mention failed operation in per-file warnings

on the one hand one can say it's ugly global state, on the other it's
totally handy!

just have to keep that in mind for MT, but it's rather obvious.

src/borg/archive.py

@@ -114,29 +114,40 @@ class BackupOSError(Exception):
 
     Any unwrapped IO error is critical and aborts execution (for example repository IO failure).
     """
-    def __init__(self, os_error):
+    def __init__(self, op, os_error):
+        self.op = op
         self.os_error = os_error
         self.errno = os_error.errno
         self.strerror = os_error.strerror
         self.filename = os_error.filename
 
     def __str__(self):
-        return str(self.os_error)
+        if self.op:
+            return '%s: %s' % (self.op, self.os_error)
+        else:
+            return str(self.os_error)
 
 
 class BackupIO:
+    op = ''
+
+    def __call__(self, op=''):
+        self.op = op
+        return self
+
     def __enter__(self):
         pass
 
     def __exit__(self, exc_type, exc_val, exc_tb):
         if exc_type and issubclass(exc_type, OSError):
-            raise BackupOSError(exc_val) from exc_val
+            raise BackupOSError(self.op, exc_val) from exc_val
 
 
 backup_io = BackupIO()
 
 
 def backup_io_iter(iterator):
+    backup_io.op = 'read'
     while True:
         try:
             with backup_io:
@@ -477,13 +488,13 @@ Number of files: {0.stats.nfiles}'''.format(
             pass
         mode = item.mode
         if stat.S_ISREG(mode):
-            with backup_io:
+            with backup_io('makedirs'):
                 if not os.path.exists(os.path.dirname(path)):
                     os.makedirs(os.path.dirname(path))
             # Hard link?
             if 'source' in item:
                 source = os.path.join(dest, *item.source.split(os.sep)[stripped_components:])
-                with backup_io:
+                with backup_io('link'):
                     if os.path.exists(path):
                         os.unlink(path)
                     if item.source not in hardlink_masters:
@@ -496,20 +507,20 @@ Number of files: {0.stats.nfiles}'''.format(
                         os.link(link_target, path)
                     return
                 # Extract chunks, since the item which had the chunks was not extracted
-            with backup_io:
+            with backup_io('open'):
                 fd = open(path, 'wb')
             with fd:
                 ids = [c.id for c in item.chunks]
                 for _, data in self.pipeline.fetch_many(ids, is_preloaded=True):
                     if pi:
                         pi.show(increase=len(data), info=[remove_surrogates(item.path)])
-                    with backup_io:
+                    with backup_io('write'):
                         if sparse and self.zeros.startswith(data):
                             # all-zero chunk: create a hole in a sparse file
                             fd.seek(len(data), 1)
                         else:
                             fd.write(data)
-                with backup_io:
+                with backup_io('truncate'):
                     pos = fd.tell()
                     fd.truncate(pos)
                     fd.flush()
@@ -556,6 +567,7 @@ Number of files: {0.stats.nfiles}'''.format(
 
         Does not access the repository.
         """
+        backup_io.op = 'attrs'
         uid = gid = None
         if not self.numeric_owner:
             uid = user2uid(item.user)
@@ -707,7 +719,7 @@ Number of files: {0.stats.nfiles}'''.format(
 
     def stat_ext_attrs(self, st, path):
         attrs = {}
-        with backup_io:
+        with backup_io('extended stat'):
             xattrs = xattr.get_all(path, follow_symlinks=False)
             bsdflags = get_flags(path, st)
             acl_get(path, attrs, st, self.numeric_owner)
@@ -744,7 +756,7 @@ Number of files: {0.stats.nfiles}'''.format(
             return 'b'  # block device
 
     def process_symlink(self, path, st):
-        with backup_io:
+        with backup_io('readlink'):
             source = os.readlink(path)
         item = Item(path=make_path_safe(path), source=source)
         item.update(self.stat_attrs(st, path))
@@ -856,7 +868,7 @@ Number of files: {0.stats.nfiles}'''.format(
         else:
             compress = self.compression_decider1.decide(path)
             self.file_compression_logger.debug('%s -> compression %s', path, compress['name'])
-            with backup_io:
+            with backup_io('open'):
                 fh = Archive._open_rb(path)
             with os.fdopen(fh, 'rb') as fd:
                 self.chunk_file(item, cache, self.stats, backup_io_iter(self.chunker.chunkify(fd, fh)), compress=compress)

src/borg/archiver.py

@@ -365,7 +365,7 @@ class Archiver:
             try:
                 st = os.lstat(path)
             except OSError as e:
-                self.print_warning('%s: %s', path, e)
+                self.print_warning('%s: stat: %s', path, e)
                 return
         if (st.st_ino, st.st_dev) in skip_inodes:
             return
@@ -380,7 +380,7 @@ class Archiver:
                 self.print_file_status('x', path)
                 return
         except OSError as e:
-            self.print_warning('%s: %s', path, e)
+            self.print_warning('%s: flags: %s', path, e)
             return
         if stat.S_ISREG(st.st_mode):
             if not dry_run:
@@ -407,7 +407,7 @@ class Archiver:
                     entries = helpers.scandir_inorder(path)
                 except OSError as e:
                     status = 'E'
-                    self.print_warning('%s: %s', path, e)
+                    self.print_warning('%s: scandir: %s', path, e)
                 else:
                     for dirent in entries:
                         normpath = os.path.normpath(dirent.path)