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Message-ID: <20181112232925.74cajfncscaf7sc6@mini-arch>
Date: Mon, 12 Nov 2018 15:29:25 -0800
From: Stanislav Fomichev <sdf@...ichev.me>
To: Martin Lau <kafai@...com>
Cc: Stanislav Fomichev <sdf@...gle.com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
"ast@...nel.org" <ast@...nel.org>,
"daniel@...earbox.net" <daniel@...earbox.net>,
"shuah@...nel.org" <shuah@...nel.org>,
"jakub.kicinski@...ronome.com" <jakub.kicinski@...ronome.com>,
"quentin.monnet@...ronome.com" <quentin.monnet@...ronome.com>,
Roman Gushchin <guro@...com>,
"jiong.wang@...ronome.com" <jiong.wang@...ronome.com>,
"bhole_prashant_q7@....ntt.co.jp" <bhole_prashant_q7@....ntt.co.jp>,
"john.fastabend@...il.com" <john.fastabend@...il.com>,
"jbenc@...hat.com" <jbenc@...hat.com>,
"treeze.taeung@...il.com" <treeze.taeung@...il.com>,
Yonghong Song <yhs@...com>, Okash Khawaja <osk@...com>,
"sandipan@...ux.vnet.ibm.com" <sandipan@...ux.vnet.ibm.com>
Subject: Re: [PATCH v5 bpf-next 2/7] libbpf: cleanup after partial failure in
bpf_object__pin
On 11/12, Martin Lau wrote:
> On Mon, Nov 12, 2018 at 02:10:11PM -0800, Stanislav Fomichev wrote:
> > On 11/12, Martin Lau wrote:
> > > On Fri, Nov 09, 2018 at 08:21:41AM -0800, Stanislav Fomichev wrote:
> > > [ ... ]
> > > > @@ -1918,23 +2160,20 @@ void *bpf_object__priv(struct bpf_object *obj)
> > > > }
> > > >
> > > > static struct bpf_program *
> > > > -__bpf_program__next(struct bpf_program *prev, struct bpf_object *obj)
> > > > +__bpf_program__iter(struct bpf_program *p, struct bpf_object *obj, int i)
> > > > {
> > > > - size_t idx;
> > > > + ssize_t idx;
> > > >
> > > > if (!obj->programs)
> > > > return NULL;
> > > > - /* First handler */
> > > > - if (prev == NULL)
> > > > - return &obj->programs[0];
> > > >
> > > > - if (prev->obj != obj) {
> > > > + if (p->obj != obj) {
> > > > pr_warning("error: program handler doesn't match object\n");
> > > > return NULL;
> > > > }
> > > >
> > > > - idx = (prev - obj->programs) + 1;
> > > > - if (idx >= obj->nr_programs)
> > > > + idx = (p - obj->programs) + i;
> > > > + if (idx >= obj->nr_programs || idx < 0)
> > > > return NULL;
> > > > return &obj->programs[idx];
> > > > }
> > > > @@ -1944,8 +2183,29 @@ bpf_program__next(struct bpf_program *prev, struct bpf_object *obj)
> > > > {
> > > > struct bpf_program *prog = prev;
> > > >
> > > > + if (prev == NULL)
> > > > + return obj->programs;
> > > > +
> > > This patch breaks the behavior introduced in
> > > commit eac7d84519a3 ("tools: libbpf: don't return '.text' as a program for multi-function programs"):
> > > "Make bpf_program__next() skip over '.text' section if object file
> > > has pseudo calls. The '.text' section is hardly a program in that
> > > case, it's more of a storage for code of functions other than main."
> > >
> > > For example, the userspace could have been doing:
> > > prog = bpf_program__next(NULL, obj);
> > > bpf_program__set_type(prog, BPF_PROG_TYPE_TRACEPOINT);
> > > bpf_object__load(obj);
> > >
> > > For the bpf_prog.o that has pseudo calls, after this patch in bpf-next,
> > > the prog returned by bpf_program__next() could be in ".text" instead of
> > > the main bpf program. The next bpf_program__set_type() has
> > > no effect to the main program. The following bpf_object__load()
> > > will catch user in surprise with the main bpf prog in
> > > the wrong BPF_PROG_TYPE.
