1 files changed, 225 insertions, 0 deletions
diff --git a/src/dns_ring.c b/src/dns_ring.c
new file mode 100644
index 0000000..01ce593
--- /dev/null
+++ b/src/dns_ring.c
@@ -0,0 +1,225 @@
+/*
+ * Ring buffer management
+ * This is a fork of ring.c for DNS usage.
+ *
+ * Copyright (C) 2000-2019 Willy Tarreau - w@1wt.eu
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation, version 2.1
+ * exclusively.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
+#include <stdlib.h>
+#include <haproxy/api.h>
+#include <haproxy/applet.h>
+#include <haproxy/buf.h>
+#include <haproxy/cli.h>
+#include <haproxy/dns_ring.h>
+#include <haproxy/sc_strm.h>
+#include <haproxy/stconn.h>
+#include <haproxy/thread.h>
+
+/* Initialize a pre-allocated ring with the buffer area
+ * of size */
+void dns_ring_init(struct dns_ring *ring, void *area, size_t size)
+{
+	HA_RWLOCK_INIT(&ring->lock);
+	MT_LIST_INIT(&ring->waiters);
+	ring->readers_count = 0;
+	ring->buf = b_make(area, size, 0, 0);
+	/* write the initial RC byte */
+	b_putchr(&ring->buf, 0);
+}
+
+/* Creates and returns a ring buffer of size <size> bytes. Returns NULL on
+ * allocation failure.
+ */
+struct dns_ring *dns_ring_new(size_t size)
+{
+	struct dns_ring *ring = NULL;
+	void *area = NULL;
+
+	if (size < 2)
+		goto fail;
+
+	ring = malloc(sizeof(*ring));
+	if (!ring)
+		goto fail;
+
+	area = malloc(size);
+	if (!area)
+		goto fail;
+
+	dns_ring_init(ring, area, size);
+	return ring;
+ fail:
+	free(area);
+	free(ring);
+	return NULL;
+}
+
+/* destroys and frees ring <ring> */
+void dns_ring_free(struct dns_ring *ring)
+{
+	if (!ring)
+		return;
+
+	free(ring->buf.area);
+	free(ring);
+}
+
+/* Tries to send <npfx> parts from <prefix> followed by <nmsg> parts from <msg>
+ * to ring <ring>. The message is sent atomically. It may be truncated to
+ * <maxlen> bytes if <maxlen> is non-null. There is no distinction between the
+ * two lists, it's just a convenience to help the caller prepend some prefixes
+ * when necessary. It takes the ring's write lock to make sure no other thread
+ * will touch the buffer during the update. Returns the number of bytes sent,
+ * or <=0 on failure.
+ */
+ssize_t dns_ring_write(struct dns_ring *ring, size_t maxlen, const struct ist pfx[], size_t npfx, const struct ist msg[], size_t nmsg)
+{
+	struct buffer *buf = &ring->buf;
+	struct appctx *appctx;
+	size_t totlen = 0;
+	size_t lenlen;
+	uint64_t dellen;
+	int dellenlen;
+	struct mt_list *elt1, elt2;
+	ssize_t sent = 0;
+	int i;
+
+	/* we have to find some room to add our message (the buffer is
+	 * never empty and at least contains the previous counter) and
+	 * to update both the buffer contents and heads at the same
+	 * time (it's doable using atomic ops but not worth the
+	 * trouble, let's just lock). For this we first need to know
+	 * the total message's length. We cannot measure it while
+	 * copying due to the varint encoding of the length.
+	 */
+	for (i = 0; i < npfx; i++)
+		totlen += pfx[i].len;
+	for (i = 0; i < nmsg; i++)
+		totlen += msg[i].len;
+
+	if (totlen > maxlen)
+		totlen = maxlen;
+
+	lenlen = varint_bytes(totlen);
+
+	HA_RWLOCK_WRLOCK(RING_LOCK, &ring->lock);
+	if (lenlen + totlen + 1 + 1 > b_size(buf))
+		goto done_buf;
+
+	while (b_room(buf) < lenlen + totlen + 1) {
+		/* we need to delete the oldest message (from the end),
+		 * and we have to stop if there's a reader stuck there.
