Change the handling of circular buffers to not waste 4 bytes

all the time (we only waste from 1-3 bytes some of the time).

io.c

@@ -115,6 +115,17 @@ static char int_byte_extra[64] = {
 	2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 5, 6, /* (C0 - FF)/4 */
 };
 
+/* Our I/O buffers are sized with no bits on in the lowest byte of the "size"
+ * (indeed, our rounding of sizes in 1024-byte units assures more than this).
+ * This allows the code that is storing bytes near the physical end of a
+ * circular buffer to temporarily reduce the buffer's size (in order to make
+ * some storing idioms easier), while also making it simple to restore the
+ * buffer's actual size when the buffer's "pos" wraps around to the start (we
+ * just round the buffer's size up again). */
+
+#define IOBUF_WAS_REDUCED(siz) ((siz) & 0xFF)
+#define IOBUF_RESTORE_SIZE(siz) (((siz) | 0xFF) + 1)
+
 #define IN_MULTIPLEXED (iobuf.in_multiplexed)
 #define OUT_MULTIPLEXED (iobuf.out_empty_len != 0)
 
@@ -443,6 +454,39 @@ static void forward_filesfrom_data(void)
 	}
 }
 
+void reduce_iobuf_size(xbuf *out, size_t new_size)
+{
+	if (new_size < out->size) {
+		if (DEBUG_GTE(IO, 4)) {
+			const char *name = out == &iobuf.out ? "iobuf.out"
+					 : out == &iobuf.msg ? "iobuf.msg"
+					 : NULL;
+			if (name) {
+				rprintf(FINFO, "[%s] reduced size of %s (-%d)\n",
+					who_am_i(), name, (int)(out->size - new_size));
+			}
+		}
+		out->size = new_size;
+	}
+}
+
+void restore_iobuf_size(xbuf *out)
+{
+	if (IOBUF_WAS_REDUCED(out->size)) {
+		size_t new_size = IOBUF_RESTORE_SIZE(out->size);
+		if (DEBUG_GTE(IO, 4)) {
+			const char *name = out == &iobuf.out ? "iobuf.out"
+					 : out == &iobuf.msg ? "iobuf.msg"
+					 : NULL;
+			if (name) {
+				rprintf(FINFO, "[%s] restored size of %s (+%d)\n",
+					who_am_i(), name, (int)(new_size - out->size));
+			}
+		}
+		out->size = new_size;
+	}
+}
+
 /* Perform buffered input and output until specified conditions are met.  When
  * given a "needed" read requirement, we'll return without doing any I/O if the
  * iobuf.in bytes are already available.  When reading, we'll read as many
@@ -508,13 +552,12 @@ static char *perform_io(size_t needed, int flags)
 		 * Also make sure it will fit in the free space at the end, or
 		 * else we need to shift some bytes. */
 		if (needed && iobuf.in.size < needed) {
-			if (!(iobuf.in.buf = realloc_array(iobuf.in.buf, char, needed)))
-				out_of_memory("perform_io");
+			size_t new_size = ROUND_UP_1024(needed);
 			if (DEBUG_GTE(IO, 4)) {
-				rprintf(FINFO, "[%s] resized input buffer from %ld to %ld bytes.\n",
-					who_am_i(), (long)iobuf.in.size, (long)needed);
+				rprintf(FINFO, "[%s] resizing input buffer from %ld to %ld bytes.\n",
+					who_am_i(), (long)iobuf.in.size, (long)new_size);
 			}
-			iobuf.in.size = needed;
+			realloc_xbuf(&iobuf.in, new_size);
 		}
 		if (iobuf.in.size - iobuf.in.pos < needed
 		 || (iobuf.in.len < needed && iobuf.in.len < 1024
@@ -621,15 +664,6 @@ static char *perform_io(size_t needed, int flags)
 