> >
> > Will something like the following fix your concern? (plus, assuming the
> > same for prev):
> >
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -2216,8 +2216,11 @@ bpf_program__next(struct bpf_program *prev, struct bpf_object *obj)
> > {
> > struct bpf_program *prog = prev;
> >
> > - if (prev == NULL)
> > - return obj->programs;
> > + if (prev == NULL) {
> > + prog = obj->programs;
> > + if (!prog || !bpf_program__is_function_storage(prog, obj))
> > + return prog;
> > + }
> >
> > do {
> > prog = __bpf_program__iter(prog, obj, 1);
> >
> > Any suggestions for a better way to do it?
> I think that would work. The bpf_program__prev() will need the same
> treatment though...
>
> Here is my mostly untested fix to unblock my other dev works. It moves
> the very first NULL check back to __bpf_program__iter():
I like your version and it works with my simple flow dissector test :-)
Thanks for spotting and fixing it!
> From de1c89ae1768e756825a6874268b5b1686695c93 Mon Sep 17 00:00:00 2001
> From: Martin KaFai Lau <kafai@...com>
> Date: Mon, 12 Nov 2018 14:52:39 -0800
> Subject: [PATCH] bpf: libbpf: Fix bpf_program__next() API
>
> This patch restores the behavior in
> commit eac7d84519a3 ("tools: libbpf: don't return '.text' as a program for multi-function programs"):
> such that bpf_program__next() does not return pseudo programs in ".text".
>
> Fixes: 0c19a9fbc9cd ("libbpf: cleanup after partial failure in bpf_object__pin")
> Signed-off-by: Martin KaFai Lau <kafai@...com>
> ---
> tools/lib/bpf/libbpf.c | 25 +++++++++++--------------
> 1 file changed, 11 insertions(+), 14 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index e827542ffa3a..a01eb9584e52 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -2193,19 +2193,25 @@ void *bpf_object__priv(struct bpf_object *obj)
> }
>
> static struct bpf_program *
> -__bpf_program__iter(struct bpf_program *p, struct bpf_object *obj, int i)
> +__bpf_program__iter(struct bpf_program *p, struct bpf_object *obj, bool forward)
> {
> + size_t nr_programs = obj->nr_programs;
> ssize_t idx;
>
> - if (!obj->programs)
> + if (!nr_programs)
> return NULL;
>
> + if (!p)
> + /* Iter from the beginning */
> + return forward ? &obj->programs[0] :
> + &obj->programs[nr_programs - 1];
> +
> if (p->obj != obj) {
> pr_warning("error: program handler doesn't match object\n");
> return NULL;
> }
>
> - idx = (p - obj->programs) + i;
> + idx = (p - obj->programs) + (forward ? 1 : -1);
> if (idx >= obj->nr_programs || idx < 0)
> return NULL;
> return &obj->programs[idx];
> @@ -2216,11 +2222,8 @@ bpf_program__next(struct bpf_program *prev, struct bpf_object *obj)
> {
> struct bpf_program *prog = prev;
>
> - if (prev == NULL)
> - return obj->programs;
> -
> do {
> - prog = __bpf_program__iter(prog, obj, 1);
> + prog = __bpf_program__iter(prog, obj, true);
> } while (prog && bpf_program__is_function_storage(prog, obj));
>
> return prog;
> @@ -2231,14 +2234,8 @@ bpf_program__prev(struct bpf_program *next, struct bpf_object *obj)
> {
> struct bpf_program *prog = next;
>
> - if (next == NULL) {
> - if (!obj->nr_programs)
> - return NULL;
> - return obj->programs + obj->nr_programs - 1;
> - }
> -
> do {
> - prog = __bpf_program__iter(prog, obj, -1);
> + prog = __bpf_program__iter(prog, obj, false);
> } while (prog && bpf_program__is_function_storage(prog, obj));
>
> return prog;
> --
> 2.17.1
>
> >
> > > > do {
> > > > - prog = __bpf_program__next(prog, obj);
> > > > + prog = __bpf_program__iter(prog, obj, 1);
> > > > + } while (prog && bpf_program__is_function_storage(prog, obj));
> > > > +
> > > > + return prog;
> > > > +}
> > > > +
> > > > +struct bpf_program *
> > > > +bpf_program__prev(struct bpf_program *next, struct bpf_object *obj)
> > > > +{
> > > > + struct bpf_program *prog = next;
> > > > +
> > > > + if (next == NULL) {
> > > > + if (!obj->nr_programs)
> > > > + return NULL;
> > > > + return obj->programs + obj->nr_programs - 1;
> > > > + }
> > > > +
> > > > + do {
> > > > + prog = __bpf_program__iter(prog, obj, -1);
> > > > } while (prog && bpf_program__is_function_storage(prog, obj));
> > > >
> > > > return prog;
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