Re: [PATCH bpf-next v5 2/9] bpftool: Add gen min_core_btf command

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Fri, Jan 28, 2022 at 2:33 PM Mauricio Vásquez <mauricio@kinvolk.io> wrote:
>
> This command is implemented under the "gen" command in bpftool and the
> syntax is the following:
>
> $ bpftool gen min_core_btf INPUT OUTPUT OBJECT(S)
>
> INPUT can be either a single BTF file or a folder containing BTF files,
> when it's a folder, a BTF file is generated for each BTF file contained
> in this folder. OUTPUT is the file (or folder) where generated files are
> stored and OBJECT(S) is the list of bpf objects we want to generate the
> BTF file(s) for (each generated BTF file contains all the types needed
> by all the objects).
>
> Signed-off-by: Mauricio Vásquez <mauricio@kinvolk.io>
> Signed-off-by: Rafael David Tinoco <rafael.tinoco@aquasec.com>
> Signed-off-by: Lorenzo Fontana <lorenzo.fontana@elastic.co>
> Signed-off-by: Leonardo Di Donato <leonardo.didonato@elastic.co>
> ---
>  tools/bpf/bpftool/bash-completion/bpftool |   6 +-
>  tools/bpf/bpftool/gen.c                   | 112 +++++++++++++++++++++-
>  2 files changed, 114 insertions(+), 4 deletions(-)
>
> diff --git a/tools/bpf/bpftool/bash-completion/bpftool b/tools/bpf/bpftool/bash-completion/bpftool
> index 493753a4962e..958e1fd71b5c 100644
> --- a/tools/bpf/bpftool/bash-completion/bpftool
> +++ b/tools/bpf/bpftool/bash-completion/bpftool
> @@ -1003,9 +1003,13 @@ _bpftool()
>                              ;;
>                      esac
>                      ;;
> +                min_core_btf)
> +                    _filedir
> +                    return 0
> +                    ;;
>                  *)
>                      [[ $prev == $object ]] && \
> -                        COMPREPLY=( $( compgen -W 'object skeleton help' -- "$cur" ) )
> +                        COMPREPLY=( $( compgen -W 'object skeleton help min_core_btf' -- "$cur" ) )
>                      ;;
>              esac
>              ;;
> diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
> index 8f78c27d41f0..7db31b0f265f 100644
> --- a/tools/bpf/bpftool/gen.c
> +++ b/tools/bpf/bpftool/gen.c
> @@ -5,6 +5,7 @@
>  #define _GNU_SOURCE
>  #endif
>  #include <ctype.h>
> +#include <dirent.h>
>  #include <errno.h>
>  #include <fcntl.h>
>  #include <linux/err.h>
> @@ -1084,6 +1085,7 @@ static int do_help(int argc, char **argv)
>         fprintf(stderr,
>                 "Usage: %1$s %2$s object OUTPUT_FILE INPUT_FILE [INPUT_FILE...]\n"
>                 "       %1$s %2$s skeleton FILE [name OBJECT_NAME]\n"
> +               "       %1$s %2$s min_core_btf INPUT OUTPUT OBJECT(S)\n"

OBJECTS(S) should be OBJECT... for this "CLI notation", no?

>                 "       %1$s %2$s help\n"
>                 "\n"
>                 "       " HELP_SPEC_OPTIONS " |\n"
> @@ -1094,10 +1096,114 @@ static int do_help(int argc, char **argv)
>         return 0;
>  }
>
> +/* Create BTF file for a set of BPF objects */
> +static int btfgen(const char *src_btf, const char *dst_btf, const char *objspaths[])
> +{
> +       return -EOPNOTSUPP;
> +}
> +
> +static int do_min_core_btf(int argc, char **argv)
> +{
> +       char src_btf_path[PATH_MAX], dst_btf_path[PATH_MAX];
> +       bool input_is_file, output_is_file = true;
> +       const char *input, *output;
> +       const char **objs = NULL;
> +       struct dirent *dir;
> +       struct stat st;
> +       DIR *d = NULL;
> +       int i, err;
> +
> +       if (!REQ_ARGS(3)) {
> +               usage();
> +               return -1;
> +       }
> +
> +       input = GET_ARG();
> +       if (stat(input, &st) < 0) {
> +               p_err("failed to stat %s: %s", input, strerror(errno));
> +               return -errno;
> +       }
> +
> +       if ((st.st_mode & S_IFMT) != S_IFDIR && (st.st_mode & S_IFMT) != S_IFREG) {
> +               p_err("file type not valid: %s", input);
> +               return -EINVAL;
> +       }
> +
> +       input_is_file = (st.st_mode & S_IFMT) == S_IFREG;

move before if and use input_is_file in the if itself instead of
duplicating all the S_IFREG flags?