 					SIVAL(iobuf.out.buf + iobuf.raw_data_header_pos, 0,
 					      ((MPLEX_BASE + (int)MSG_DATA)<<24) + iobuf.out.len - 4);
-					if (iobuf.raw_data_header_pos + 4 > iobuf.out.size) {
-						int siz = (int)(iobuf.raw_data_header_pos + 4 - iobuf.out.size);
-						/* We used some of the overflow bytes, so move them. */
-						if (DEBUG_GTE(IO, 4)) {
-							rprintf(FINFO, "[%s] wrap-bytes moved: %d (perform_io)\n",
-								who_am_i(), siz);
-						}
-						memcpy(iobuf.out.buf, iobuf.out.buf + iobuf.out.size, siz);
-					}
 
 					if (DEBUG_GTE(IO, 1)) {
 						rprintf(FINFO, "[%s] send_msg(%d, %ld)\n",
@@ -640,6 +674,13 @@ static char *perform_io(size_t needed, int flags)
 					iobuf.raw_data_header_pos = iobuf.raw_flushing_ends_before;
 					if (iobuf.raw_data_header_pos >= iobuf.out.size)
 						iobuf.raw_data_header_pos -= iobuf.out.size;
+					else if (iobuf.raw_data_header_pos + 4 > iobuf.out.size) {
+						/* The 4-byte header won't fit at the end of the buffer,
+						 * so we'll temporarily reduce the output buffer's size
+						 * and put the header at the start of the buffer. */
+						reduce_iobuf_size(&iobuf.out, iobuf.raw_data_header_pos);
+						iobuf.raw_data_header_pos = 0;
+					}
 					/* Yes, it is possible for this to make len > size for a while. */
 					iobuf.out.len += 4;
 				}
@@ -785,10 +826,12 @@ static char *perform_io(size_t needed, int flags)
 				if (iobuf.raw_flushing_ends_before)
 					iobuf.raw_flushing_ends_before -= out->size;
 				out->pos = 0;
+				restore_iobuf_size(out);
 			} else if (out->pos == iobuf.raw_flushing_ends_before)
 				iobuf.raw_flushing_ends_before = 0;
 			if ((out->len -= n) == empty_buf_len) {
 				out->pos = 0;
+				restore_iobuf_size(out);
 				if (empty_buf_len)
 					iobuf.raw_data_header_pos = 0;
 			}
@@ -832,7 +875,7 @@ void noop_io_until_death(void)
 int send_msg(enum msgcode code, const char *buf, size_t len, int convert)
 {
 	char *hdr;
-	size_t pos;
+	size_t needed, pos;
 	BOOL want_debug = DEBUG_GTE(IO, 1) && convert >= 0 && (msgs2stderr || code != MSG_INFO);
 
 	if (!OUT_MULTIPLEXED)
@@ -841,21 +884,32 @@ int send_msg(enum msgcode code, const char *buf, size_t len, int convert)
 	if (want_debug)
 		rprintf(FINFO, "[%s] send_msg(%d, %ld)\n", who_am_i(), (int)code, (long)len);
 
+	/* When checking for enough free space for this message, we need to
+	 * make sure that there is space for the 4-byte header, plus we'll
+	 * assume that we may waste up to 3 bytes (if the header doesn't fit
+	 * at the physical end of the buffer). */
 #ifdef ICONV_OPTION
 	if (convert > 0 && ic_send == (iconv_t)-1)
 		convert = 0;
 	if (convert > 0) {
 		/* Ensuring double-size room leaves space for maximal conversion expansion. */
-		if (iobuf.msg.len + len*2 + 4 > iobuf.msg.size)
-			perform_io(len*2 + 4, PIO_NEED_MSGROOM);
+		needed = len*2 + 4 + 3;
 	} else
 #endif
-	if (iobuf.msg.len + len + 4 > iobuf.msg.size)
-		perform_io(len + 4, PIO_NEED_MSGROOM);
+		needed = len + 4 + 3;
+	if (iobuf.msg.len + needed > iobuf.msg.size)
+		perform_io(needed, PIO_NEED_MSGROOM);
 
 	pos = iobuf.msg.pos + iobuf.msg.len; /* Must be set after any flushing. */
 	if (pos >= iobuf.msg.size)
 		pos -= iobuf.msg.size;
+	else if (pos + 4 > iobuf.msg.size) {
+		/* The 4-byte header won't fit at the end of the buffer,
+		 * so we'll temporarily reduce the message buffer's size
+		 * and put the header at the start of the buffer. */
+		reduce_iobuf_size(&iobuf.msg, pos);
+		pos = 0;
+	}
 	hdr = iobuf.msg.buf + pos;
 
 	iobuf.msg.len += 4; /* Allocate room for the coming header bytes. */
@@ -893,13 +947,6 @@ int send_msg(enum msgcode code, const char *buf, size_t len, int convert)
 	}
 
