(skip): New arg COUNT_BYTES. Read with BLOCKSIZE

bytes, but consider RECORDS to be a byte count if COUNT_BYTES
is nonzero.

diff --git a/src/dd.c b/src/dd.c
index c8f8499e1201087ca5cae2e656f912de5fe9e281..b6b3a5897f064b96765c1bc17964d9ac48f4ae4d 100644 (file)
--- a/src/dd.c
+++ b/src/dd.c
@@ -783,21 +783,25 @@ buggy_lseek_support (int fdesc)
    nonzero.  */
 
 static void
-skip (int fdesc, char *file, uintmax_t records, size_t blocksize,
-      unsigned char *buf)
+skip (int fdesc, char *file, int count_bytes, uintmax_t records,
+      size_t blocksize, unsigned char *buf)
 {
-  off_t o;
+  size_t seek_blocksize = count_bytes ? 1 : blocksize;
+  off_t offset = records * seek_blocksize;
 
   /* Try lseek and if an error indicates it was an inappropriate
      operation, fall back on using read.  Some broken versions of
      lseek may return zero, so count that as an error too as a valid
      zero return is not possible here.  */
-  o = records * blocksize;
-  if (o / blocksize != records
+
+  if (offset / seek_blocksize != records
       || buggy_lseek_support (fdesc)
-      || lseek (fdesc, o, SEEK_CUR) <= 0)
+      || lseek (fdesc, offset, SEEK_CUR) <= 0)
     {
-      while (records-- > 0)
+      if (count_bytes)
+       records = offset;
+
+      while (records)
        {
          int nread;
 
@@ -812,6 +816,15 @@ skip (int fdesc, char *file, uintmax_t records, size_t blocksize,
             FIXME: maybe give a warning.  */
          if (nread == 0)
            break;
+
+         if (count_bytes)
+           {
+             records -= nread;
+             if (records < blocksize)
+               blocksize = records;
+           }
+         else
+           records--;
        }
     }
 }
@@ -961,8 +974,8 @@ dd_copy (void)
     }
 
   if (skip_records != 0)
-    skip (STDIN_FILENO, input_file, skip_records,
-         skip_bytes ? 1 : input_blocksize, ibuf);
+    skip (STDIN_FILENO, input_file, skip_bytes, skip_records,
+         input_blocksize, ibuf);
 
   if (seek_records != 0)
     {
@@ -973,8 +986,8 @@ dd_copy (void)
         0+0 records out
         */
 
-      skip (STDOUT_FILENO, output_file, seek_records,
-           seek_bytes ? 1 : output_blocksize, obuf);
+      skip (STDOUT_FILENO, output_file, seek_bytes, seek_records,
+           output_blocksize, obuf);
     }
 
   if (max_records == 0)