+		 * Unless there's corruption in the buffer it's guaranteed
+		 * that we have enough data to find 1 counter byte, a
+		 * varint-encoded length (1 byte min) and the message
+		 * payload (0 bytes min).
+		 */
+		if (*b_head(buf))
+			goto done_buf;
+		dellenlen = b_peek_varint(buf, 1, &dellen);
+		if (!dellenlen)
+			goto done_buf;
+		BUG_ON(b_data(buf) < 1 + dellenlen + dellen);
+
+		b_del(buf, 1 + dellenlen + dellen);
+	}
+
+	/* OK now we do have room */
+	__b_put_varint(buf, totlen);
+
+	totlen = 0;
+	for (i = 0; i < npfx; i++) {
+		size_t len = pfx[i].len;
+
+		if (len + totlen > maxlen)
+			len = maxlen - totlen;
+		if (len)
+			__b_putblk(buf, pfx[i].ptr, len);
+		totlen += len;
+	}
+
+	for (i = 0; i < nmsg; i++) {
+		size_t len = msg[i].len;
+
+		if (len + totlen > maxlen)
+			len = maxlen - totlen;
+		if (len)
+			__b_putblk(buf, msg[i].ptr, len);
+		totlen += len;
+	}
+
+	*b_tail(buf) = 0; buf->data++; // new read counter
+	sent = lenlen + totlen + 1;
+
+	/* notify potential readers */
+	mt_list_for_each_entry_safe(appctx, &ring->waiters, wait_entry, elt1, elt2)
+		appctx_wakeup(appctx);
+
+ done_buf:
+	HA_RWLOCK_WRUNLOCK(RING_LOCK, &ring->lock);
+	return sent;
+}
+
+/* Tries to attach appctx <appctx> as a new reader on ring <ring>. This is
+ * meant to be used by low level appctx code such as CLI or ring forwarding.
+ * For higher level functions, please see the relevant parts in appctx or CLI.
+ * It returns non-zero on success or zero on failure if too many users are
+ * already attached. On success, the caller MUST call dns_ring_detach_appctx()
+ * to detach itself, even if it was never woken up.
+ */
+int dns_ring_attach(struct dns_ring *ring)
+{
+	int users = ring->readers_count;
+
+	do {
+		if (users >= 255)
+			return 0;
+	} while (!_HA_ATOMIC_CAS(&ring->readers_count, &users, users + 1));
+	return 1;
+}
+
+/* detach an appctx from a ring. The appctx is expected to be waiting at offset
+ * <ofs> relative to the beginning of the storage, or ~0 if not waiting yet.
+ * Nothing is done if <ring> is NULL.
+ */
+void dns_ring_detach_appctx(struct dns_ring *ring, struct appctx *appctx, size_t ofs)
+{
+	if (!ring)
+		return;
+
+	HA_RWLOCK_WRLOCK(RING_LOCK, &ring->lock);
+	if (ofs != ~0) {
+		/* reader was still attached */
+		if (ofs < b_head_ofs(&ring->buf))
+			ofs += b_size(&ring->buf) - b_head_ofs(&ring->buf);
+		else
+			ofs -= b_head_ofs(&ring->buf);
+
+		BUG_ON(ofs >= b_size(&ring->buf));
+		MT_LIST_DELETE(&appctx->wait_entry);
+		HA_ATOMIC_DEC(b_peek(&ring->buf, ofs));
+	}
+	HA_ATOMIC_DEC(&ring->readers_count);
+	HA_RWLOCK_WRUNLOCK(RING_LOCK, &ring->lock);
+}
+
+/*
+ * Local variables:
+ *  c-indent-level: 8
+ *  c-basic-offset: 8
+ * End:
+ */