 	SIVAL(hdr, 0, ((MPLEX_BASE + (int)code)<<24) + len);
-	/* If the header used any overflow bytes, move them to the start. */
-	if ((pos = hdr+4 - iobuf.msg.buf) > iobuf.msg.size) {
-		int siz = (int)(pos - iobuf.msg.size);
-		if (DEBUG_GTE(IO, 4))
-			rprintf(FINFO, "[%s] wrap-bytes moved: %d (send_msg)\n", who_am_i(), siz);
-		memcpy(iobuf.msg.buf, iobuf.msg.buf + iobuf.msg.size, siz);
-	}
 
 	if (want_debug && convert > 0)
 		rprintf(FINFO, "[%s] converted msg len=%ld\n", who_am_i(), (long)len);
@@ -1169,13 +1216,6 @@ BOOL io_start_buffering_out(int f_out)
 	if (msgs2stderr && DEBUG_GTE(IO, 2))
 		rprintf(FINFO, "[%s] io_start_buffering_out(%d)\n", who_am_i(), f_out);
 
-	if (OUT_MULTIPLEXED && !iobuf.msg.buf) {
-		iobuf.msg.size = IO_BUFFER_SIZE - 4;
-		if (!(iobuf.msg.buf = new_array(char, iobuf.msg.size + 4)))
-			out_of_memory("io_start_buffering_out");
-		iobuf.msg.pos = iobuf.msg.len = 0;
-	}
-
 	if (iobuf.out.buf) {
 		if (iobuf.out_fd == -1)
 			iobuf.out_fd = f_out;
@@ -1184,11 +1224,7 @@ BOOL io_start_buffering_out(int f_out)
 		return False;
 	}
 
-	iobuf.out.size = IO_BUFFER_SIZE * 2 - 4;
-	/* The 4 overflow bytes makes some circular-buffer wrapping operations easier. */
-	if (!(iobuf.out.buf = new_array(char, iobuf.out.size + 4)))
-		out_of_memory("io_start_buffering_out");
-	iobuf.out.pos = iobuf.out.len = 0;
+	alloc_xbuf(&iobuf.out, ROUND_UP_1024(IO_BUFFER_SIZE * 2));
 	iobuf.out_fd = f_out;
 
 	return True;
@@ -1207,12 +1243,7 @@ BOOL io_start_buffering_in(int f_in)
 		return False;
 	}
 
-	iobuf.in.size = IO_BUFFER_SIZE;
-	if (!(iobuf.in.buf = new_array(char, iobuf.in.size)))
-		out_of_memory("io_start_buffering_in");
-
-	iobuf.in.pos = iobuf.in.len = 0;
-
+	alloc_xbuf(&iobuf.in, ROUND_UP_1024(IO_BUFFER_SIZE));
 	iobuf.in_fd = f_in;
 
 	return True;
@@ -2130,6 +2161,9 @@ void io_start_multiplex_out(int fd)
 	if (msgs2stderr && DEBUG_GTE(IO, 2))
 		rprintf(FINFO, "[%s] io_start_multiplex_out(%d)\n", who_am_i(), fd);
 
+	if (!iobuf.msg.buf)
+		alloc_xbuf(&iobuf.msg, ROUND_UP_1024(IO_BUFFER_SIZE));
+
 	iobuf.out_empty_len = 4; /* See also OUT_MULTIPLEXED */
 	io_start_buffering_out(fd);
 

