Trace - Provides tracing primitives Tom Zanussi Martin Hunt David Wilder --- Documentation/trace.txt | 297 ++++++++++++++++++++++++ include/linux/trace.h | 99 ++++++++ lib/Kconfig | 10 + lib/Makefile | 2 + lib/trace.c | 575 +++++++++++++++++++++++++++++++++++++++++++++++ 5 files changed, 983 insertions(+), 0 deletions(-) diff --git a/Documentation/trace.txt b/Documentation/trace.txt new file mode 100644 index 0000000..57a5c71 --- /dev/null +++ b/Documentation/trace.txt @@ -0,0 +1,297 @@ +Trace Setup and Control +======================= +In the kernel, the trace interface provides a simple mechanism for +starting and managing data channels (traces) to user space. The +trace interface builds on the relay interface. For a complete +description of the relay interface, please see: +Documentation/filesystems/relay.txt. + +The trace interface provides a single layer in a complete tracing +application. Trace provides a kernel API that can be used for the setup +and control of tracing channels. User of trace must provide a data layer +responsible for formatting and writing data into the trace channels. + +A layered approach to tracing +============================= +A complete kernel tracing application consists of a data provider and +a data consumer. Both provider and consumer contain three layers; each +layer works in tandem with the corresponding layer in the opposite side. +The layers are represented in the following diagram. + +Provider Data layer + Formats raw trace data and provides data-related service. + For example, adding timestamps used by consumer to sort data. + +Provider Control layer + Provided by the trace interface, this layer creates trace channels + and informs the data layer and consumer of the current state + of the trace channels. + +Provider Buffering layer + Provided by relay. This layer buffers data in the + kernel for consumption by the consumer's buffer + layer. + +Provider (in-kernel facility) +----------------------------------------------------------------------------- +Consumer (user application) + + +Consumer Buffer layer + Reads/consumes data from the provider's data buffers. + +Consumer Control layer + Communicates to the provider's control layer to control the state + of the trace channels. + +Consumer Data layer + Sorts and formats data as provided by the provider's data layer. + +The provider is coded as a kernel facility. The consumer is coded as +a user application. + + +Trace - Features +================ +Trace exploits services and features provided by relay. These features +are: +- The creation and destruction of relay channels. +- Buffer management. Overwrite or non-overwrite modes can be selected + as well as global or per-CPU buffering. + +Overwrite mode can be called "flight recorder mode". Flight recorder +mode is selected by setting the TRACE_FLIGHT_CHANNEL flag when +creating trace channels. In flight mode when a tracing buffer is +full, the oldest records in the buffer will be discarded to make room +as new records arrive. In the default non-overwrite mode, new records +may be written only if the buffer has room. In either case, to +prevent data loss, a user space reader must keep the buffers +drained. Trace provides a means to detect the number of records that +have been dropped due to a buffer-full condition (non-overwrite mode +only). + +When per-CPU buffers are used, relay creates one debugfs file for each +running CPU. The user-space consumer of the data is responsible for +reading the per-CPU buffers and collating the records presumably using +a time stamp or sequence number included in the trace records. The +use of global buffers eliminates this extra work of sequencing +records; however the provider's data layer must hold a lock when +writing records. The lock prevents writers running on different CPUs +from overwriting each other's data. However, buffering may be slower +because writes to the buffer are serialized. Global buffering is +selected by setting the TRACE_GLOBAL_CHANNEL flag when creating trace +channels. + +Trace User Interface +=================== +When a trace channel is created and started, the following +directories and files are created in the root of