On Sun, Mar 20, 2022 at 01:01:16AM IST, Kumar Kartikeya Dwivedi wrote:
> On Sat, Mar 19, 2022 at 11:25:34PM IST, Alexei Starovoitov wrote:
> > On Thu, Mar 17, 2022 at 05:29:44PM +0530, Kumar Kartikeya Dwivedi wrote:
> > > Next commit's field type will not be struct, but pointer, and it will
> > > not be limited to one offset, but multiple ones. Make existing
> > > btf_find_struct_field and btf_find_datasec_var functions amenable to use
> > > for finding BTF ID pointers in map value, by taking a moving spin_lock
> > > and timer specific checks into their own function.
> > >
> > > The alignment, and name are checked before the function is called, so it
> > > is the last point where we can skip field or return an error before the
> > > next loop iteration happens. This is important, because we'll be
> > > potentially reallocating memory inside this function in next commit, so
> > > being able to do that when everything else is in order is going to be
> > > more convenient.
> > >
> > > The name parameter is now optional, and only checked if it is not NULL.
> > >
> > > The size must be checked in the function, because in case of PTR it will
> > > instead point to the underlying BTF ID it is pointing to (or modifiers),
> > > so the check becomes wrong to do outside of function, and the base type
> > > has to be obtained by removing modifiers.
> > >
> > > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
> > > ---
> > > kernel/bpf/btf.c | 120 +++++++++++++++++++++++++++++++++--------------
> > > 1 file changed, 86 insertions(+), 34 deletions(-)
> > >
> > > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > > index 17b9adcd88d3..5b2824332880 100644
> > > --- a/kernel/bpf/btf.c
> > > +++ b/kernel/bpf/btf.c
> > > @@ -3161,71 +3161,109 @@ static void btf_struct_log(struct btf_verifier_env *env,
> > > btf_verifier_log(env, "size=%u vlen=%u", t->size, btf_type_vlen(t));
> > > }
> > >
> > > +enum {
> > > + BTF_FIELD_SPIN_LOCK,
> > > + BTF_FIELD_TIMER,
> > > +};
> > > +
> > > +struct btf_field_info {
> > > + u32 off;
> > > +};
> > > +
> > > +static int btf_find_field_struct(const struct btf *btf, const struct btf_type *t,
> > > + u32 off, int sz, struct btf_field_info *info)
> > > +{
> > > + if (!__btf_type_is_struct(t))
> > > + return 0;
> > > + if (t->size != sz)
> > > + return 0;
> > > + if (info->off != -ENOENT)
> > > + /* only one such field is allowed */
> > > + return -E2BIG;
> > > + info->off = off;
> > > + return 0;
> > > +}
> > > +
> > > static int btf_find_struct_field(const struct btf *btf, const struct btf_type *t,
> > > - const char *name, int sz, int align)
> > > + const char *name, int sz, int align, int field_type,
> > > + struct btf_field_info *info)
> > > {
> > > const struct btf_member *member;
> > > - u32 i, off = -ENOENT;
> > > + u32 i, off;
> > > + int ret;
> > >
> > > for_each_member(i, t, member) {
> > > const struct btf_type *member_type = btf_type_by_id(btf,
> > > member->type);
> > > - if (!__btf_type_is_struct(member_type))
> > > - continue;
> > > - if (member_type->size != sz)
> > > - continue;
> > > - if (strcmp(__btf_name_by_offset(btf, member_type->name_off), name))
> > > - continue;
> > > - if (off != -ENOENT)
> > > - /* only one such field is allowed */
> > > - return -E2BIG;
> > > +
> > > off = __btf_member_bit_offset(t, member);
> > > +
> > > + if (name && strcmp(__btf_name_by_offset(btf, member_type->name_off), name))
> > > + continue;
> > > if (off % 8)
> > > /* valid C code cannot generate such BTF */
> > > return -EINVAL;
> > > off /= 8;
> > > if (off % align)
> > > return -EINVAL;
> > > +
> > > + switch (field_type) {
> > > + case BTF_FIELD_SPIN_LOCK:
> > > + case BTF_FIELD_TIMER:
> >
> > Since spin_lock vs timer is passed into btf_find_struct_field() as field_type
> > argument there is no need to pass name, sz, align from the caller.
> > Pls make btf_find_spin_lock() to pass BTF_FIELD_SPIN_LOCK only
> > and in the above code do something like:
> > switch (field_type) {
> > case BTF_FIELD_SPIN_LOCK:
> > name = "bpf_spin_lock";
> > sz = ...
> > break;
> > case BTF_FIELD_TIMER:
> > name = "bpf_timer";
> > sz = ...
> > break;
> > }
>
> Would doing this in btf_find_field be better? Then we set these once instead of
> doing it twice in btf_find_struct_field, and btf_find_datasec_var.
>
> > switch (field_type) {
> > case BTF_FIELD_SPIN_LOCK:
> > case BTF_FIELD_TIMER:
> > if (!__btf_type_is_struct(member_type))
> > continue;
> > if (strcmp(__btf_name_by_offset(btf, member_type->name_off), name))
> > ...