rsync.c

@@ -133,42 +133,53 @@ void setup_iconv(void)
 # endif
 }
 
-/* Move any bytes in the overflow space to the start.  This avoids any issue
- * with a multibyte sequence that needs to span the end of the buffer. */
-static void wrap_overflow(xbuf *out, int siz)
-{
-	if (DEBUG_GTE(IO, 4))
-		rprintf(FINFO, "[%s] wrap-bytes moved: %d (iconvbufs)\n", who_am_i(), siz);
-	memcpy(out->buf, out->buf + out->size, siz);
-}
-
-/* This function converts the characters in the "in" xbuf into characters
- * in the "out" xbuf.  The "len" of the "in" xbuf is used starting from its
- * "pos".  The "size" of the "out" xbuf restricts how many characters can be
- * stored, starting at its "pos+len" position.  Note that the last byte of
- * the buffer is never used, which reserves space for a terminating '\0'.
- * If ICB_CIRCULAR_OUT is set, the output data can wrap around to the start,
- * and the buf IS ASSUMED TO HAVE AN EXTRA 4 BYTES OF OVERFLOW SPACE at the
- * end (the buffer will also not be expanded if it is already allocated).
+/* This function converts the chars in the "in" xbuf into characters in the
+ * "out" xbuf.  The ".len" chars of the "in" xbuf is used starting from its
+ * ".pos".  The ".size" of the "out" xbuf restricts how many characters can
+ * be stored, starting at its ".pos+.len" position.  Note that the last byte
+ * of the "out" xbuf is not used, which reserves space for a trailing '\0'
+ * (though it is up to the caller to store a trailing '\0', as needed).
+ *
  * We return a 0 on success or a -1 on error.  An error also sets errno to
  * E2BIG, EILSEQ, or EINVAL (see below); otherwise errno will be set to 0.
- * The "in" xbuf is altered to update "pos" and "len".  The "out" xbuf has
- * data appended, and its "len" incremented.   If ICB_EXPAND_OUT is set in
- * "flags", the "out" xbuf will also be allocated if empty, and expanded if
- * too small (so E2BIG will not be returned).  If ICB_INCLUDE_BAD is set in
- * "flags", any badly-encoded chars are included verbatim in the "out" xbuf,
- * so EILSEQ will not be returned.  Likewise for ICB_INCLUDE_INCOMPLETE with
- * respect to an incomplete multi-byte char at the end, which ensures that
- * EINVAL is not returned.  If ICB_INIT is set, the iconv() conversion state
- * is initialized prior to processing the characters. */
+ * The "in" xbuf is altered to update ".pos" and ".len".  The "out" xbuf has
+ * data appended, and its ".len" incremented (see below for a ".size" note).
+ *
+ * If ICB_CIRCULAR_OUT is set in "flags", the chars going into the "out" xbuf
+ * can wrap around to the start, and the xbuf may have its ".size" reduced
+ * (presumably by 1 byte) if the iconv code doesn't have space to store a
+ * multi-byte character at the physical end of the ".buf" (though no reducing
+ * happens if ".pos" is < 1, since there is no room to wrap around).
+ *
+ * If ICB_EXPAND_OUT is set in "flags", the "out" xbuf will be allocated if
+ * empty, and (as long as ICB_CIRCULAR_OUT is not set) expanded if too small.
+ * This prevents the return of E2BIG (except for a circular xbuf).
+ *
+ * If ICB_INCLUDE_BAD is set in "flags", any badly-encoded chars are included
+ * verbatim in the "out" xbuf, so EILSEQ will not be returned.
+ *
+ * If ICB_INCLUDE_INCOMPLETE is set in "flags", any incomplete multi-byte
+ * chars are included, which ensures that EINVAL is not returned.
+ *
+ * If ICB_INIT is set, the iconv() conversion state is initialized prior to
+ * processing the characters. */
 int iconvbufs(iconv_t ic, xbuf *in, xbuf *out, int flags)
 {
 	ICONV_CONST char *ibuf;
 	size_t icnt, ocnt, opos;
 	char *obuf;
 
