src/ring.c - haproxy - Gitiles

 /*
  * Ring buffer management
  *
  * 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/conn_stream.h>
 #include <haproxy/cs_utils.h>
 #include <haproxy/ring.h>
 #include <haproxy/thread.h>

 /* Initialize a pre-allocated ring with the buffer area
  * of size */
 void ring_init(struct ring *ring, void *area, size_t size)
 {
 	HA_RWLOCK_INIT(&ring->lock);
 	LIST_INIT(&ring->waiters);
 	ring->readers_count = 0;
 	ring->ofs = 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 ring *ring_new(size_t size)
 {
 	struct 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;

 	ring_init(ring, area, size);
 	return ring;
  fail:
 	free(area);
 	free(ring);
 	return NULL;
 }

 /* Resizes existing ring <ring> to <size> which must be larger, without losing
  * its contents. The new size must be at least as large as the previous one or
  * no change will be performed. The pointer to the ring is returned on success,
  * or NULL on allocation failure. This will lock the ring for writes.
  */
 struct ring *ring_resize(struct ring *ring, size_t size)
 {
 	void *area;

 	if (b_size(&ring->buf) >= size)
 		return ring;

 	area = malloc(size);
 	if (!area)
 		return NULL;

 	HA_RWLOCK_WRLOCK(LOGSRV_LOCK, &ring->lock);

 	/* recheck the buffer's size, it may have changed during the malloc */
 	if (b_size(&ring->buf) < size) {
 		/* copy old contents */
 		b_getblk(&ring->buf, area, ring->buf.data, 0);
 		area = HA_ATOMIC_XCHG(&ring->buf.area, area);
 		ring->buf.size = size;
 		ring->buf.head = 0;
 	}

 	HA_RWLOCK_WRUNLOCK(LOGSRV_LOCK, &ring->lock);

 	free(area);
 	return ring;
 }

 /* destroys and frees ring <ring> */
 void ring_free(struct 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 ring_write(struct 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;
 	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(LOGSRV_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);
 		ring->ofs += 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 */
 	list_for_each_entry(appctx, &ring->waiters, wait_entry)
 		appctx_wakeup(appctx);

  done_buf:
 	HA_RWLOCK_WRUNLOCK(LOGSRV_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 ring_detach_appctx()
  * to detach itself, even if it was never woken up.
  */
 int ring_attach(struct 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>. Nothing is done if <ring> is NULL.
  */
 void ring_detach_appctx(struct ring *ring, struct appctx *appctx, size_t ofs)
 {
 	if (!ring)
 		return;

 	HA_RWLOCK_WRLOCK(LOGSRV_LOCK, &ring->lock);
 	if (ofs != ~0) {
 		/* reader was still attached */
 		ofs -= ring->ofs;
 		BUG_ON(ofs >= b_size(&ring->buf));
 		LIST_DEL_INIT(&appctx->wait_entry);
 		HA_ATOMIC_DEC(b_peek(&ring->buf, ofs));
 	}
 	HA_ATOMIC_DEC(&ring->readers_count);
 	HA_RWLOCK_WRUNLOCK(LOGSRV_LOCK, &ring->lock);
 }

 /* Tries to attach CLI handler <appctx> as a new reader on ring <ring>. This is
  * meant to be used when registering a CLI function to dump a buffer, so it
  * returns zero on success, or non-zero on failure with a message in the appctx
  * CLI context. It automatically sets the io_handler and io_release callbacks if
  * they were not set.
  */
 int ring_attach_cli(struct ring *ring, struct appctx *appctx)
 {
 	if (!ring_attach(ring))
 		return cli_err(appctx,
 		               "Sorry, too many watchers (255) on this ring buffer. "
 		               "What could it have so interesting to attract so many watchers ?");

 	if (!appctx->io_handler)
 		appctx->io_handler = cli_io_handler_show_ring;
 	if (!appctx->io_release)
                 appctx->io_release = cli_io_release_show_ring;
 	appctx->ctx.cli.p0 = ring;
 	appctx->ctx.cli.o0 = ~0; // start from the oldest event
 	return 0;
 }

