idx;
> inode local storage and sk local storage probably need a separate
> cache_idx. An improvement on picking cache_idx has just been
> landed also.
I see, thanks! I rebased and I now see that cache_idx is now a:
static u64 cache_idx_usage_counts[BPF_STORAGE_CACHE_SIZE];
which tracks the free cache slots rather than using a single atomic
cache_idx. I guess all types of local storage can share this now
right?
>
> [ ... ]
>
> > +struct bpf_local_storage {
> > + struct bpf_local_storage_data __rcu *cache[BPF_STORAGE_CACHE_SIZE];
> > return NULL;
[...]
> > }
> >
> > -/* sk_storage->lock must be held and selem->sk_storage == sk_storage.
> > +static void __unlink_local_storage(struct bpf_local_storage *local_storage,
> > + bool uncharge_omem)
> Nit. indent is off. There are a few more cases like this.
Thanks, will fix this. (note to self: don't trust the editor's
clang-format blindly).
>
> > +{
> > + struct sock *sk;
> > +
> > + switch (local_storage->stype) {
> Does it need a new bpf_local_storage_type? Is map_type as good?
>
> Instead of adding any new member (e.g. stype) to
> "struct bpf_local_storage", can the smap pointer be directly used
> here instead?
>
> For example in __unlink_local_storage() here, it should
> have a hold to the selem which then has a hold to smap.
Good point, Updated to using the map->map_type.
>
> > + case BPF_LOCAL_STORAGE_SK:
> > + sk = local_storage->sk;
> > + if (uncharge_omem)
> > + atomic_sub(sizeof(struct bpf_local_storage),
> > + &sk->sk_omem_alloc);
> > +
> > + /* After this RCU_INIT, sk may be freed and cannot be used */
> > + RCU_INIT_POINTER(sk->sk_bpf_storage, NULL);
> > + local_storage->sk = NULL;
> > + break;
> > + }
> Another thought on the stype switch cases.
>
> Instead of having multiple switches on stype in bpf_local_storage.c which may
> not be scalable soon if we are planning to support a few more kernel objects,
> have you considered putting them into its own "ops". May be a few new
> ops can be added to bpf_map_ops to do local storage unlink/update/alloc...etc.
Good idea, I was able to refactor this with the following ops:
/* Functions called by bpf_local_storage maps */
void (*map_local_storage_unlink)(struct bpf_local_storage *local_storage,
bool uncharge_omem);
struct bpf_local_storage_elem *(*map_selem_alloc)(
struct bpf_local_storage_map *smap, void *owner, void *value,
bool charge_omem);
struct bpf_local_storage_data *(*map_local_storage_update)(
void *owner, struct bpf_map *map, void *value, u64 flags);
int (*map_local_storage_alloc)(void *owner,
struct bpf_local_storage_map *smap,
struct bpf_local_storage_elem *elem);
Let me know if you have any particular thoughts/suggestions about
this.
>
> > +}
> > +
> > +/* local_storage->lock must be held and selem->local_storage == local_storage.
> > * The caller must ensure selem->smap is still valid to be
> > * dereferenced for its smap->elem_size and smap->cache_idx.
> > + *
> > + * uncharge_omem is only relevant when:
[...]
> > + /* bpf_local_storage_map is currently limited to CAP_SYS_ADMIN as
> > * the map_alloc_check() side also does.
> > */
> > if (!bpf_capable())
> > @@ -1025,10 +1127,10 @@ bpf_sk_storage_diag_alloc(const struct nlattr *nla_stgs)
> > }
> > EXPORT_SYMBOL_GPL(bpf_sk_storage_diag_alloc);
> Would it be cleaner to leave bpf_sk specific function, map_ops, and func_proto
> in net/core/bpf_sk_storage.c?
Sure, I can also keep the sk_clone code their as well for now.
>
> There is a test in map_tests/sk_storage_map.c, in case you may not notice.
I will try to make it generic as a part of this series. If it takes
too much time, I will send a separate patch for testing
inode_storage_map and till then we have some assurance with
test_local_storage in test_progs.
- KP