> +
> +       output = GET_ARG();
> +       if (stat(output, &st) == 0 && (st.st_mode & S_IFMT) == S_IFDIR)
> +               output_is_file = false;

if stat() succeeds but it's neither directory or file, should be an
error, right?

> +
> +       objs = (const char **) malloc((argc + 1) * sizeof(*objs));

calloc() seems to be better suited for this (and zero-intialization is
nice for safety and to avoid objs[argc] = NULL after the loop below)

> +       if (!objs) {
> +               p_err("failed to allocate array for object names");
> +               return -ENOMEM;
> +       }
> +
> +       i = 0;
> +       while (argc > 0)
> +               objs[i++] = GET_ARG();

for (i = 0; i < argc; i++) ?

> +
> +       objs[i] = NULL;
> +
> +       /* single BTF file */
> +       if (input_is_file) {
> +               p_info("Processing source BTF file: %s", input);
> +
> +               if (output_is_file) {
> +                       err = btfgen(input, output, objs);
> +                       goto out;
> +               }
> +               snprintf(dst_btf_path, sizeof(dst_btf_path), "%s/%s", output,
> +                        basename(input));
> +               err = btfgen(input, dst_btf_path, objs);
> +               goto out;
> +       }
> +
> +       if (output_is_file) {
> +               p_err("can't have just one file as output");
> +               err = -EINVAL;
> +               goto out;
> +       }
> +
> +       /* directory with BTF files */
> +       d = opendir(input);
> +       if (!d) {
> +               p_err("error opening input dir: %s", strerror(errno));
> +               err = -errno;
> +               goto out;
> +       }
> +
> +       while ((dir = readdir(d)) != NULL) {
> +               if (dir->d_type != DT_REG)
> +                       continue;
> +
> +               if (strncmp(dir->d_name + strlen(dir->d_name) - 4, ".btf", 4))
> +                       continue;

this whole handling of input directory feels a bit icky, tbh... maybe
we should require explicit listing of input files always. In CLI
invocation those could be separated by "keywords", something like
this:

bpftool gen min_core_btf <output> inputs <file1> <file2> .... objects
<obj1> <obj2> ...

a bit of a downside is that you can't have a file named "inputs" or
"objects", but that seems extremely unlikely? Quentin, any opinion as
well?

I'm mainly off put by a bit random ".btf" naming convention, the
DT_REG skipping, etc.

Another cleaner alternative from POV of bpftool (but might be less
convenient for users) is to use @file convention to specify a file
that contains a list of files. So

bpftool gen min_core_btf <output> @btf_filelist.txt @obj_filelist.txt

would take lists of inputs and outputs from respective files?


But actually, let's take a step back again. Why should there be
multiple inputs and outputs? I can see why multiple objects are
mandatory (you have an application that has multiple BPF objects used
internally). But processing single vmlinux BTF at a time seems
absolutely fine. I don't buy that CO-RE relo processing is that slow
to require optimized batch processing.

I might have asked this before, sorry, but the duration between each
iteration of btfgen is pretty long and I'm losing the context.

> +
> +               snprintf(src_btf_path, sizeof(src_btf_path), "%s%s", input, dir->d_name);
> +               snprintf(dst_btf_path, sizeof(dst_btf_path), "%s%s", output, dir->d_name);
> +
> +               p_info("Processing source BTF file: %s", src_btf_path);
> +
> +               err = btfgen(src_btf_path, dst_btf_path, objs);
> +               if (err)
> +                       goto out;
> +       }
> +
> +out:
> +       free(objs);
> +       if (d)
> +               closedir(d);
> +       return err;
> +}
> +
>  static const struct cmd cmds[] = {
> -       { "object",     do_object },
> -       { "skeleton",   do_skeleton },
> -       { "help",       do_help },
> +       { "object",             do_object },
> +       { "skeleton",           do_skeleton },
> +       { "min_core_btf",       do_min_core_btf},
> +       { "help",               do_help },
>         { 0 }
>  };
>
> --
> 2.25.1
>