Count short read slop when seeking

* src/buffer.c (short_read_slop): New static var.
(get_archive_status): Treat anything other than fifos and sockets
as potentially seekable; they’ll tell us if they aren’t, whereas
fifos and sockets cannot be seekable.  Check named files for
initial offset too, to deal with names like /dev/stdin.
Do not worry about start_offset’s value if !seekable_archive,
as it won’t be used.  Use short_read_slop.
(short_read, try_new_volume, simple_flush_read, _gnu_flush_read):
Set short_read_slop.

diff --git a/src/buffer.c b/src/buffer.c
index 7b0064455384cb297e98672b29cb9c5a2f9c2366..6b55af26d9a415af310d7cced5949e6bff9c71eb 100644 (file)
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -47,6 +47,7 @@ static tarlong prev_written;    /* bytes written on previous volumes */
 static tarlong bytes_written;   /* bytes written on this volume */
 static void *record_buffer[2];  /* allocated memory */
 static bool record_index;
+static idx_t short_read_slop;  /* excess bytes at end of short read */
 
 /* FIXME: The following variables should ideally be static to this
    module.  However, this cannot be done yet.  The cleanup continues!  */
@@ -703,22 +704,20 @@ get_archive_status (enum access_mode wanted_access, bool backed_up_flag)
     = (! (multi_volume_option || use_compress_program_option)
        && (seek_option < 0
           ? (_isrmt (archive)
-             || S_ISREG (archive_stat.st_mode)
-             || S_ISBLK (archive_stat.st_mode))
-          : seek_option));
+             || ! (S_ISFIFO (archive_stat.st_mode)
+                   || S_ISSOCK (archive_stat.st_mode)))
+          : seek_option != 0));
 
   if (wanted_access == ACCESS_READ)
     {
-      if (archive == STDIN_FILENO && seekable_archive)
+      if (seekable_archive)
        {
-         start_offset = lseek (archive, 0, SEEK_CUR);
-         if (start_offset == -1)
+         start_offset = (lseek (archive, 0, SEEK_CUR)
+                         - (record_end - record_start) * BLOCKSIZE
+                         - short_read_slop);
+         if (start_offset < 0)
            seekable_archive = false;
-         else
-           start_offset -= (record_end - record_start) * BLOCKSIZE;
        }
-      else
-       start_offset = 0;
     }
   else
     sys_detect_dev_null_output ();
@@ -999,7 +998,7 @@ short_read (idx_t status)
 
          paxfatal (0, ngettext ("Unaligned block (%td byte) in archive",
                                 "Unaligned block (%td bytes) in archive",
-                                  rest),
+                                rest),
                    rest);
         }
 
@@ -1008,6 +1007,7 @@ short_read (idx_t status)
     }
 
   record_end = record_start + (record_size - left) / BLOCKSIZE;
+  short_read_slop = (record_size - left) % BLOCKSIZE;
   records_read++;
 }
 
@@ -1451,6 +1451,7 @@ try_new_volume (void)
          < 0)
     archive_read_error ();
 
+  short_read_slop = 0;
   if (status != record_size)
     short_read (status);
 
@@ -1813,6 +1814,7 @@ simple_flush_read (void)
   ptrdiff_t nread;
   while ((nread = rmtread (archive, record_start->buffer, record_size)) < 0)
     archive_read_error ();
+  short_read_slop = 0;
   if (nread == record_size)
     records_read++;
   else
@@ -1873,10 +1875,14 @@ _gnu_flush_read (void)
        /* Necessary for blocking_factor == 1 */
        flush_archive ();
     }
-  else if (nread == record_size)
-    records_read++;
   else
-    short_read (nread);
+    {
+      short_read_slop = 0;
+      if (nread == record_size)
+       records_read++;
+      else
+       short_read (nread);
+    }
 }
 
 static void