 /* This function dumps all events from the ring whose pointer is in <p0> into
  * the appctx's output buffer, and takes from <o0> the seek offset into the
  * buffer's history (0 for oldest known event). It looks at <i0> for boolean
  * options: bit0 means it must wait for new data or any key to be pressed. Bit1
  * means it must seek directly to the end to wait for new contents. It returns
  * 0 if the output buffer or events are missing is full and it needs to be
  * called again, otherwise non-zero. It is meant to be used with
  * cli_release_show_ring() to clean up.
  */
 int cli_io_handler_show_ring(struct appctx *appctx)
 {
 	struct conn_stream *cs = appctx->owner;
 	struct ring *ring = appctx->ctx.cli.p0;
 	struct buffer *buf = &ring->buf;
 	size_t ofs = appctx->ctx.cli.o0;
 	uint64_t msg_len;
 	size_t len, cnt;
 	int ret;

 	if (unlikely(cs_ic(cs)->flags & (CF_WRITE_ERROR|CF_SHUTW)))
 		return 1;

 	HA_RWLOCK_WRLOCK(LOGSRV_LOCK, &ring->lock);
 	LIST_DEL_INIT(&appctx->wait_entry);
 	HA_RWLOCK_WRUNLOCK(LOGSRV_LOCK, &ring->lock);

 	HA_RWLOCK_RDLOCK(LOGSRV_LOCK, &ring->lock);

 	/* explanation for the initialization below: it would be better to do
 	 * this in the parsing function but this would occasionally result in
 	 * dropped events because we'd take a reference on the oldest message
 	 * and keep it while being scheduled. Thus instead let's take it the
 	 * first time we enter here so that we have a chance to pass many
 	 * existing messages before grabbing a reference to a location. This
 	 * value cannot be produced after initialization.
 	 */
 	if (unlikely(ofs == ~0)) {
 		ofs = 0;

 		/* going to the end means looking at tail-1 */
 		if (appctx->ctx.cli.i0 & 2)
 			ofs += b_data(buf) - 1;

 		HA_ATOMIC_INC(b_peek(buf, ofs));
 		ofs += ring->ofs;
 	}

 	/* we were already there, adjust the offset to be relative to
 	 * the buffer's head and remove us from the counter.
 	 */
 	ofs -= ring->ofs;
 	BUG_ON(ofs >= buf->size);
 	HA_ATOMIC_DEC(b_peek(buf, ofs));

 	/* in this loop, ofs always points to the counter byte that precedes
 	 * the message so that we can take our reference there if we have to
 	 * stop before the end (ret=0).
 	 */
 	ret = 1;
 	while (ofs + 1 < b_data(buf)) {
 		cnt = 1;
 		len = b_peek_varint(buf, ofs + cnt, &msg_len);
 		if (!len)
 			break;
 		cnt += len;
 		BUG_ON(msg_len + ofs + cnt + 1 > b_data(buf));

 		if (unlikely(msg_len + 1 > b_size(&trash))) {
 			/* too large a message to ever fit, let's skip it */
 			ofs += cnt + msg_len;
 			continue;
 		}

 		chunk_reset(&trash);
 		len = b_getblk(buf, trash.area, msg_len, ofs + cnt);
 		trash.data += len;
 		trash.area[trash.data++] = '\n';

 		if (ci_putchk(cs_ic(cs), &trash) == -1) {
 			cs_rx_room_blk(cs);
 			ret = 0;
 			break;
 		}
 		ofs += cnt + msg_len;
 	}

 	HA_ATOMIC_INC(b_peek(buf, ofs));
 	ofs += ring->ofs;
 	appctx->ctx.cli.o0 = ofs;
 	HA_RWLOCK_RDUNLOCK(LOGSRV_LOCK, &ring->lock);

 	if (ret && (appctx->ctx.cli.i0 & 1)) {
 		/* we've drained everything and are configured to wait for more
 		 * data or an event (keypress, close)
 		 */
 		if (!cs_oc(cs)->output && !(cs_oc(cs)->flags & CF_SHUTW)) {
 			/* let's be woken up once new data arrive */
 			HA_RWLOCK_WRLOCK(LOGSRV_LOCK, &ring->lock);
 			LIST_APPEND(&ring->waiters, &appctx->wait_entry);
 			HA_RWLOCK_WRUNLOCK(LOGSRV_LOCK, &ring->lock);
 			cs_rx_endp_done(cs);
 			ret = 0;
 		}
 		/* always drain all the request */
 		co_skip(cs_oc(cs), cs_oc(cs)->output);
 	}
 	return ret;
 }