-	if (!out->size && flags & ICB_EXPAND_OUT)
-		alloc_xbuf(out, 1024);
+	if (!out->size && flags & ICB_EXPAND_OUT) {
+		size_t siz = ROUND_UP_1024(in->len * 2);
+		alloc_xbuf(out, siz);
+	} else if (out->len+1 >= out->size) {
+		/* There is no room to even start storing data. */
+		if (!(flags & ICB_EXPAND_OUT) || flags & ICB_CIRCULAR_OUT) {
+			errno = E2BIG;
+			return -1;
+		}
+		realloc_xbuf(out, out->size + ROUND_UP_1024(in->len * 2));
+	}
 
 	if (flags & ICB_INIT)
 		iconv(ic, NULL, 0, NULL, 0);
@@ -180,12 +191,13 @@ int iconvbufs(iconv_t ic, xbuf *in, xbuf *out, int flags)
 	if (flags & ICB_CIRCULAR_OUT) {
 		if (opos >= out->size) {
 			opos -= out->size;
+			/* We know that out->pos is not 0 due to the "no room" check
+			 * above, so this can't go "negative". */
 			ocnt = out->pos - opos - 1;
 		} else {
-			/* We only make use of the 4 bytes of overflow buffer
-			 * if there is room to move the bytes to the start of
-			 * the circular buffer. */
-			ocnt = out->size - opos + MIN((ssize_t)out->pos - 1, 4);
+			/* Allow the use of all bytes to the physical end of the buffer
+			 * unless pos is 0, in which case we reserve our trailing '\0'. */
+			ocnt = out->size - opos - (out->pos ? 0 : 1);
 		}
 	} else
 		ocnt = out->size - opos - 1;
@@ -201,22 +213,32 @@ int iconvbufs(iconv_t ic, xbuf *in, xbuf *out, int flags)
 			} else if (errno == EILSEQ) {
 				if (!(flags & ICB_INCLUDE_BAD))
 					goto finish;
-			} else {
+			} else if (errno == E2BIG) {
+				size_t siz;
 				opos = obuf - out->buf;
-				if (flags & ICB_CIRCULAR_OUT && opos > out->size) {
-					wrap_overflow(out, opos -= out->size);
-					obuf = out->buf + opos;
-					if ((ocnt = out->pos - opos - 1) > 0)
-						continue;
+				if (flags & ICB_CIRCULAR_OUT && out->pos > 1 && opos > out->pos) {
+					/* We are in a divided circular buffer at the physical
+					 * end with room to wrap to the start.  If iconv() refused
+					 * to use one or more trailing bytes in the buffer, we
+					 * set the size to ignore the unused bytes. */
+					if (opos < out->size)
+						reduce_iobuf_size(out, opos);
+					obuf = out->buf;
+					ocnt = out->pos - 1;
+					continue;
 				}
 				if (!(flags & ICB_EXPAND_OUT) || flags & ICB_CIRCULAR_OUT) {
 					errno = E2BIG;
 					goto finish;
 				}
-				realloc_xbuf(out, out->size + 1024);
+				siz = ROUND_UP_1024(in->len * 2);
+				realloc_xbuf(out, out->size + siz);
 				obuf = out->buf + opos;
-				ocnt += 1024;
+				ocnt += siz;
 				continue;
+			} else {
+				rsyserr(FERROR, errno, "unexpected error from iconv()");
+				exit_cleanup(RERR_UNSUPPORTED);
 			}
 			*obuf++ = *ibuf++;
 			ocnt--, icnt--;
@@ -227,12 +249,8 @@ int iconvbufs(iconv_t ic, xbuf *in, xbuf *out, int flags)
 
   finish:
 	opos = obuf - out->buf;
-	if (flags & ICB_CIRCULAR_OUT) {
-		if (opos > out->size)
-			wrap_overflow(out, opos - out->size);
-		else if (opos < out->pos)
-			opos += out->size;
-	}
+	if (flags & ICB_CIRCULAR_OUT && opos < out->pos)
+		opos += out->size;
 	out->len = opos - out->pos;
 
 	in->len = icnt;

rsync.h

@@ -136,6 +136,8 @@
 /* For compatibility with older rsyncs */
 #define OLD_MAX_BLOCK_SIZE ((int32)1 << 29)
 
+#define ROUND_UP_1024(siz) ((siz) & (1024-1) ? ((siz) | (1024-1)) + 1 : (siz))
+
 #define IOERR_GENERAL	(1<<0) /* For backward compatibility, this must == 1 */
 #define IOERR_VANISHED	(1<<1)
 #define IOERR_DEL_LIMIT (1<<2)