Allow some BPF program types to support auto-attach only in subste of
cases. Currently, if some BPF program type specifies attach callback, it
is assumed that during skeleton attach operation all such programs
either successfully attach or entire skeleton attachment fails. If some
program doesn't support auto-attachment from skeleton, such BPF program
types shouldn't have attach callback specified.
This is limiting for cases when, depending on how full the SEC("")
definition is, there could either be enough details to support
auto-attach or there might not be and user has to use some specific API
to provide more details at runtime.
One specific example of such desired behavior might be SEC("uprobe"). If
it's specified as just uprobe auto-attach isn't possible. But if it's
SEC("uprobe/<some_binary>:<some_func>") then there are enough details to
support auto-attach. Note that there is a somewhat subtle difference
between auto-attach behavior of BPF skeleton and using "generic"
bpf_program__attach(prog) (which uses the same attach handlers under the
cover). Skeleton allow some programs within bpf_object to not have
auto-attach implemented and doesn't treat that as an error. Instead such
BPF programs are just skipped during skeleton's (optional) attach step.
bpf_program__attach(), on the other hand, is called when user *expects*
auto-attach to work, so if specified program doesn't implement or
doesn't support auto-attach functionality, that will be treated as an
error.
Another improvement to the way libbpf is handling SEC()s would be to not
require providing dummy kernel function name for kprobe. Currently,
SEC("kprobe/whatever") is necessary even if actual kernel function is
determined by user at runtime and bpf_program__attach_kprobe() is used
to specify it. With changes in this patch, it's possible to support both
SEC("kprobe") and SEC("kprobe/<actual_kernel_function"), while only in
the latter case auto-attach will be performed. In the former one, such
kprobe will be skipped during skeleton attach operation.
Reviewed-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
---
tools/lib/bpf/libbpf.c | 116 ++++++++++++++++++++++++++---------------
1 file changed, 73 insertions(+), 43 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 2262bcdfee92..c4acb72d3c7e 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -201,11 +201,12 @@ struct reloc_desc {
};
};
-struct bpf_sec_def;
-
-typedef int (*init_fn_t)(struct bpf_program *prog, long cookie);
-typedef int (*preload_fn_t)(struct bpf_program *prog, struct bpf_prog_load_opts *opts, long cookie);
-typedef struct bpf_link *(*attach_fn_t)(const struct bpf_program *prog, long cookie);
+typedef int (*libbpf_prog_init_fn_t)(struct bpf_program *prog, long cookie);
+typedef int (*libbpf_prog_preload_fn_t)(struct bpf_program *prog,
+ struct bpf_prog_load_opts *opts, long cookie);
+/* If auto-attach is not supported, callback should return 0 and set link to NULL */
+typedef int (*libbpf_prog_attach_fn_t)(const struct bpf_program *prog, long cookie,
+ struct bpf_link **link);
/* stored as sec_def->cookie for all libbpf-supported SEC()s */
enum sec_def_flags {
@@ -239,9 +240,9 @@ struct bpf_sec_def {
enum bpf_attach_type expected_attach_type;
long cookie;
- init_fn_t init_fn;
- preload_fn_t preload_fn;
- attach_fn_t attach_fn;
+ libbpf_prog_init_fn_t init_fn;
+ libbpf_prog_preload_fn_t preload_fn;
+ libbpf_prog_attach_fn_t attach_fn;
};
/*
@@ -8581,12 +8582,12 @@ int bpf_program__set_log_buf(struct bpf_program *prog, char *log_buf, size_t log
__VA_ARGS__ \
}
-static struct bpf_link *attach_kprobe(const struct bpf_program *prog, long cookie);
-static struct bpf_link *attach_tp(const struct bpf_program *prog, long cookie);
