summaryrefslogtreecommitdiffstats
path: root/src/dns_ring.c
diff options
context:
space:
mode:
Diffstat (limited to '')
-rw-r--r--src/dns_ring.c225
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:
+ */