X-Git-Url: https://git.lttng.org/?p=lttng-tools.git;a=blobdiff_plain;f=src%2Fbin%2Flttng%2Fcommands%2Fenable_channels.cpp;fp=src%2Fbin%2Flttng%2Fcommands%2Fenable_channels.cpp;h=194ec541eae167077597997fce467e3f10c101bd;hp=0000000000000000000000000000000000000000;hb=48a4000561343808724f7cb5fa8c131877489ccd;hpb=81663f073dbfb4b61c06a0ceb8ca33c4fc41b1c5

diff --git a/src/bin/lttng/commands/enable_channels.cpp b/src/bin/lttng/commands/enable_channels.cpp
new file mode 100644
index 000000000..194ec541e
--- /dev/null
+++ b/src/bin/lttng/commands/enable_channels.cpp
@@ -0,0 +1,759 @@
+/*
+ * Copyright (C) 2011 David Goulet <david.goulet@polymtl.ca>
+ *
+ * SPDX-License-Identifier: GPL-2.0-only
+ *
+ */
+
+#define _LGPL_SOURCE
+#include <popt.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <inttypes.h>
+#include <ctype.h>
+
+#include <common/sessiond-comm/sessiond-comm.h>
+#include <common/utils.h>
+#include <common/mi-lttng.h>
+
+#include <lttng/domain-internal.h>
+
+#include "../command.h"
+#include "../utils.h"
+
+
+static struct lttng_channel chan_opts;
+static char *opt_channels;
+static int opt_kernel;
+static char *opt_session_name;
+static int opt_userspace;
+static char *opt_output;
+static int opt_buffer_uid;
+static int opt_buffer_pid;
+static int opt_buffer_global;
+static struct {
+	bool set;
+	uint64_t interval;
+} opt_monitor_timer;
+static struct {
+	bool set;
+	int64_t value;
+} opt_blocking_timeout;
+
+static struct mi_writer *writer;
+
+#ifdef LTTNG_EMBED_HELP
+static const char help_msg[] =
+#include <lttng-enable-channel.1.h>
+;
+#endif
+
+enum {
+	OPT_HELP = 1,
+	OPT_DISCARD,
+	OPT_OVERWRITE,
+	OPT_SUBBUF_SIZE,
+	OPT_NUM_SUBBUF,
+	OPT_SWITCH_TIMER,
+	OPT_MONITOR_TIMER,
+	OPT_READ_TIMER,
+	OPT_USERSPACE,
+	OPT_LIST_OPTIONS,
+	OPT_TRACEFILE_SIZE,
+	OPT_TRACEFILE_COUNT,
+	OPT_BLOCKING_TIMEOUT,
+};
+
+static struct lttng_handle *handle;
+
+const char *output_mmap = "mmap";
+const char *output_splice = "splice";
+
+static struct poptOption long_options[] = {
+	/* longName, shortName, argInfo, argPtr, value, descrip, argDesc */
+	{"help",           'h', POPT_ARG_NONE, 0, OPT_HELP, 0, 0},
+	{"session",        's', POPT_ARG_STRING, &opt_session_name, 0, 0, 0},
+	{"kernel",         'k', POPT_ARG_VAL, &opt_kernel, 1, 0, 0},
+	{"userspace",      'u', POPT_ARG_NONE, 0, OPT_USERSPACE, 0, 0},