-static struct bpf_link *attach_raw_tp(const struct bpf_program *prog, long cookie);
-static struct bpf_link *attach_trace(const struct bpf_program *prog, long cookie);
-static struct bpf_link *attach_lsm(const struct bpf_program *prog, long cookie);
-static struct bpf_link *attach_iter(const struct bpf_program *prog, long cookie);
+static int attach_kprobe(const struct bpf_program *prog, long cookie, struct bpf_link **link);
+static int attach_tp(const struct bpf_program *prog, long cookie, struct bpf_link **link);
+static int attach_raw_tp(const struct bpf_program *prog, long cookie, struct bpf_link **link);
+static int attach_trace(const struct bpf_program *prog, long cookie, struct bpf_link **link);
+static int attach_lsm(const struct bpf_program *prog, long cookie, struct bpf_link **link);
+static int attach_iter(const struct bpf_program *prog, long cookie, struct bpf_link **link);
static const struct bpf_sec_def section_defs[] = {
SEC_DEF("socket", SOCKET_FILTER, 0, SEC_NONE | SEC_SLOPPY_PFX),
@@ -10093,14 +10094,13 @@ struct bpf_link *bpf_program__attach_kprobe(const struct bpf_program *prog,
return bpf_program__attach_kprobe_opts(prog, func_name, &opts);
}
-static struct bpf_link *attach_kprobe(const struct bpf_program *prog, long cookie)
+static int attach_kprobe(const struct bpf_program *prog, long cookie, struct bpf_link **link)
{
DECLARE_LIBBPF_OPTS(bpf_kprobe_opts, opts);
unsigned long offset = 0;
- struct bpf_link *link;
const char *func_name;
char *func;
- int n, err;
+ int n;
opts.retprobe = str_has_pfx(prog->sec_name, "kretprobe/");
if (opts.retprobe)
@@ -10110,21 +10110,19 @@ static struct bpf_link *attach_kprobe(const struct bpf_program *prog, long cooki
n = sscanf(func_name, "%m[a-zA-Z0-9_.]+%li", &func, &offset);
if (n < 1) {
- err = -EINVAL;
pr_warn("kprobe name is invalid: %s\n", func_name);
- return libbpf_err_ptr(err);
+ return -EINVAL;
}
if (opts.retprobe && offset != 0) {
free(func);
- err = -EINVAL;
pr_warn("kretprobes do not support offset specification\n");
- return libbpf_err_ptr(err);
+ return -EINVAL;
}
opts.offset = offset;
- link = bpf_program__attach_kprobe_opts(prog, func, &opts);
+ *link = bpf_program__attach_kprobe_opts(prog, func, &opts);
free(func);
- return link;
+ return libbpf_get_error(*link);
}
static void gen_uprobe_legacy_event_name(char *buf, size_t buf_sz,
@@ -10379,14 +10377,13 @@ struct bpf_link *bpf_program__attach_tracepoint(const struct bpf_program *prog,
return bpf_program__attach_tracepoint_opts(prog, tp_category, tp_name, NULL);
}
-static struct bpf_link *attach_tp(const struct bpf_program *prog, long cookie)
+static int attach_tp(const struct bpf_program *prog, long cookie, struct bpf_link **link)
{
char *sec_name, *tp_cat, *tp_name;
- struct bpf_link *link;
sec_name = strdup(prog->sec_name);
if (!sec_name)
- return libbpf_err_ptr(-ENOMEM);
+ return -ENOMEM;
/* extract "tp/<category>/<name>" or "tracepoint/<category>/<name>" */
if (str_has_pfx(prog->sec_name, "tp/"))
@@ -10396,14 +10393,14 @@ static struct bpf_link *attach_tp(const struct bpf_program *prog, long cookie)
tp_name = strchr(tp_cat, '/');
if (!tp_name) {
free(sec_name);
- return libbpf_err_ptr(-EINVAL);
+ return -EINVAL;
}
*tp_name = '\0';
tp_name++;
- link = bpf_program__attach_tracepoint(prog, tp_cat, tp_name);
+ *link = bpf_program__attach_tracepoint(prog, tp_cat, tp_name);
free(sec_name);
- return link;
+ return libbpf_get_error(*link);
}
struct bpf_link *bpf_program__attach_raw_tracepoint(const struct bpf_program *prog,
@@ -10436,7 +10433,7 @@ struct bpf_link *bpf_program__attach_raw_tracepoint(const struct bpf_program *pr
return link;
}
-static struct bpf_link *attach_raw_tp(const struct bpf_program *prog, long cookie)
