dd: fix conv=noerror w/o sync to not write out zeroed blocks

function                                             old     new   delta
dd_main                                             1480    1463     -17

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 6 insertions, 5 deletions

diff --git a/coreutils/dd.c b/coreutils/dd.c
index 3fdfc236a..627e7e7b5 100644
--- a/coreutils/dd.c
+++ b/coreutils/dd.c
@@ -286,25 +286,26 @@ int dd_main(int argc UNUSED_PARAM, char **argv)
         }
 
         while (!(flags & FLAG_COUNT) || (G.in_full + G.in_part != count)) {
-                if (flags & FLAG_NOERROR) /* Pre-zero the buffer if conv=noerror */
-                        memset(ibuf, 0, ibs);
                 n = safe_read(ifd, ibuf, ibs);
                 if (n == 0)
                         break;
                 if (n < 0) {
+                        /* "Bad block" */
                         if (!(flags & FLAG_NOERROR))
                                 goto die_infile;
-                        n = ibs;
                         bb_simple_perror_msg(infile);
-                        /* GNU dd with conv=noerror skips over "bad blocks" */
+                        /* GNU dd with conv=noerror skips over bad blocks */
                         xlseek(ifd, ibs, SEEK_CUR);
+                        /* conv=noerror,sync writes NULs,
+                         * conv=noerror just ignores input bad blocks */
+                        n = 0;
                 }
                 if ((size_t)n == ibs)
                         G.in_full++;
                 else {
                         G.in_part++;
                         if (flags & FLAG_SYNC) {
-                                memset(ibuf + n, '\0', ibs - n);
+                                memset(ibuf + n, 0, ibs - n);
                                 n = ibs;
                         }
                 }