> > btf_find_field_struct(btf, member_type, off, sz, info);
> > }
> >
> > It will cleanup the later patch which passes NULL, sizeof(u64), alignof(u64)
> > only to pass something into the function.
> > With above suggestion it wouldn't need to pass dummy args. BTF_FIELD_KPTR will be enough.
> >
Just to be clear, for the kptr case we still use size and align, only name is
optional. size is used for datasec_var call, align is used in both struct_field
and datasec_var. So I'm not sure whether moving it around has much effect,
instead of the caller it will now be set based on field_type inside
btf_find_field.
> > > + ret = btf_find_field_struct(btf, member_type, off, sz, info);
> > > + if (ret < 0)
> > > + return ret;
> > > + break;
> > > + default:
> > > + return -EFAULT;
> > > + }
> > > }
> > > - return off;
> > > + return 0;
> > > }
> > >
> > > static int btf_find_datasec_var(const struct btf *btf, const struct btf_type *t,
> > > - const char *name, int sz, int align)
> > > + const char *name, int sz, int align, int field_type,
> > > + struct btf_field_info *info)
> > > {
> > > const struct btf_var_secinfo *vsi;
> > > - u32 i, off = -ENOENT;
> > > + u32 i, off;
> > > + int ret;
> > >
> > > for_each_vsi(i, t, vsi) {
> > > const struct btf_type *var = btf_type_by_id(btf, vsi->type);
> > > const struct btf_type *var_type = btf_type_by_id(btf, var->type);
> > >
> > > - if (!__btf_type_is_struct(var_type))
> > > - continue;
> > > - if (var_type->size != sz)
> > > + off = vsi->offset;
> > > +
> > > + if (name && strcmp(__btf_name_by_offset(btf, var_type->name_off), name))
> > > continue;
> > > if (vsi->size != sz)
> > > continue;
> > > - if (strcmp(__btf_name_by_offset(btf, var_type->name_off), name))
> > > - continue;
> > > - if (off != -ENOENT)
> > > - /* only one such field is allowed */
> > > - return -E2BIG;
> > > - off = vsi->offset;
> > > if (off % align)
> > > return -EINVAL;
> > > +
> > > + switch (field_type) {
> > > + case BTF_FIELD_SPIN_LOCK:
> > > + case BTF_FIELD_TIMER:
> > > + ret = btf_find_field_struct(btf, var_type, off, sz, info);
> > > + if (ret < 0)
> > > + return ret;
> > > + break;
> > > + default:
> > > + return -EFAULT;
> > > + }
> > > }
> > > - return off;
> > > + return 0;
> > > }
> > >
> > > static int btf_find_field(const struct btf *btf, const struct btf_type *t,
> > > - const char *name, int sz, int align)
> > > + const char *name, int sz, int align, int field_type,
> > > + struct btf_field_info *info)
> > > {
> > > -
> > > if (__btf_type_is_struct(t))
> > > - return btf_find_struct_field(btf, t, name, sz, align);
> > > + return btf_find_struct_field(btf, t, name, sz, align, field_type, info);
> > > else if (btf_type_is_datasec(t))
> > > - return btf_find_datasec_var(btf, t, name, sz, align);
> > > + return btf_find_datasec_var(btf, t, name, sz, align, field_type, info);
> > > return -EINVAL;
> > > }
> > >
> > > @@ -3235,16 +3273,30 @@ static int btf_find_field(const struct btf *btf, const struct btf_type *t,
> > > */
> > > int btf_find_spin_lock(const struct btf *btf, const struct btf_type *t)
> > > {
> > > - return btf_find_field(btf, t, "bpf_spin_lock",
> > > - sizeof(struct bpf_spin_lock),
> > > - __alignof__(struct bpf_spin_lock));
> > > + struct btf_field_info info = { .off = -ENOENT };
> > > + int ret;
> > > +
> > > + ret = btf_find_field(btf, t, "bpf_spin_lock",
> > > + sizeof(struct bpf_spin_lock),
> > > + __alignof__(struct bpf_spin_lock),
> > > + BTF_FIELD_SPIN_LOCK, &info);
> > > + if (ret < 0)
> > > + return ret;
> > > + return info.off;
> > > }
> > >
> > > int btf_find_timer(const struct btf *btf, const struct btf_type *t)
> > > {
> > > - return btf_find_field(btf, t, "bpf_timer",
> > > - sizeof(struct bpf_timer),
> > > - __alignof__(struct bpf_timer));
> > > + struct btf_field_info info = { .off = -ENOENT };
> > > + int ret;
> > > +
> > > + ret = btf_find_field(btf, t, "bpf_timer",
> > > + sizeof(struct bpf_timer),
> > > + __alignof__(struct bpf_timer),
> > > + BTF_FIELD_TIMER, &info);
> > > + if (ret < 0)
> > > + return ret;
> > > + return info.off;
> > > }
> > >
> > > static void __btf_struct_show(const struct btf *btf, const struct btf_type *t,
> > > --
> > > 2.35.1
> > >
> >
> > --
>
> --
> Kartikeya
--
Kartikeya
