libbpf: Introduce errstr() for stringifying errno

Add function errstr(int err) that allows converting numeric error codes
into string representations.

Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20241111212919.368971-2-mykyta.yatsenko5@gmail.com

Author: mykyta5

tools/lib/bpf/str_error.c

@@ -5,6 +5,10 @@
 #include <errno.h>
 #include "str_error.h"
 
+#ifndef ENOTSUPP
+#define ENOTSUPP	524
+#endif
+
 /* make sure libbpf doesn't use kernel-only integer typedefs */
 #pragma GCC poison u8 u16 u32 u64 s8 s16 s32 s64
 
@@ -31,3 +35,70 @@ char *libbpf_strerror_r(int err, char *dst, int len)
 	}
 	return dst;
 }
+
+const char *errstr(int err)
+{
+	static __thread char buf[12];
+
+	if (err > 0)
+		err = -err;
+
+	switch (err) {
+	case -E2BIG:		return "-E2BIG";
+	case -EACCES:		return "-EACCES";
+	case -EADDRINUSE:	return "-EADDRINUSE";
+	case -EADDRNOTAVAIL:	return "-EADDRNOTAVAIL";
+	case -EAGAIN:		return "-EAGAIN";
+	case -EALREADY:		return "-EALREADY";
+	case -EBADF:		return "-EBADF";
+	case -EBADFD:		return "-EBADFD";
+	case -EBUSY:		return "-EBUSY";
+	case -ECANCELED:	return "-ECANCELED";
+	case -ECHILD:		return "-ECHILD";
+	case -EDEADLK:		return "-EDEADLK";
+	case -EDOM:		return "-EDOM";
+	case -EEXIST:		return "-EEXIST";
+	case -EFAULT:		return "-EFAULT";
+	case -EFBIG:		return "-EFBIG";
+	case -EILSEQ:		return "-EILSEQ";
+	case -EINPROGRESS:	return "-EINPROGRESS";
+	case -EINTR:		return "-EINTR";
+	case -EINVAL:		return "-EINVAL";
+	case -EIO:		return "-EIO";
+	case -EISDIR:		return "-EISDIR";
+	case -ELOOP:		return "-ELOOP";
+	case -EMFILE:		return "-EMFILE";
+	case -EMLINK:		return "-EMLINK";
+	case -EMSGSIZE:		return "-EMSGSIZE";
+	case -ENAMETOOLONG:	return "-ENAMETOOLONG";
+	case -ENFILE:		return "-ENFILE";
+	case -ENODATA:		return "-ENODATA";
+	case -ENODEV:		return "-ENODEV";
+	case -ENOENT:		return "-ENOENT";
+	case -ENOEXEC:		return "-ENOEXEC";
+	case -ENOLINK:		return "-ENOLINK";
+	case -ENOMEM:		return "-ENOMEM";
+	case -ENOSPC:		return "-ENOSPC";
+	case -ENOTBLK:		return "-ENOTBLK";
+	case -ENOTDIR:		return "-ENOTDIR";
+	case -ENOTSUPP:		return "-ENOTSUPP";
+	case -ENOTTY:		return "-ENOTTY";
+	case -ENXIO:		return "-ENXIO";
+	case -EOPNOTSUPP:	return "-EOPNOTSUPP";
+	case -EOVERFLOW:	return "-EOVERFLOW";
+	case -EPERM:		return "-EPERM";
+	case -EPIPE:		return "-EPIPE";
+	case -EPROTO:		return "-EPROTO";
+	case -EPROTONOSUPPORT:	return "-EPROTONOSUPPORT";
+	case -ERANGE:		return "-ERANGE";
+	case -EROFS:		return "-EROFS";
+	case -ESPIPE:		return "-ESPIPE";
+	case -ESRCH:		return "-ESRCH";
+	case -ETXTBSY:		return "-ETXTBSY";
+	case -EUCLEAN:		return "-EUCLEAN";
+	case -EXDEV:		return "-EXDEV";
+	default:
+		snprintf(buf, sizeof(buf), "%d", err);
+		return buf;
+	}
+}

tools/lib/bpf/str_error.h

@@ -6,4 +6,11 @@
 
 char *libbpf_strerror_r(int err, char *dst, int len);
 
+/**
+ * @brief **errstr()** returns string corresponding to numeric errno
+ * @param err negative numeric errno
+ * @return pointer to string representation of the errno, that is invalidated
+ * upon the next call.
+ */
+const char *errstr(int err);
 #endif /* __LIBBPF_STR_ERROR_H */