py/stream: Remove mp_stream_errno and use system errno instead.

This change is made for two reasons:

1. A 3rd-party library (eg berkeley-db-1.xx, axtls) may use the system
   provided errno for certain errors, and yet MicroPython stream objects
   that it calls will be using the internal mp_stream_errno.  So if the
   library returns an error it is not known whether the corresponding errno
   code is stored in the system errno or mp_stream_errno.  Using the system
   errno in all cases (eg in the mp_stream_posix_XXX wrappers) fixes this
   ambiguity.

2. For systems that have threading the system-provided errno should always
   be used because the errno value is thread-local.

For systems that do not have an errno, the new lib/embed/__errno.c file is
provided.

1 files changed, 5 insertions, 7 deletions

diff --git a/py/stream.c b/py/stream.c
index e6ffd3e2b..dce64a44d 100644
--- a/py/stream.c
+++ b/py/stream.c
@@ -503,14 +503,12 @@ MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_stream_ioctl_obj, 2, 3, stream_ioctl);
  * POSIX-compatible software to work with MicroPython streams.
  */
 
-// errno-like variable. If any of the functions below returned with error
-// status, this variable will contain error no.
-int mp_stream_errno;
+#include <errno.h>
 
 ssize_t mp_stream_posix_write(void *stream, const void *buf, size_t len) {
     mp_obj_base_t *o = stream;
     const mp_stream_p_t *stream_p = o->type->protocol;
-    mp_uint_t out_sz = stream_p->write(MP_OBJ_FROM_PTR(stream), buf, len, &mp_stream_errno);
+    mp_uint_t out_sz = stream_p->write(MP_OBJ_FROM_PTR(stream), buf, len, &errno);
     if (out_sz == MP_STREAM_ERROR) {
         return -1;
     } else {
@@ -521,7 +519,7 @@ ssize_t mp_stream_posix_write(void *stream, const void *buf, size_t len) {
 ssize_t mp_stream_posix_read(void *stream, void *buf, size_t len) {
     mp_obj_base_t *o = stream;
     const mp_stream_p_t *stream_p = o->type->protocol;
-    mp_uint_t out_sz = stream_p->read(MP_OBJ_FROM_PTR(stream), buf, len, &mp_stream_errno);
+    mp_uint_t out_sz = stream_p->read(MP_OBJ_FROM_PTR(stream), buf, len, &errno);
     if (out_sz == MP_STREAM_ERROR) {
         return -1;
     } else {
@@ -535,7 +533,7 @@ off_t mp_stream_posix_lseek(void *stream, off_t offset, int whence) {
     struct mp_stream_seek_t seek_s;
     seek_s.offset = offset;
     seek_s.whence = whence;
-    mp_uint_t res = stream_p->ioctl(MP_OBJ_FROM_PTR(stream), MP_STREAM_SEEK, (mp_uint_t)(uintptr_t)&seek_s, &mp_stream_errno);
+    mp_uint_t res = stream_p->ioctl(MP_OBJ_FROM_PTR(stream), MP_STREAM_SEEK, (mp_uint_t)(uintptr_t)&seek_s, &errno);
     if (res == MP_STREAM_ERROR) {
         return -1;
     }
@@ -545,7 +543,7 @@ off_t mp_stream_posix_lseek(void *stream, off_t offset, int whence) {
 int mp_stream_posix_fsync(void *stream) {
     mp_obj_base_t *o = stream;
     const mp_stream_p_t *stream_p = o->type->protocol;
-    mp_uint_t res = stream_p->ioctl(MP_OBJ_FROM_PTR(stream), MP_STREAM_FLUSH, 0, &mp_stream_errno);
+    mp_uint_t res = stream_p->ioctl(MP_OBJ_FROM_PTR(stream), MP_STREAM_FLUSH, 0, &errno);
     if (res == MP_STREAM_ERROR) {
         return -1;
     }