+	{"discard",        0,   POPT_ARG_NONE, 0, OPT_DISCARD, 0, 0},
+	{"overwrite",      0,   POPT_ARG_NONE, 0, OPT_OVERWRITE, 0, 0},
+	{"subbuf-size",    0,   POPT_ARG_STRING, 0, OPT_SUBBUF_SIZE, 0, 0},
+	{"num-subbuf",     0,   POPT_ARG_INT, 0, OPT_NUM_SUBBUF, 0, 0},
+	{"switch-timer",   0,   POPT_ARG_INT, 0, OPT_SWITCH_TIMER, 0, 0},
+	{"monitor-timer",  0,   POPT_ARG_INT, 0, OPT_MONITOR_TIMER, 0, 0},
+	{"read-timer",     0,   POPT_ARG_INT, 0, OPT_READ_TIMER, 0, 0},
+	{"list-options",   0, POPT_ARG_NONE, NULL, OPT_LIST_OPTIONS, NULL, NULL},
+	{"output",         0,   POPT_ARG_STRING, &opt_output, 0, 0, 0},
+	{"buffers-uid",    0,	POPT_ARG_VAL, &opt_buffer_uid, 1, 0, 0},
+	{"buffers-pid",    0,	POPT_ARG_VAL, &opt_buffer_pid, 1, 0, 0},
+	{"buffers-global", 0,	POPT_ARG_VAL, &opt_buffer_global, 1, 0, 0},
+	{"tracefile-size", 'C',   POPT_ARG_INT, 0, OPT_TRACEFILE_SIZE, 0, 0},
+	{"tracefile-count", 'W',   POPT_ARG_INT, 0, OPT_TRACEFILE_COUNT, 0, 0},
+	{"blocking-timeout",     0,   POPT_ARG_INT, 0, OPT_BLOCKING_TIMEOUT, 0, 0},
+	{0, 0, 0, 0, 0, 0, 0}
+};
+
+/*
+ * Set default attributes depending on those already defined from the command
+ * line.
+ */
+static void set_default_attr(struct lttng_domain *dom)
+{
+	struct lttng_channel_attr default_attr;
+
+	memset(&default_attr, 0, sizeof(default_attr));
+
+	/* Set attributes */
+	lttng_channel_set_default_attr(dom, &default_attr);
+
+	if (chan_opts.attr.overwrite == -1) {
+		chan_opts.attr.overwrite = default_attr.overwrite;
+	}
+	if (chan_opts.attr.subbuf_size == -1) {
+		chan_opts.attr.subbuf_size = default_attr.subbuf_size;
+	}
+	if (chan_opts.attr.num_subbuf == -1) {
+		chan_opts.attr.num_subbuf = default_attr.num_subbuf;
+	}
+	if (chan_opts.attr.switch_timer_interval == -1) {
+		chan_opts.attr.switch_timer_interval = default_attr.switch_timer_interval;
+	}
+	if (chan_opts.attr.read_timer_interval == -1) {
+		chan_opts.attr.read_timer_interval = default_attr.read_timer_interval;
+	}
+	if ((int) chan_opts.attr.output == -1) {
+		chan_opts.attr.output = default_attr.output;
+	}
+	if (chan_opts.attr.tracefile_count == -1) {
+		chan_opts.attr.tracefile_count = default_attr.tracefile_count;
+	}
+	if (chan_opts.attr.tracefile_size == -1) {
+		chan_opts.attr.tracefile_size = default_attr.tracefile_size;
+	}
+}
+
+/*
+ * Adding channel using the lttng API.