+static int attach_raw_tp(const struct bpf_program *prog, long cookie, struct bpf_link **link)
{
static const char *const prefixes[] = {
"raw_tp/",
@@ -10456,10 +10453,11 @@ static struct bpf_link *attach_raw_tp(const struct bpf_program *prog, long cooki
if (!tp_name) {
pr_warn("prog '%s': invalid section name '%s'\n",
prog->name, prog->sec_name);
- return libbpf_err_ptr(-EINVAL);
+ return -EINVAL;
}
- return bpf_program__attach_raw_tracepoint(prog, tp_name);
+ *link = bpf_program__attach_raw_tracepoint(prog, tp_name);
+ return libbpf_get_error(link);
}
/* Common logic for all BPF program types that attach to a btf_id */
@@ -10502,14 +10500,16 @@ struct bpf_link *bpf_program__attach_lsm(const struct bpf_program *prog)
return bpf_program__attach_btf_id(prog);
}
-static struct bpf_link *attach_trace(const struct bpf_program *prog, long cookie)
+static int attach_trace(const struct bpf_program *prog, long cookie, struct bpf_link **link)
{
- return bpf_program__attach_trace(prog);
+ *link = bpf_program__attach_trace(prog);
+ return libbpf_get_error(*link);
}
-static struct bpf_link *attach_lsm(const struct bpf_program *prog, long cookie)
+static int attach_lsm(const struct bpf_program *prog, long cookie, struct bpf_link **link)
{
- return bpf_program__attach_lsm(prog);
+ *link = bpf_program__attach_lsm(prog);
+ return libbpf_get_error(*link);
}
static struct bpf_link *
@@ -10638,17 +10638,33 @@ bpf_program__attach_iter(const struct bpf_program *prog,
return link;
}
-static struct bpf_link *attach_iter(const struct bpf_program *prog, long cookie)
+static int attach_iter(const struct bpf_program *prog, long cookie, struct bpf_link **link)
{
- return bpf_program__attach_iter(prog, NULL);
+ *link = bpf_program__attach_iter(prog, NULL);
+ return libbpf_get_error(*link);
}
struct bpf_link *bpf_program__attach(const struct bpf_program *prog)
{
+ struct bpf_link *link = NULL;
+ int err;
+
if (!prog->sec_def || !prog->sec_def->attach_fn)
- return libbpf_err_ptr(-ESRCH);
+ return libbpf_err_ptr(-EOPNOTSUPP);
- return prog->sec_def->attach_fn(prog, prog->sec_def->cookie);
+ err = prog->sec_def->attach_fn(prog, prog->sec_def->cookie, &link);
+ if (err)
+ return libbpf_err_ptr(err);
+
+ /* When calling bpf_program__attach() explicitly, auto-attach support
+ * is expected to work, so NULL returned link is considered an error.
+ * This is different for skeleton's attach, see comment in
+ * bpf_object__attach_skeleton().
+ */
+ if (!link)
+ return libbpf_err_ptr(-EOPNOTSUPP);
+
+ return link;
}
static int bpf_link__detach_struct_ops(struct bpf_link *link)
@@ -11792,13 +11808,27 @@ int bpf_object__attach_skeleton(struct bpf_object_skeleton *s)
if (!prog->sec_def || !prog->sec_def->attach_fn)
continue;
- *link = bpf_program__attach(prog);
- err = libbpf_get_error(*link);
+ /* if user already set the link manually, don't attempt auto-attach */
+ if (*link)
+ continue;
+
+ err = prog->sec_def->attach_fn(prog, prog->sec_def->cookie, link);
if (err) {
- pr_warn("failed to auto-attach program '%s': %d\n",
+ pr_warn("prog '%s': failed to auto-attach: %d\n",
bpf_program__name(prog), err);
return libbpf_err(err);
}
+
+ /* It's possible that for some SEC() definitions auto-attach
+ * is supported in some cases (e.g., if definition completely
+ * specifies target information), but is not in other cases.
+ * SEC("uprobe") is one such case. If user specified target
+ * binary and function name, such BPF program can be
+ * auto-attached. But if not, it shouldn't trigger skeleton's
+ * attach to fail. It should just be skipped.
+ * attach_fn signals such case with returning 0 (no error) and
+ * setting link to NULL.
+ */
}
return 0;
--
2.30.2