 /* must be called after cli_io_handler_show_ring() above */
 void cli_io_release_show_ring(struct appctx *appctx)
 {
 	struct ring *ring = appctx->ctx.cli.p0;
 	size_t ofs = appctx->ctx.cli.o0;

 	ring_detach_appctx(ring, appctx, ofs);
 }


 /*
  * Local variables:
  *  c-indent-level: 8
  *  c-basic-offset: 8
  * End:
  */
	/*
	* Ring buffer management
	*
	* 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/conn_stream.h>
	#include <haproxy/cs_utils.h>
	#include <haproxy/ring.h>
	#include <haproxy/thread.h>

	/* Initialize a pre-allocated ring with the buffer area
	* of size */
	void ring_init(struct ring ring, void area, size_t size)
	{
	HA_RWLOCK_INIT(&ring->lock);
	LIST_INIT(&ring->waiters);
	ring->readers_count = 0;
	ring->ofs = 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 ring *ring_new(size_t size)
	{
	struct 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;

	ring_init(ring, area, size);
	return ring;
	fail:
	free(area);
	free(ring);
	return NULL;
	}

	/* Resizes existing ring <ring> to <size> which must be larger, without losing
	* its contents. The new size must be at least as large as the previous one or
	* no change will be performed. The pointer to the ring is returned on success,
	* or NULL on allocation failure. This will lock the ring for writes.
	*/
	struct ring ring_resize(struct ring ring, size_t size)
	{
	void *area;

	if (b_size(&ring->buf) >= size)
	return ring;

	area = malloc(size);
	if (!area)
	return NULL;

	HA_RWLOCK_WRLOCK(LOGSRV_LOCK, &ring->lock);

	/* recheck the buffer's size, it may have changed during the malloc */
	if (b_size(&ring->buf) < size) {
	/* copy old contents */
	b_getblk(&ring->buf, area, ring->buf.data, 0);
	area = HA_ATOMIC_XCHG(&ring->buf.area, area);
	ring->buf.size = size;
	ring->buf.head = 0;
	}

	HA_RWLOCK_WRUNLOCK(LOGSRV_LOCK, &ring->lock);

	free(area);
	return ring;
	}

	/* destroys and frees ring <ring> */
	void ring_free(struct 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 ring_write(struct 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;
	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(LOGSRV_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);
	ring->ofs += 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 */
	list_for_each_entry(appctx, &ring->waiters, wait_entry)
	appctx_wakeup(appctx);

	done_buf:
	HA_RWLOCK_WRUNLOCK(LOGSRV_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 ring_detach_appctx()
	* to detach itself, even if it was never woken up.
	*/
	int ring_attach(struct 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>. Nothing is done if <ring> is NULL.
	*/
	void ring_detach_appctx(struct ring ring, struct appctx appctx, size_t ofs)
	{
	if (!ring)
	return;

	HA_RWLOCK_WRLOCK(LOGSRV_LOCK, &ring->lock);
	if (ofs != ~0) {
	/* reader was still attached */
	ofs -= ring->ofs;
	BUG_ON(ofs >= b_size(&ring->buf));
	LIST_DEL_INIT(&appctx->wait_entry);
	HA_ATOMIC_DEC(b_peek(&ring->buf, ofs));
	}
	HA_ATOMIC_DEC(&ring->readers_count);
	HA_RWLOCK_WRUNLOCK(LOGSRV_LOCK, &ring->lock);
	}

	/* Tries to attach CLI handler <appctx> as a new reader on ring <ring>. This is
	* meant to be used when registering a CLI function to dump a buffer, so it
	* returns zero on success, or non-zero on failure with a message in the appctx
	* CLI context. It automatically sets the io_handler and io_release callbacks if
	* they were not set.
	*/
	int ring_attach_cli(struct ring ring, struct appctx appctx)
	{
	if (!ring_attach(ring))
	return cli_err(appctx,
	"Sorry, too many watchers (255) on this ring buffer. "
	"What could it have so interesting to attract so many watchers ?");

	if (!appctx->io_handler)
	appctx->io_handler = cli_io_handler_show_ring;
	if (!appctx->io_release)
	appctx->io_release = cli_io_release_show_ring;
	appctx->ctx.cli.p0 = ring;
	appctx->ctx.cli.o0 = ~0; // start from the oldest event
	return 0;
	}

