Added dbgerr.py for debugging littlefs's error codes

This is based on moreutils's errno program, but specialized for
littlefs's error codes. Everything is hardcoded in dbgerr.py, so this
should be portable to any OS really.

Hopefully this will be useful for debugging littlefs errors:

  $ ./scripts/dbgerr.py -84
  LFS_ERR_CORRUPT -84 Corrupted

scripts/dbgerr.py

@@ -0,0 +1,96 @@
+#!/usr/bin/env python3
+
+
+ERRS = [
+    ('OK',              0,      "No error"                          ),
+    ('UNKNOWN',         -1,     "Unknown error"                     ),
+    ('INVAL',           -22,    "Invalid parameter"                 ),
+    ('NOTSUP',          -95,    "Operation not supported"           ),
+    ('IO',              -5,     "Error during device operation"     ),
+    ('CORRUPT',         -84,    "Corrupted"                         ),
+    ('NOENT',           -2,     "No directory entry"                ),
+    ('EXIST',           -17,    "Entry already exists"              ),
+    ('NOTDIR',          -20,    "Entry is not a dir"                ),
+    ('ISDIR',           -21,    "Entry is a dir"                    ),
+    ('NOTEMPTY',        -39,    "Dir is not empty"                  ),
+    ('FBIG',            -27,    "File too large"                    ),
+    ('NOSPC',           -28,    "No space left on device"           ),
+    ('NOMEM',           -12,    "No more memory available"          ),
+    ('NOATTR',          -61,    "No data/attr available"            ),
+    ('NAMETOOLONG',     -36,    "File name too long"                ),
+    ('RANGE',           -34,    "Result out of range"               ),
+]
+
+
+def main(errs, *,
+        list=False):
+    list_, list = list, __builtins__.list
+
+    # list all known error codes
+    if list_:
+        # first find the widths
+        w = [0, 0]
+        for n, e, h in ERRS:
+            w[0] = max(w[0], len('LFS_ERR_')+len(n))
+            w[1] = max(w[1], len(str(e)))
+
+        # print
+        for n, e, h in ERRS:
+            print('%-*s %-*s %s' % (
+                w[0], 'LFS_ERR_'+n,
+                w[1], e,
+                h))
+
+    # find these errors
+    else:
+        def find_err(err):
+            # find by LFS_ERR_+name
+            for n, e, h in ERRS:
+                if 'LFS_ERR_'+n == err:
+                    return n, e, h
+            # find by name
+            for n, e, h in ERRS:
+                if n == err:
+                    return n, e, h
+            # find by E+name
+            for n, e, h in ERRS:
+                if 'E'+n == err:
+                    return n, e, h
+            try:
+                # find by err code
+                for n, e, h in ERRS:
+                    if e == int(err, 0):
+                        return n, e, h
+                # find by negated err code
+                for n, e, h in ERRS:
+                    if e == -int(err, 0):
+                        return n, e, h
+            except ValueError:
+                pass
+            # not found
+            raise KeyError(err)
+
+        for err in errs:
+            try:
+                n, e, h = find_err(err)
+                print('%s %s %s' % ('LFS_ERR_'+n, e, h))
+            except KeyError:
+                print('%s ?' % err)
+
+if __name__ == "__main__":
+    import argparse
+    import sys
+    parser = argparse.ArgumentParser(
+        description="Decode littlefs error codes.",
+        allow_abbrev=False)
+    parser.add_argument(
+        'errs',
+        nargs='*',
+        help="Error codes or error names to decode.")
+    parser.add_argument(
+        '-l', '--list',
+        action='store_true',
+        help="List all known error codes.")
+    sys.exit(main(**{k: v
+        for k, v in vars(parser.parse_intermixed_args()).items()
+        if v is not None}))