Hi,
在 2022/4/5 06:17, Andrii Nakryiko 写道:
On Thu, Mar 31, 2022 at 6:34 PM Song Chen <chensong_2000@xxxxxx> wrote:
When i was writing my eBPF program, i copied some pieces of code from
syscall_tp, syscall_tp_kern only records how many files are opened, but
mine needs to print file name.I reused struct syscalls_enter_open_args,
which is defined as:
struct syscalls_enter_open_args {
unsigned long long unused;
long syscall_nr;
long filename_ptr;
long flags;
long mode;
};
I tried to use filename_ptr, but it's not the pointer of filename, flags
turns out to be the pointer I'm looking for, there might be something
missed in the struct.
I read the ftrace log, found the missed one is dfd, which is supposed to be
placed in between syscall_nr and filename_ptr.
Actually syscall_tp has nothing to do with dfd, it can run anyway without
it, but it's better to have it to make it a better eBPF sample, especially
to new eBPF programmers, then i fixed it.
Signed-off-by: Song Chen <chensong_2000@xxxxxx>
---
samples/bpf/syscall_tp_kern.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/samples/bpf/syscall_tp_kern.c b/samples/bpf/syscall_tp_kern.c
index 50231c2eff9c..e4ac818aee57 100644
--- a/samples/bpf/syscall_tp_kern.c
+++ b/samples/bpf/syscall_tp_kern.c
@@ -7,6 +7,7 @@
struct syscalls_enter_open_args {
unsigned long long unused;
long syscall_nr;
+ long dfd_ptr;
long filename_ptr;
long flags;
long mode;
Here's what I see on latest bpf-next:
# cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_open/format
name: sys_enter_open
ID: 613
format:
field:unsigned short common_type; offset:0;
size:2; signed:0;
field:unsigned char common_flags; offset:2;
size:1; signed:0;
field:unsigned char common_preempt_count; offset:3;
size:1; signed:0;
field:int common_pid; offset:4; size:4; signed:1;
field:int __syscall_nr; offset:8; size:4; signed:1;
field:const char * filename; offset:16; size:8; signed:0;
field:int flags; offset:24; size:8; signed:0;
field:umode_t mode; offset:32; size:8; signed:0;
This layout doesn't correspond either to before or after state of
syscalls_enter_open_args. Not sure what's going on, but it doesn't
seem that struct syscalls_enter_open_args is correct anyways.
sys_enter_open is not enabled in my system somehow and i haven't figured
out why, then i used sys_enter_openat, whose format is:
name: sys_enter_openat
ID: 647
format:
field:unsigned short common_type; offset:0; size:2; signed:0;
field:unsigned char common_flags; offset:2; size:1; signed:0;
field:unsigned char common_preempt_count; offset:3; size:1; signed:0;
field:int common_pid; offset:4; size:4; signed:1;
field:int __syscall_nr; offset:8; size:4; signed:1;
field:int dfd; offset:16; size:8; signed:0;
field:const char * filename; offset:24; size:8; signed:0;
field:int flags; offset:32; size:8; signed:0;
field:umode_t mode; offset:40; size:8; signed:0;
print fmt: "dfd: 0x%08lx, filename: 0x%08lx, flags: 0x%08lx, mode:
0x%08lx", ((unsigned long)(REC->dfd)), ((unsigned long)(REC->filename)),
((unsigned long)(REC->flags)), ((unsigned long)(REC->mode))
I think in this case syscalls_enter_open_args is not applicable for
sys_enter_openat, how about we introduce a new struct specific for
sys_enter_openat with dfd in it?
/Song
--
2.25.1