+ */
+static int enable_channel(char *session_name)
+{
+	struct lttng_channel *channel = NULL;
+	int ret = CMD_SUCCESS, warn = 0, error = 0, success = 0;
+	char *channel_name;
+	struct lttng_domain dom;
+
+	memset(&dom, 0, sizeof(dom));
+
+	/* Validate options. */
+	if (opt_kernel) {
+		if (opt_blocking_timeout.set) {
+			ERR("Retry timeout option not supported for kernel domain (-k)");
+			ret = CMD_ERROR;
+			goto error;
+		}
+	}
+
+	/* Create lttng domain */
+	if (opt_kernel) {
+		dom.type = LTTNG_DOMAIN_KERNEL;
+		dom.buf_type = LTTNG_BUFFER_GLOBAL;
+		if (opt_buffer_uid || opt_buffer_pid) {
+			ERR("Buffer type not supported for domain -k");
+			ret = CMD_ERROR;
+			goto error;
+		}
+	} else if (opt_userspace) {
+		dom.type = LTTNG_DOMAIN_UST;
+		if (opt_buffer_pid) {
+			dom.buf_type = LTTNG_BUFFER_PER_PID;
+		} else {
+			if (opt_buffer_global) {
+				ERR("Buffer type not supported for domain -u");
+				ret = CMD_ERROR;
+				goto error;
+			}
+			dom.buf_type = LTTNG_BUFFER_PER_UID;
+		}
+	} else {
+		/* Checked by the caller. */
+		abort();
+	}
+
+	set_default_attr(&dom);
+
+	if (chan_opts.attr.tracefile_size == 0 && chan_opts.attr.tracefile_count) {
+		ERR("Missing option --tracefile-size. "
+				"A file count without a size won't do anything.");
+		ret = CMD_ERROR;
+		goto error;
+	}
+
+	if ((chan_opts.attr.tracefile_size > 0) &&
+			(chan_opts.attr.tracefile_size < chan_opts.attr.subbuf_size)) {
+		WARN("Tracefile size rounded up from (%" PRIu64 ") to subbuffer size (%" PRIu64 ")",
+				chan_opts.attr.tracefile_size, chan_opts.attr.subbuf_size);
+		chan_opts.attr.tracefile_size = chan_opts.attr.subbuf_size;
+	}
+
+	/* Setting channel output */
+	if (opt_output) {
+		if (!strncmp(output_mmap, opt_output, strlen(output_mmap))) {
+			chan_opts.attr.output = LTTNG_EVENT_MMAP;
+		} else if (!strncmp(output_splice, opt_output, strlen(output_splice))) {
+			chan_opts.attr.output = LTTNG_EVENT_SPLICE;
+		} else {
+			ERR("Unknown output type %s. Possible values are: %s, %s\n",
+					opt_output, output_mmap, output_splice);
+			ret = CMD_ERROR;
+			goto error;
+		}
+	}
+
+	handle = lttng_create_handle(session_name, &dom);
+	if (handle == NULL) {
+		ret = -1;
+		goto error;
+	}
+
+	/* Mi open channels element */
+	if (lttng_opt_mi) {
+		LTTNG_ASSERT(writer);
+		ret = mi_lttng_channels_open(writer);
+		if (ret) {
+			ret = CMD_ERROR;
+			goto error;
+		}
+	}
+
+	/* Strip channel list (format: chan1,chan2,...) */
+	channel_name = strtok(opt_channels, ",");
+	while (channel_name != NULL) {
+		void *extended_ptr;
+
+		/* Validate channel name's length */
+		if (strlen(channel_name) >= sizeof(chan_opts.name)) {
+			ERR("Channel name is too long (max. %zu characters)",
+					sizeof(chan_opts.name) - 1);
+			error = 1;
+			goto skip_enable;
+		}
+
+		/*
+		 * A dynamically-allocated channel is used in order to allow
+		 * the configuration of extended attributes (post-2.9).
+		 */
+		channel = lttng_channel_create(&dom);
+		if (!channel) {
+			ERR("Unable to create channel object");
+			error = 1;
+			goto error;
+		}
+
