From fc00c656c96528112d05cf0edf8631bd5eaea446 Mon Sep 17 00:00:00 2001
From: Kacper <kacper@mail.openlinux.dev>
Date: Sun, 7 Dec 2025 20:10:31 +0100
Subject: Add build system scaffolding and libc headers

---
 lib/libc/grp/getgrgid.c   | 15 ++++++++++
 lib/libc/grp/getgrgid_r.c | 74 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 89 insertions(+)
 create mode 100644 lib/libc/grp/getgrgid.c
 create mode 100644 lib/libc/grp/getgrgid_r.c

(limited to 'lib/libc/grp')

diff --git a/lib/libc/grp/getgrgid.c b/lib/libc/grp/getgrgid.c
new file mode 100644
index 00000000..66ccaff1
--- /dev/null
+++ b/lib/libc/grp/getgrgid.c
@@ -0,0 +1,15 @@
+#include <grp.h>
+#include <stddef.h>
+#include <limits.h>
+
+struct group *getgrgid(gid_t gid)
+{
+	static struct group grp;
+	static char buf[LINE_MAX * 2];
+	struct group *res;
+
+	if (getgrgid_r(gid, &grp, buf, sizeof(buf), &res) != 0)
+		return NULL;
+
+	return res;
+}
diff --git a/lib/libc/grp/getgrgid_r.c b/lib/libc/grp/getgrgid_r.c
new file mode 100644
index 00000000..b3449d14
--- /dev/null
+++ b/lib/libc/grp/getgrgid_r.c
@@ -0,0 +1,74 @@
+#include <grp.h>
+#include <string.h>
+#include <limits.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+int getgrgid_r(gid_t gid, struct group *grp, char *buf, size_t buflen,
+	       struct group **result)
+{
+	FILE *f = fopen("/etc/group", "r");
+	if (!f) {
+		*result = NULL;
+		return errno;
+	}
+
+	char line[LINE_MAX];
+	char *members[1024];
+
+	while (fgets(line, sizeof(line), f)) {
+		char *name = strtok(line, ":");
+		char *passwd = strtok(NULL, ":");
+		char *gid_str = strtok(NULL, ":");
+		char *mem_str = strtok(NULL, "\n");
+
+		if (!name || !passwd || !gid_str)
+			continue;
+
+		gid_t file_gid = (gid_t)strtoul(gid_str, NULL, 10);
+		if (file_gid != gid)
+			continue;
+
+		size_t len = strlen(name) + 1;
+		if (len > buflen) {
+			fclose(f);
+			*result = NULL;
+			return ERANGE;
+		}
+		memcpy(buf, name, len);
+		grp->gr_name = buf;
+		buf += len;
+		buflen -= len;
+
+		grp->gr_gid = file_gid;
+
+		int i = 0;
+		if (mem_str && *mem_str) {
+			char *tok = strtok(mem_str, ",");
+			while (tok && i < 1023) {
+				size_t l = strlen(tok) + 1;
+				if (l > buflen) {
+					fclose(f);
+					*result = NULL;
+					return ERANGE;
+				}
+				memcpy(buf, tok, l);
+				members[i++] = buf;
+				buf += l;
+				buflen -= l;
+				tok = strtok(NULL, ",");
+			}
+		}
+		members[i] = NULL;
+		grp->gr_mem = members;
+
+		fclose(f);
+		*result = grp;
+		return 0;
+	}
+
+	fclose(f);
+	*result = NULL;
+	return 0;
+}
-- 
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