Fix -Af F bug when F is not a regular file

Problem reported by Boris Gjenero in:
https://lists.gnu.org/r/bug-tar/2022-11/msg00001.html
* src/update.c (append_file): Don’t assume that FILE_NAME is a
regular file whose size can be determined before reading.
Instead, simply read from the file until its end is reached.

diff --git a/src/update.c b/src/update.c
index 5424e2cee484597201ce857a66013860840cf8be..44ab229d63aed5068be824c8422b929aebe16e08 100644 (file)
--- a/src/update.c
+++ b/src/update.c
@@ -50,7 +50,6 @@ static void
 append_file (char *file_name)
 {
   int handle = openat (chdir_fd, file_name, O_RDONLY | O_BINARY);
-  struct stat stat_data;
 
   if (handle < 0)
     {
@@ -58,43 +57,19 @@ append_file (char *file_name)
       return;
     }
 
-  if (fstat (handle, &stat_data) != 0)
-    stat_error (file_name);
-  else
+  while (true)
     {
-      off_t bytes_left = stat_data.st_size;
-
-      while (bytes_left > 0)
-       {
-         union block *start = find_next_block ();
-         size_t buffer_size = available_space_after (start);
-         size_t status;
-         char buf[UINTMAX_STRSIZE_BOUND];
-
-         if (bytes_left < buffer_size)
-           {
-             buffer_size = bytes_left;
-             status = buffer_size % BLOCKSIZE;
-             if (status)
-               memset (start->buffer + bytes_left, 0, BLOCKSIZE - status);
-           }
-
-         status = safe_read (handle, start->buffer, buffer_size);
-         if (status == SAFE_READ_ERROR)
-           read_fatal_details (file_name, stat_data.st_size - bytes_left,
-                               buffer_size);
-         if (status == 0)
-           FATAL_ERROR ((0, 0,
-                         ngettext ("%s: File shrank by %s byte",
-                                   "%s: File shrank by %s bytes",
-                                   bytes_left),
-                         quotearg_colon (file_name),
-                         STRINGIFY_BIGINT (bytes_left, buf)));
-
-         bytes_left -= status;
-
-         set_next_block_after (start + (status - 1) / BLOCKSIZE);
-       }
+      union block *start = find_next_block ();
+      size_t status = safe_read (handle, start->buffer,
+                                available_space_after (start));
+      if (status == 0)
+       break;
+      if (status == SAFE_READ_ERROR)
+       read_fatal (file_name);
+      if (status % BLOCKSIZE)
+       memset (start->buffer + status - status % BLOCKSIZE, 0,
+               BLOCKSIZE - status % BLOCKSIZE);
+      set_next_block_after (start + (status - 1) / BLOCKSIZE);
     }
 
   if (close (handle) != 0)