+		/* Copy channel name */
+		strcpy(channel->name, channel_name);
+		channel->enabled = 1;
+		extended_ptr = channel->attr.extended.ptr;
+		memcpy(&channel->attr, &chan_opts.attr, sizeof(chan_opts.attr));
+		channel->attr.extended.ptr = extended_ptr;
+		if (opt_monitor_timer.set) {
+			ret = lttng_channel_set_monitor_timer_interval(channel,
+					opt_monitor_timer.interval);
+			if (ret) {
+				ERR("Failed to set the channel's monitor timer interval");
+				error = 1;
+				goto error;
+			}
+		}
+		if (opt_blocking_timeout.set) {
+			ret = lttng_channel_set_blocking_timeout(channel,
+					opt_blocking_timeout.value);
+			if (ret) {
+				ERR("Failed to set the channel's blocking timeout");
+				error = 1;
+				goto error;
+			}
+		}
+
+		DBG("Enabling channel %s", channel_name);
+
+		ret = lttng_enable_channel(handle, channel);
+		if (ret < 0) {
+			success = 0;
+			switch (-ret) {
+			case LTTNG_ERR_KERN_CHAN_EXIST:
+			case LTTNG_ERR_UST_CHAN_EXIST:
+			case LTTNG_ERR_CHAN_EXIST:
+				WARN("Channel %s: %s (session %s)", channel_name,
+						lttng_strerror(ret), session_name);
+				warn = 1;
+				break;
+			case LTTNG_ERR_INVALID_CHANNEL_NAME:
+				ERR("Invalid channel name: \"%s\". "
+				    "Channel names may not start with '.', and "
+				    "may not contain '/'.", channel_name);
+				error = 1;
+				break;
+			default:
+				ERR("Channel %s: %s (session %s)", channel_name,
+						lttng_strerror(ret), session_name);
+				error = 1;
+				break;
+			}
+		} else {
+			MSG("%s channel %s enabled for session %s",
+					lttng_domain_type_str(dom.type),
+					channel_name, session_name);
+			success = 1;
+		}
+
+skip_enable:
+		if (lttng_opt_mi) {
+			/* Mi print the channel element and leave it open */
+			ret = mi_lttng_channel(writer, channel, 1);
+			if (ret) {
+				ret = CMD_ERROR;
+				goto error;
+			}
+
+			/* Individual Success ? */
+			ret = mi_lttng_writer_write_element_bool(writer,
+					mi_lttng_element_command_success, success);
+			if (ret) {
+				ret = CMD_ERROR;
+				goto error;
+			}
+
+			/* Close channel element */
+			ret = mi_lttng_writer_close_element(writer);
+			if (ret) {
+				ret = CMD_ERROR;
+				goto error;
+			}
+		}
+
+		/* Next channel */
+		channel_name = strtok(NULL, ",");
+		lttng_channel_destroy(channel);
+		channel = NULL;
+	}
+
+	if (lttng_opt_mi) {
+		/* Close channels element */
+		ret = mi_lttng_writer_close_element(writer);
+		if (ret) {
+			ret = CMD_ERROR;
+			goto error;
+		}
+	}
+
+	ret = CMD_SUCCESS;
+
+error:
+	if (channel) {
+		lttng_channel_destroy(channel);
+	}
+	/* If more important error happen bypass the warning */
+	if (!ret && warn) {
+		ret = CMD_WARNING;
+	}
+	/* If more important error happen bypass the warning */
+	if (!ret && error) {
+		ret = CMD_ERROR;
+	}
+
+	lttng_destroy_handle(handle);
+
+	return ret;
+}
+
+/*
+ * Default value for channel configuration.
+ */
+static void init_channel_config(void)
+{
+	/*
+	 * Put -1 everywhere so we can identify those set by the command line and
+	 * those needed to be set by the default values.
+	 */
+	memset(&chan_opts.attr, -1, sizeof(chan_opts.attr));
