[PATCHv3,0/9] bpf: Add d_path helper

hi,
adding d_path helper to return full path for 'path' object.

I originally added and used 'file_path' helper, which did the same,
but used 'struct file' object. Then realized that file_path is just
a wrapper for d_path, so we'd cover more calling sites if we add
d_path helper and allowed resolving BTF object within another object,
so we could call d_path also with file pointer, like:

  bpf_d_path(&file->f_path, buf, size);

This feature is mainly to be able to add dpath (filepath originally)
function to bpftrace:

  # bpftrace -e 'kfunc:vfs_open { printf("%s\n", dpath(args->path)); }'

v3 changes:
  - changed tests to use seleton and vmlinux.h [Andrii]
  - refactored to define ID lists in C object [Andrii]
  - changed btf_struct_access for nested ID check,
    instead of adding new function for that [Andrii]
  - fail build with CONFIG_DEBUG_INFO_BTF if libelf is not detected [Andrii]

Also available at:
  https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
  bpf/d_path

thanks,
jirka


---
Jiri Olsa (11):
      bpf: Add btfid tool to resolve BTF IDs in ELF object
      bpf: Compile btfid tool at kernel compilation start
      bpf: Add btf_ids object
      bpf: Resolve BTF IDs in vmlinux image
      bpf: Remove btf_id helpers resolving
      bpf: Do not pass enum bpf_access_type to btf_struct_access
      bpf: Allow nested BTF object to be refferenced by BTF object + offset
      bpf: Add BTF whitelist support
      bpf: Add d_path helper
      selftests/bpf: Add verifier test for d_path helper
      selftests/bpf: Add test for d_path helper

 Makefile                                        |  25 ++++-
 include/asm-generic/vmlinux.lds.h               |   4 +
 include/linux/bpf.h                             |  16 ++-
 include/uapi/linux/bpf.h                        |  14 ++-
 kernel/bpf/Makefile                             |   2 +-
 kernel/bpf/btf.c                                | 149 +++++++++++--------------
 kernel/bpf/btf_ids.c                            |  26 +++++
 kernel/bpf/btf_ids.h                            | 108 ++++++++++++++++++
 kernel/bpf/verifier.c                           |  39 +++++--
 kernel/trace/bpf_trace.c                        |  40 ++++++-
 net/core/filter.c                               |   2 -
 net/ipv4/bpf_tcp_ca.c                           |   2 +-
 scripts/bpf_helpers_doc.py                      |   2 +
 scripts/link-vmlinux.sh                         |   6 +
 tools/Makefile                                  |   3 +
 tools/bpf/Makefile                              |   5 +-
 tools/bpf/btfid/Build                           |  26 +++++
 tools/bpf/btfid/Makefile                        |  71 ++++++++++++
 tools/bpf/btfid/btfid.c                         | 627 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 tools/include/uapi/linux/bpf.h                  |  14 ++-
 tools/testing/selftests/bpf/prog_tests/d_path.c | 153 +++++++++++++++++++++++++
 tools/testing/selftests/bpf/progs/test_d_path.c |  55 +++++++++
 tools/testing/selftests/bpf/test_verifier.c     |  13 ++-
 tools/testing/selftests/bpf/verifier/d_path.c   |  38 +++++++
 24 files changed, 1329 insertions(+), 111 deletions(-)
 create mode 100644 kernel/bpf/btf_ids.c
 create mode 100644 kernel/bpf/btf_ids.h
 create mode 100644 tools/bpf/btfid/Build
 create mode 100644 tools/bpf/btfid/Makefile
 create mode 100644 tools/bpf/btfid/btfid.c
 create mode 100644 tools/testing/selftests/bpf/prog_tests/d_path.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_d_path.c
 create mode 100644 tools/testing/selftests/bpf/verifier/d_path.c

Jiri Olsa wrote:
> hi,
> adding d_path helper to return full path for 'path' object.
> 
> I originally added and used 'file_path' helper, which did the same,
> but used 'struct file' object. Then realized that file_path is just
> a wrapper for d_path, so we'd cover more calling sites if we add
> d_path helper and allowed resolving BTF object within another object,
> so we could call d_path also with file pointer, like:
> 
>   bpf_d_path(&file->f_path, buf, size);
> 
> This feature is mainly to be able to add dpath (filepath originally)
> function to bpftrace:
> 
>   # bpftrace -e 'kfunc:vfs_open { printf("%s\n", dpath(args->path)); }'
> 
> v3 changes:
>   - changed tests to use seleton and vmlinux.h [Andrii]
>   - refactored to define ID lists in C object [Andrii]
>   - changed btf_struct_access for nested ID check,
>     instead of adding new function for that [Andrii]
>   - fail build with CONFIG_DEBUG_INFO_BTF if libelf is not detected [Andrii]
> 
> Also available at:
>   https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
>   bpf/d_path
> 
> thanks,
> jirka

Hi Jira, Apologize for waiting until v3 to look at this series, but a
couple general requests as I review this.

In the cover letter can we get some more details. The above is really
terse/cryptic in my opinion. The bpftrace example gives good motiviation,
but nothing above mentions a new .BTF_ids section and the flow to create
and use this section.

Also if we add a BTF_ids  section adding documentation in btf.rst should
happen as well. I would like to see something in the ELF File Format
Interface section and BTF Generation sections.

I'm not going to nitpick if its in this series or a stand-alone patch
but do want to see it. So far the Documentation on BTF is fairly
good and I want to avoid these kind of gaps.

Thanks!
John

On Thu, Jun 18, 2020 at 01:57:19PM -0700, John Fastabend wrote:
> Jiri Olsa wrote:
> > hi,
> > adding d_path helper to return full path for 'path' object.
> > 
> > I originally added and used 'file_path' helper, which did the same,
> > but used 'struct file' object. Then realized that file_path is just
> > a wrapper for d_path, so we'd cover more calling sites if we add
> > d_path helper and allowed resolving BTF object within another object,
> > so we could call d_path also with file pointer, like:
> > 
> >   bpf_d_path(&file->f_path, buf, size);
> > 
> > This feature is mainly to be able to add dpath (filepath originally)
> > function to bpftrace:
> > 
> >   # bpftrace -e 'kfunc:vfs_open { printf("%s\n", dpath(args->path)); }'
> > 
> > v3 changes:
> >   - changed tests to use seleton and vmlinux.h [Andrii]
> >   - refactored to define ID lists in C object [Andrii]
> >   - changed btf_struct_access for nested ID check,
> >     instead of adding new function for that [Andrii]
> >   - fail build with CONFIG_DEBUG_INFO_BTF if libelf is not detected [Andrii]
> > 
> > Also available at:
> >   https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
> >   bpf/d_path
> > 
> > thanks,
> > jirka
> 
> Hi Jira, Apologize for waiting until v3 to look at this series, but a
> couple general requests as I review this.
> 
> In the cover letter can we get some more details. The above is really
> terse/cryptic in my opinion. The bpftrace example gives good motiviation,
> but nothing above mentions a new .BTF_ids section and the flow to create
> and use this section.

ok, will add more details in next version

> 
> Also if we add a BTF_ids  section adding documentation in btf.rst should
> happen as well. I would like to see something in the ELF File Format
> Interface section and BTF Generation sections.

did not know there was bpf.rst ;-) will update

> 
> I'm not going to nitpick if its in this series or a stand-alone patch
> but do want to see it. So far the Documentation on BTF is fairly
> good and I want to avoid these kind of gaps.

sure, thanks

jirka

> 
> Thanks!
> John
>