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

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 <redacted>
Signed-off-by: Rafael David Tinoco <redacted>
Signed-off-by: Lorenzo Fontana <redacted>
Signed-off-by: Leonardo Di Donato <redacted>
---
 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"

                "       %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;

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

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

+
+       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;