+	chan_opts.attr.extended.ptr = NULL;
+}
+
+/*
+ * Add channel to trace session
+ */
+int cmd_enable_channels(int argc, const char **argv)
+{
+	int opt, ret = CMD_SUCCESS, command_ret = CMD_SUCCESS, success = 1;
+	static poptContext pc;
+	char *session_name = NULL;
+	char *opt_arg = NULL;
+	const char *leftover = NULL;
+
+	init_channel_config();
+
+	pc = poptGetContext(NULL, argc, argv, long_options, 0);
+	poptReadDefaultConfig(pc, 0);
+
+	while ((opt = poptGetNextOpt(pc)) != -1) {
+		switch (opt) {
+		case OPT_HELP:
+			SHOW_HELP();
+			goto end;
+		case OPT_DISCARD:
+			chan_opts.attr.overwrite = 0;
+			DBG("Channel set to discard");
+			break;
+		case OPT_OVERWRITE:
+			chan_opts.attr.overwrite = 1;
+			DBG("Channel set to overwrite");
+			break;
+		case OPT_SUBBUF_SIZE:
+		{
+			uint64_t rounded_size;
+			int order;
+
+			/* Parse the size */
+			opt_arg = poptGetOptArg(pc);
+			if (utils_parse_size_suffix(opt_arg, &chan_opts.attr.subbuf_size) < 0 || !chan_opts.attr.subbuf_size) {
+				ERR("Wrong value in --subbuf-size parameter: %s", opt_arg);
+				ret = CMD_ERROR;
+				goto end;
+			}
+
+			order = get_count_order_u64(chan_opts.attr.subbuf_size);
+			LTTNG_ASSERT(order >= 0);
+			rounded_size = 1ULL << order;
+			if (rounded_size < chan_opts.attr.subbuf_size) {
+				ERR("The subbuf size (%" PRIu64 ") is rounded and overflows!",
+						chan_opts.attr.subbuf_size);
+				ret = CMD_ERROR;
+				goto end;
+			}
+
+			if (rounded_size != chan_opts.attr.subbuf_size) {
+				WARN("The subbuf size (%" PRIu64 ") is rounded to the next power of 2 (%" PRIu64 ")",
+						chan_opts.attr.subbuf_size, rounded_size);
+				chan_opts.attr.subbuf_size = rounded_size;
+			}
+
+			/* Should now be power of 2 */
+			LTTNG_ASSERT(!((chan_opts.attr.subbuf_size - 1) & chan_opts.attr.subbuf_size));
+
+			DBG("Channel subbuf size set to %" PRIu64, chan_opts.attr.subbuf_size);
+			break;
+		}
+		case OPT_NUM_SUBBUF:
+		{
+			uint64_t rounded_size;
+			int order;
+
+			errno = 0;
+			opt_arg = poptGetOptArg(pc);
+			chan_opts.attr.num_subbuf = strtoull(opt_arg, NULL, 0);
+			if (errno != 0 || !chan_opts.attr.num_subbuf || !isdigit(opt_arg[0])) {
+				ERR("Wrong value in --num-subbuf parameter: %s", opt_arg);
+				ret = CMD_ERROR;
+				goto end;
+			}
+
+			order = get_count_order_u64(chan_opts.attr.num_subbuf);
+			LTTNG_ASSERT(order >= 0);
+			rounded_size = 1ULL << order;
+			if (rounded_size < chan_opts.attr.num_subbuf) {
+				ERR("The number of subbuffers (%" PRIu64 ") is rounded and overflows!",
+						chan_opts.attr.num_subbuf);
+				ret = CMD_ERROR;
+				goto end;
+			}
+
+			if (rounded_size != chan_opts.attr.num_subbuf) {
+				WARN("The number of subbuffers (%" PRIu64 ") is rounded to the next power of 2 (%" PRIu64 ")",
+						chan_opts.attr.num_subbuf, rounded_size);
+				chan_opts.attr.num_subbuf = rounded_size;
+			}
+
+			/* Should now be power of 2 */
+			LTTNG_ASSERT(!((chan_opts.attr.num_subbuf - 1) & chan_opts.attr.num_subbuf));
+
+			DBG("Channel subbuf num set to %" PRIu64, chan_opts.attr.num_subbuf);
