On Fri, Nov 1, 2019 at 5:57 AM Wenbo Zhang <ethercflow@xxxxxxxxx> wrote: > > When people want to identify which file system files are being opened, > read, and written to, they can use this helper with file descriptor as > input to achieve this goal. Other pseudo filesystems are also supported. > > This requirement is mainly discussed here: > > https://github.com/iovisor/bcc/issues/237 > > v4->v5: addressed Andrii and Daniel's feedback > - rename bpf_fd2path to bpf_get_file_path to be consistent with other > helper's names > - when fdget_raw fails, set ret to -EBADF instead of -EINVAL > - remove fdput from fdget_raw's error path > - use IS_ERR instead of IS_ERR_OR_NULL as d_path ether returns a pointer > into the buffer or an error code if the path was too long > - modify the normal path's return value to return copied string lengh > including NUL > - update this helper description's Return bits. > > v3->v4: addressed Daniel's feedback > - fix missing fdput() > - move fd2path from kernel/bpf/trace.c to kernel/trace/bpf_trace.c > - move fd2path's test code to another patch > - add comment to explain why use fdget_raw instead of fdget > > v2->v3: addressed Yonghong's feedback > - remove unnecessary LOCKDOWN_BPF_READ > - refactor error handling section for enhanced readability > - provide a test case in tools/testing/selftests/bpf > > v1->v2: addressed Daniel's feedback > - fix backward compatibility > - add this helper description > - fix signed-off name > --- See nit below, but I'm fine with the current state as well. Acked-by: Andrii Nakryiko <andriin@xxxxxx> > /* integer value in 'imm' field of BPF_CALL instruction selects which helper > * function eBPF program intends to call > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > index f50bf19f7a05..fc9f577e65f5 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -683,6 +683,53 @@ static const struct bpf_func_proto bpf_send_signal_proto = { > .arg1_type = ARG_ANYTHING, > }; > > +BPF_CALL_3(bpf_get_file_path, char *, dst, u32, size, int, fd) > +{ > + struct fd f; > + char *p; > + int ret = -EBADF; > + > + /* Use fdget_raw instead of fdget to support O_PATH, and > + * fdget_raw doesn't have any sleepable code, so it's ok > + * to be here. > + */ > + f = fdget_raw(fd); > + if (!f.file) > + goto error; > + > + /* d_path doesn't have any sleepable code, so it's ok to > + * be here. But it uses the current macro to get fs_struct > + * (current->fs). So this helper shouldn't be called in > + * interrupt context. > + */ > + p = d_path(&f.file->f_path, dst, size); > + if (IS_ERR(p)) { > + ret = PTR_ERR(p); > + fdput(f); > + goto error; > + } > + > + ret = strlen(p); > + memmove(dst, p, ret); > + dst[ret++] = '\0'; > + fdput(f); > + goto end; > + > +error: > + memset(dst, '0', size); > +end: > + return ret; nit: I'd avoid unnecessary goto end (and end label itself) by having two explicit returns: return 0; error: memset(...); return ret; > +} > + > +static const struct bpf_func_proto bpf_get_file_path_proto = { > + .func = bpf_get_file_path, > + .gpl_only = true, > + .ret_type = RET_INTEGER, > + .arg1_type = ARG_PTR_TO_UNINIT_MEM, > + .arg2_type = ARG_CONST_SIZE, > + .arg3_type = ARG_ANYTHING, > +}; > + > static const struct bpf_func_proto * > tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) > { > @@ -735,6 +782,8 @@ tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) > #endif > case BPF_FUNC_send_signal: > return &bpf_send_signal_proto; > + case BPF_FUNC_get_file_path: > + return &bpf_get_file_path_proto; This seems like a rather useful helper not just in tracing context. So if maintainers are ok with that, maybe you can follow up with patch that adds it in more BPF program types. > default: > return NULL; > } [...]
