From 957903785aff716990a61c16b6531334c7019e97 Mon Sep 17 00:00:00 2001
From: Elliott Hughes <enh@google.com>
Date: Wed, 4 Jun 2025 14:08:22 +0000
Subject: [PATCH] dd: implement oflag=append and oflag=direct.

---
 lib/portability.h     |  7 ++++++-
 tests/dd.test         |  3 +++
 toys/pending/strace.c |  2 +-
 toys/posix/dd.c       | 16 +++++++++++-----
 4 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/lib/portability.h b/lib/portability.h
index 29d5469f..e87b919f 100644
--- a/lib/portability.h
+++ b/lib/portability.h
@@ -54,7 +54,8 @@
 // will transitively include it, and ones that don't (macOS) won't break.
 #include <sys/types.h>
 
-// Various constants old build environments might not have even if kernel does
+// Various constants old build environments (or glibc, hiding behind
+// _GNU_SOURCE) might not have even if kernel does.
 
 #ifndef AT_FDCWD             // Kernel commit 5590ff0d5528 2006
 #define AT_FDCWD -100
@@ -68,6 +69,10 @@
 #define AT_REMOVEDIR 0x200
 #endif
 
+#ifndef O_DIRECT
+#define O_DIRECT 0x4000
+#endif
+
 #ifndef RLIMIT_RTTIME // Commit 78f2c7db6068f 2008
 #define RLIMIT_RTTIME 15
 #endif
diff --git a/tests/dd.test b/tests/dd.test
index 11e869c9..b7bf5d4a 100644
--- a/tests/dd.test
+++ b/tests/dd.test
@@ -131,3 +131,6 @@ testing 'sync padding ticks down count' \
   'for i in one two three four five "$(seq 1 100)"
    do echo "$i"; sleep .1; done | dd bs=1024 count=5 conv=sync | sha1sum' \
   '02dcf1f497ccbe940f57818dfc34f2d0def8b3f9  -\n' '' ''
+
+echo -n "hello " > file
+testcmd "oflag=append" "of=file oflag=append conv=notrunc && cat file" "hello world\n" "" "world\n"
diff --git a/toys/pending/strace.c b/toys/pending/strace.c
index b5047851..f612f07c 100644
--- a/toys/pending/strace.c
+++ b/toys/pending/strace.c
@@ -374,7 +374,7 @@ static void print_flags(long v)
         C(O_CREAT), C(O_DIRECTORY), C(O_EXCL), C(O_NOCTTY), C(O_NOFOLLOW),
         C(O_TRUNC), C(O_ASYNC), C(O_APPEND), C(O_DSYNC), C(O_EXCL),
         C(O_NOATIME), C(O_NONBLOCK), C(O_PATH), C(O_SYNC),
-        0x4000, "O_DIRECT", 0x8000, "O_LARGEFILE", 0x410000, "O_TMPFILE", 0);
+        C(O_DIRECT), 0x8000, "O_LARGEFILE", 0x410000, "O_TMPFILE", 0);
   } else if (strstart(&TT.fmt, "prot|")) {
     print_bits(1,v,"PROT_NONE",C(PROT_READ),C(PROT_WRITE),C(PROT_EXEC),
 #if defined(PROT_BTI)
diff --git a/toys/posix/dd.c b/toys/posix/dd.c
index ebd55f10..7f392965 100644
--- a/toys/posix/dd.c
+++ b/toys/posix/dd.c
@@ -29,7 +29,9 @@ config DD
     These modifiers take a comma separated list of potential options:
 
     iflag=count_bytes,skip_bytes   count=N or skip=N is in bytes not blocks
-    oflag=seek_bytes,append        seek=N is in bytes, append output to file
+    oflag=
+      append      Append to file        direct   Skip caches
+      seek_bytes  seek=N is in bytes
     status=noxfer,none             don't show transfer rate, no summary info
     conv=
       notrunc  Don't truncate output    noerror  Continue after read errors
@@ -60,7 +62,7 @@ static const struct dd_flag dd_iflag[] = TAGGED_ARRAY(DD_iflag,
 );
 
 static const struct dd_flag dd_oflag[] = TAGGED_ARRAY(DD_oflag,
-  {"seek_bytes"},
+  {"append"}, {"direct"}, {"seek_bytes"},
 );
 
 static void status()
@@ -149,7 +151,7 @@ void dd_main()
     count = ULLONG_MAX, buflen;
   long long len;
   struct iovec iov[2];
-  int opos, olen, ifd = 0, ofd = 1, trunc = O_TRUNC, creat = O_CREAT, ii;
+  int opos, olen, ifd = 0, ofd = 1, trunc = O_TRUNC, oflags, ii;
   unsigned conv = 0, iflag = 0, oflag = 0;
 
   TT.show_xfer = TT.show_records = 1;
@@ -186,11 +188,15 @@ void dd_main()
   buf = xmalloc(buflen = ibs+obs*!bs);
   if (buflen<ibs || buflen<obs) error_exit("tilt");
 
-  if (conv & _DD_conv_nocreat) creat = 0;
+  oflags = O_CREAT|O_WRONLY;
+  if (conv & _DD_conv_nocreat) oflags &= ~O_CREAT;
   if (conv & _DD_conv_notrunc) trunc = 0;
+  if (oflag & _DD_oflag_append) oflags |= O_APPEND;
+  if (oflag & _DD_oflag_direct) oflags |= O_DIRECT;
+
   if (iname) ifd = xopenro(iname);
   else iname = "stdin";
-  if (oname) ofd = xcreate(oname, O_WRONLY|creat|(trunc*!seek),0666);
+  if (oname) ofd = xcreate(oname, oflags|(trunc*!seek), 0666);
   else oname = "stdout";
 
   // Implement skip=
-- 
2.39.5