+			break;
+		}
+		case OPT_SWITCH_TIMER:
+		{
+			uint64_t v;
+
+			errno = 0;
+			opt_arg = poptGetOptArg(pc);
+
+			if (utils_parse_time_suffix(opt_arg, &v) < 0) {
+				ERR("Wrong value for --switch-timer parameter: %s", opt_arg);
+				ret = CMD_ERROR;
+				goto end;
+			}
+
+			if (v != (uint32_t) v) {
+				ERR("32-bit overflow in --switch-timer parameter: %s", opt_arg);
+				ret = CMD_ERROR;
+				goto end;
+			}
+			chan_opts.attr.switch_timer_interval = (uint32_t) v;
+			DBG("Channel switch timer interval set to %d %s",
+					chan_opts.attr.switch_timer_interval,
+					USEC_UNIT);
+			break;
+		}
+		case OPT_READ_TIMER:
+		{
+			uint64_t v;
+
+			errno = 0;
+			opt_arg = poptGetOptArg(pc);
+
+			if (utils_parse_time_suffix(opt_arg, &v) < 0) {
+				ERR("Wrong value for --read-timer parameter: %s", opt_arg);
+				ret = CMD_ERROR;
+				goto end;
+			}
+
+			if (v != (uint32_t) v) {
+				ERR("32-bit overflow in --read-timer parameter: %s", opt_arg);
+				ret = CMD_ERROR;
+				goto end;
+			}
+			chan_opts.attr.read_timer_interval = (uint32_t) v;
+			DBG("Channel read timer interval set to %d %s",
+					chan_opts.attr.read_timer_interval,
+					USEC_UNIT);
+			break;
+		}
+		case OPT_MONITOR_TIMER:
+		{
+			uint64_t v;
+
+			errno = 0;
+			opt_arg = poptGetOptArg(pc);
+
+			if (utils_parse_time_suffix(opt_arg, &v) < 0) {
+				ERR("Wrong value for --monitor-timer parameter: %s", opt_arg);
+				ret = CMD_ERROR;
+				goto end;
+			}
+			opt_monitor_timer.interval = (uint64_t) v;
+			opt_monitor_timer.set = true;
+			DBG("Channel monitor timer interval set to %" PRIu64 " %s",
+					opt_monitor_timer.interval,
+					USEC_UNIT);
+			break;
+		}
+		case OPT_BLOCKING_TIMEOUT:
+		{
+			uint64_t v;
+			long long v_msec;
+
+			errno = 0;
+			opt_arg = poptGetOptArg(pc);
+
+			if (strcmp(opt_arg, "inf") == 0) {
+				opt_blocking_timeout.value = (int64_t) -1;
+				opt_blocking_timeout.set = true;
+				DBG("Channel blocking timeout set to infinity");
+				break;
+			}
+
+			if (utils_parse_time_suffix(opt_arg, &v) < 0) {
+				ERR("Wrong value for --blocking-timeout parameter: %s", opt_arg);
+				ret = CMD_ERROR;
+				goto end;
+			}
+
+			/*
+			 * While LTTng-UST and LTTng-tools will accept a
+			 * blocking timeout expressed in µs, the current
+			 * tracer implementation relies on poll() which
+			 * takes an "int timeout" parameter expressed in
+			 * msec.
+			 *
+			 * Since the error reporting from the tracer is
+			 * not precise, we perform this check here to
+			 * provide a helpful error message in case of
+			 * overflow.
+			 *
+			 * The setter (liblttng-ctl) also performs an
+			 * equivalent check.
+			 */
+			v_msec = v / 1000;
+			if (v_msec != (int32_t) v_msec) {
+				ERR("32-bit milliseconds overflow in --blocking-timeout parameter: %s", opt_arg);
+				ret = CMD_ERROR;
+				goto end;
+			}
+
+			opt_blocking_timeout.value = (int64_t) v;
+			opt_blocking_timeout.set = true;
+			DBG("Channel blocking timeout set to %" PRId64 " %s%s",
+					opt_blocking_timeout.value,
+					USEC_UNIT,
+					opt_blocking_timeout.value == 0 ?
