Re: [PATCH bpf-next] bpf: Introduce bpf generic log
From: Leon Hwang
Date: Thu Jul 06 2023 - 05:36:44 EST
On 6/7/23 00:54, Daniel Borkmann wrote:
On 7/5/23 6:20 PM, Leon Hwang wrote:
On 2023/7/5 22:39, Daniel Borkmann wrote:
On 7/5/23 3:20 PM, Leon Hwang wrote:
Currently, excluding verifier, users are unable to obtain detailed
error
information when issues occur in BPF syscall.
To overcome this limitation, bpf generic log is introduced to provide
error details similar to the verifier. This enhancement will enable
the
reporting of error details along with the corresponding errno in BPF
syscall.
Essentially, bpf generic log functions as a mechanism similar to
netlink,
enabling the transmission of error messages to user space. This
mechanism greatly enhances the usability of BPF syscall by allowing
users to access comprehensive error messages instead of relying solely
on errno.
This patch specifically addresses the error reporting in
dev_xdp_attach()
. With this patch, the error messages will be transferred to user
space
like the netlink approach. Hence, users will be able to check the
error
message along with the errno.
Signed-off-by: Leon Hwang <hffilwlqm@xxxxxxxxx>
---
include/linux/bpf.h | 30 ++++++++++++++++++++++++++++++
include/uapi/linux/bpf.h | 6 ++++++
kernel/bpf/log.c | 33
+++++++++++++++++++++++++++++++++
net/core/dev.c | 11 ++++++++++-
tools/include/uapi/linux/bpf.h | 6 ++++++
5 files changed, 85 insertions(+), 1 deletion(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index f58895830..fd63f4a76 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -3077,4 +3077,34 @@ static inline gfp_t bpf_memcg_flags(gfp_t
flags)
return flags;
}
+#define BPF_GENERIC_TMP_LOG_SIZE 256
+
+struct bpf_generic_log {
+ char kbuf[BPF_GENERIC_TMP_LOG_SIZE];
+ char __user *ubuf;
+ u32 len_used;
+ u32 len_total;
+};
+
+__printf(2, 3) void bpf_generic_log_write(struct bpf_generic_log
*log,
+ const char *fmt, ...);
+static inline void bpf_generic_log_init(struct bpf_generic_log *log,
+ const struct bpf_generic_user_log *ulog)
+{
+ log->ubuf = (char __user *) (unsigned long) ulog->log_buf;
+ log->len_total = ulog->log_size;
+ log->len_used = 0;
+}
+
+#define BPF_GENERIC_LOG_WRITE(log, ulog, fmt, ...) do { \
+ const char *____fmt = (fmt); \
+ bpf_generic_log_init(log, ulog); \
+ bpf_generic_log_write(log, ____fmt, ##__VA_ARGS__); \
+} while (0)
+
+#define BPF_GENERIC_ULOG_WRITE(ulog, fmt, ...) do { \
+ struct bpf_generic_log ____log; \
+ BPF_GENERIC_LOG_WRITE(&____log, ulog, fmt, ##__VA_ARGS__); \
+} while (0)
+
Could we generalize the bpf_verifier_log infra and reuse bpf_log()
helper
instead of adding something new?
Yes. It's possible to reuse the bpf_verifier_log infra and reuse
bpf_log()
helper. I'll try this way:
#define BPF_LOG_USER BPF_LOG_LEVEL1 /* user log flag */
#define BPF_ULOG_WRITE(log_buf, log_size, fmt, ...) do { \
const char *____fmt =
(fmt); \
struct bpf_verifier_log
____vlog; \
bpf_vlog_init(&____vlog, BPF_LOG_USER, log_buf,
log_size); \
bpf_log(&____vlog, ____fmt,
##__VA_ARGS__); \
} while (0)
Could we hide all of this inside bpf_log() or better create a new
bpf_log_once() wrapper,
passing in attr so we only need to use the latter w/o the extra macros?
Essentially what your bpf_xdp_link_log() is doing, just that
bpf_log_once(attr, extack._msg)
would be generic and sufficient.
Thanks,
Daniel
I try to use BPF_ULOG_WRITE() successfully, but with a warning:
net/core/dev.c: In function 'bpf_xdp_link_log.isra.0':
net/core/dev.c:9093:1: warning: the frame size of 1056 bytes is larger
than 1024 bytes [-Wframe-larger-than=]
9093 | }
|
How should we generalize the bpf_verifier_log infra with a smaller
BPF_VERIFIER_TMP_LOG_SIZE (1024 currently) ?
If to use bpf_log_once(attr, extack._msg), I think
bpf_ulog_once(&attr->link_create.xdp.log, extack._msg)
is better. attr->link_create.xdp.log is struct bpf_generic_user_log.
Or bpf_xdp_link_log() is better to wrap log details.