	/* This function dumps all events from the ring whose pointer is in <p0> into
	* the appctx's output buffer, and takes from <o0> the seek offset into the
	* buffer's history (0 for oldest known event). It looks at <i0> for boolean
	* options: bit0 means it must wait for new data or any key to be pressed. Bit1
	* means it must seek directly to the end to wait for new contents. It returns
	* 0 if the output buffer or events are missing is full and it needs to be
	* called again, otherwise non-zero. It is meant to be used with
	* cli_release_show_ring() to clean up.
	*/
	int cli_io_handler_show_ring(struct appctx *appctx)
	{
	struct conn_stream *cs = appctx->owner;
	struct ring *ring = appctx->ctx.cli.p0;
	struct buffer *buf = &ring->buf;
	size_t ofs = appctx->ctx.cli.o0;
	uint64_t msg_len;
	size_t len, cnt;
	int ret;

	if (unlikely(cs_ic(cs)->flags & (CF_WRITE_ERROR\|CF_SHUTW)))
	return 1;

	HA_RWLOCK_WRLOCK(LOGSRV_LOCK, &ring->lock);
	LIST_DEL_INIT(&appctx->wait_entry);
	HA_RWLOCK_WRUNLOCK(LOGSRV_LOCK, &ring->lock);

	HA_RWLOCK_RDLOCK(LOGSRV_LOCK, &ring->lock);

	/* explanation for the initialization below: it would be better to do
	* this in the parsing function but this would occasionally result in
	* dropped events because we'd take a reference on the oldest message
	* and keep it while being scheduled. Thus instead let's take it the
	* first time we enter here so that we have a chance to pass many
	* existing messages before grabbing a reference to a location. This
	* value cannot be produced after initialization.
	*/
	if (unlikely(ofs == ~0)) {
	ofs = 0;

	/* going to the end means looking at tail-1 */
	if (appctx->ctx.cli.i0 & 2)
	ofs += b_data(buf) - 1;

	HA_ATOMIC_INC(b_peek(buf, ofs));
	ofs += ring->ofs;
	}

	/* we were already there, adjust the offset to be relative to
	* the buffer's head and remove us from the counter.
	*/
	ofs -= ring->ofs;
	BUG_ON(ofs >= buf->size);
	HA_ATOMIC_DEC(b_peek(buf, ofs));

	/* in this loop, ofs always points to the counter byte that precedes
	* the message so that we can take our reference there if we have to
	* stop before the end (ret=0).
	*/
	ret = 1;
	while (ofs + 1 < b_data(buf)) {
	cnt = 1;
	len = b_peek_varint(buf, ofs + cnt, &msg_len);
	if (!len)
	break;
	cnt += len;
	BUG_ON(msg_len + ofs + cnt + 1 > b_data(buf));

	if (unlikely(msg_len + 1 > b_size(&trash))) {
	/* too large a message to ever fit, let's skip it */
	ofs += cnt + msg_len;
	continue;
	}

	chunk_reset(&trash);
	len = b_getblk(buf, trash.area, msg_len, ofs + cnt);
	trash.data += len;
	trash.area[trash.data++] = '\n';

	if (ci_putchk(cs_ic(cs), &trash) == -1) {
	cs_rx_room_blk(cs);
	ret = 0;
	break;
	}
	ofs += cnt + msg_len;
	}

	HA_ATOMIC_INC(b_peek(buf, ofs));
	ofs += ring->ofs;
	appctx->ctx.cli.o0 = ofs;
	HA_RWLOCK_RDUNLOCK(LOGSRV_LOCK, &ring->lock);

	if (ret && (appctx->ctx.cli.i0 & 1)) {
	/* we've drained everything and are configured to wait for more
	* data or an event (keypress, close)
	*/
	if (!cs_oc(cs)->output && !(cs_oc(cs)->flags & CF_SHUTW)) {
	/* let's be woken up once new data arrive */
	HA_RWLOCK_WRLOCK(LOGSRV_LOCK, &ring->lock);
	LIST_APPEND(&ring->waiters, &appctx->wait_entry);
	HA_RWLOCK_WRUNLOCK(LOGSRV_LOCK, &ring->lock);
	cs_rx_endp_done(cs);
	ret = 0;
	}
	/* always drain all the request */
	co_skip(cs_oc(cs), cs_oc(cs)->output);
	}
	return ret;
	}

	/* must be called after cli_io_handler_show_ring() above */
	void cli_io_release_show_ring(struct appctx *appctx)
	{
	struct ring *ring = appctx->ctx.cli.p0;
	size_t ofs = appctx->ctx.cli.o0;

	ring_detach_appctx(ring, appctx, ofs);
	}


	/*
	* Local variables:
	* c-indent-level: 8
	* c-basic-offset: 8
	* End:
	*/