+						" (non-blocking)" : "");
+			break;
+		}
+		case OPT_USERSPACE:
+			opt_userspace = 1;
+			break;
+		case OPT_TRACEFILE_SIZE:
+			opt_arg = poptGetOptArg(pc);
+			if (utils_parse_size_suffix(opt_arg, &chan_opts.attr.tracefile_size) < 0) {
+				ERR("Wrong value in --tracefile-size parameter: %s", opt_arg);
+				ret = CMD_ERROR;
+				goto end;
+			}
+			DBG("Maximum tracefile size set to %" PRIu64,
+					chan_opts.attr.tracefile_size);
+			break;
+		case OPT_TRACEFILE_COUNT:
+		{
+			unsigned long v;
+
+			errno = 0;
+			opt_arg = poptGetOptArg(pc);
+			v = strtoul(opt_arg, NULL, 0);
+			if (errno != 0 || !isdigit(opt_arg[0])) {
+				ERR("Wrong value in --tracefile-count parameter: %s", opt_arg);
+				ret = CMD_ERROR;
+				goto end;
+			}
+			if (v != (uint32_t) v) {
+				ERR("32-bit overflow in --tracefile-count parameter: %s", opt_arg);
+				ret = CMD_ERROR;
+				goto end;
+			}
+			chan_opts.attr.tracefile_count = (uint32_t) v;
+			DBG("Maximum tracefile count set to %" PRIu64,
+					chan_opts.attr.tracefile_count);
+			break;
+		}
+		case OPT_LIST_OPTIONS:
+			list_cmd_options(stdout, long_options);
+			goto end;
+		default:
+			ret = CMD_UNDEFINED;
+			goto end;
+		}
+	}
+
+	ret = print_missing_or_multiple_domains(
+			opt_kernel + opt_userspace, false);
+	if (ret) {
+		ret = CMD_ERROR;
+		goto end;
+	}
+
+	if (chan_opts.attr.overwrite == 1 && opt_blocking_timeout.set &&
+			opt_blocking_timeout.value != 0) {
+		ERR("You cannot specify --overwrite and --blocking-timeout=N, "
+			"where N is different than 0");
+		ret = CMD_ERROR;
+		goto end;
+	}
+
+	/* Mi check */
+	if (lttng_opt_mi) {
+		writer = mi_lttng_writer_create(fileno(stdout), lttng_opt_mi);
+		if (!writer) {
+			ret = -LTTNG_ERR_NOMEM;
+			goto end;
+		}
+
+		/* Open command element */
+		ret = mi_lttng_writer_command_open(writer,
+				mi_lttng_element_command_enable_channels);
+		if (ret) {
+			ret = CMD_ERROR;
+			goto end;
+		}
+
+		/* Open output element */
+		ret = mi_lttng_writer_open_element(writer,
+				mi_lttng_element_command_output);
+		if (ret) {
+			ret = CMD_ERROR;
+			goto end;
+		}
+	}
+
+	opt_channels = (char*) poptGetArg(pc);
+	if (opt_channels == NULL) {
+		ERR("Missing channel name.\n");
+		ret = CMD_ERROR;
+		success = 0;
+		goto mi_closing;
+	}
+
+	leftover = poptGetArg(pc);
+	if (leftover) {
+		ERR("Unknown argument: %s", leftover);
+		ret = CMD_ERROR;
+		success = 0;
+		goto mi_closing;
+	}
+
+	if (!opt_session_name) {
+		session_name = get_session_name();
+		if (session_name == NULL) {
+			command_ret = CMD_ERROR;
+			success = 0;
+			goto mi_closing;
+		}
+	} else {
+		session_name = opt_session_name;
+	}
+
+	command_ret = enable_channel(session_name);
+	if (command_ret) {
+		success = 0;
+	}
+
+mi_closing:
+	/* Mi closing */
+	if (lttng_opt_mi) {
+		/* Close  output element */
+		ret = mi_lttng_writer_close_element(writer);
+		if (ret) {
+			goto end;
+		}
+
+		/* Success ? */
+		ret = mi_lttng_writer_write_element_bool(writer,
+				mi_lttng_element_command_success, success);
+		if (ret) {
+			goto end;
+		}
+
+		/* Command element close */
+		ret = mi_lttng_writer_command_close(writer);
+		if (ret) {
+			goto end;
+		}
+	}
+
+end:
+	/* Mi clean-up */
+	if (writer && mi_lttng_writer_destroy(writer)) {
+		/* Preserve original error code */
+		ret = ret ? ret : LTTNG_ERR_MI_IO_FAIL;
+	}
+
+	if (!opt_session_name && session_name) {
+		free(session_name);
+	}
+
+	/* Overwrite ret if an error occurred when enable_channel */
+	ret = command_ret ? command_ret : ret;
+	poptFreeContext(pc);
+	return ret;
+}