the mounted debugfs. + +/debug (root of the debugfs) + / + / + trace0 ... traceN Per-CPU trace data, one + file per CPU. + + state Start or stop tracing by + by writing the strings + "start" or "stop" to this + file. Read the file to get the + current state. + + dropped The number of records dropped + due to a full-buffer condition, + for non-TRACE_FLIGHT_CHANNELs + only. + + rewind Trigger a rewind by writing + to this file. i.e. start + next read at the beginning + again. Only available for + TRACE_FLIGHT_CHANNELS. + + + nr_sub Number of sub-buffers + in the channel. + + sub_size Size of sub-buffers in + the channnel. + +Trace data is gathered from the trace[0...N] files using one of the +available interfaces provided by relay. + +When using the READ(2) interface, as data is read it is marked as +consumed by the relay subsystem. Therefore, subsequent reads will +only return unconsumed data. + +Trace Kernel API +=============== +An overview of the trace Kernel API is now given. More details of the +API can be found in linux/trace.h. + +The steps a kernel data provider takes to utilize the trace interface are: +1) Set up a trace channel - trace_setup() +2) Start the trace channel - trace_start() +3) Write one or more trace records into the channel (using the relay API). + + Important: When writing a trace record the provider must insure that + preemption is disabled and that trace state is set to "running". a + typical function used to write records into a trace channel should + follow the following semantics: + + rcu_read_lock(); // disables preemption + if (trace_running(trace)){ + relay_write(....); // use any available relay data + function + } + rcu_read_unlock(); // enables preemption + +4) Stop and start tracing as desired - trace_start()/trace_stop() +5) Destroy the trace channel and underlying relay channel - +trace_cleanup(). + +Trace Example +=========== + +This small sample module creates a trace channel. It places a kprobe +on the function do_fork(). The value of current->pid is writen to +the trace channel. + +You can build the kernel module fork_trace.ko using the following +Makefile: +------------------------------------CUT------------------------------------- +obj-m := fork_trace.o +KDIR := /lib/modules/$(shell uname -r)/build +PWD := $(shell pwd) +default: + $(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules +clean: + rm -f *.mod.c *.ko *.o +----------------------------------CUT-------------------------------------- + +/* fork_trace.c - An example of using trace in a kprobes module */ +#include +#include +#include +#include + +#define USE_GLOBAL_BUFFERS 1 +#define USE_FLIGHT 1 + +#define PROBE_POINT "do_fork" + +static struct kprobe kp; +struct trace_info *kprobes_trace; + +#ifdef USE_GLOBAL_BUFFERS +static DEFINE_SPINLOCK(trace_lock); +#endif + +#define TRACE_PRINTF_TMPBUF_SIZE (1024) +static char trace_tmpbuf[NR_CPUS][TRACE_PRINTF_TMPBUF_SIZE]; + +void trace_printf(struct trace_info *trace, const char *format, ...) +{ + va_list args; + void *buf; + char *record; + int len=0; + + if (!trace) + return; + + buf = trace_tmpbuf[smp_processor_id()]; + +#ifdef USE_GLOBAL_BUFFERS + spin_lock(&trace_lock); +#endif + + rcu_read_lock(); + if (trace_running(trace)){ + va_start(args, format); + len += vsnprintf(buf+len, TRACE_PRINTF_TMPBUF_SIZE, + format, args); + va_end(args); + + if ((record = relay_reserve(trace->rchan, len))) + memcpy(record, buf, len); + } + rcu_read_unlock(); + +#ifdef USE_GLOBAL_BUFFERS + spin_unlock(&trace_lock); +#endif +} + + +int handler_pre(struct kprobe *p, struct pt_regs *regs) +{ + trace_printf(kprobes_trace,"%d\n", current->pid); + return 0; +} + + +int init_module(void) +{ + u32 flags=0; + +#ifdef USE_GLOBAL_BUFFERS + flags |= TRACE_GLOBAL_CHANNEL; +#endif + +#ifdef USE_FLIGHT + flags |= TRACE_FLIGHT_CHANNEL; +#endif + + /* setup the trace */ + kprobes_trace = trace_setup("trace_example",PROBE_POINT, + 1024,8,flags); + if (!kprobes_trace) + return -1; + + trace_start(kprobes_trace); + + /* setup the kprobe */ + kp.pre_handler = handler_pre; + kp.post_handler = NULL; + kp.fault_handler = NULL; + kp.symbol_name = PROBE_POINT; + if (register_kprobe(&kp) < 0) { + printk("fork_trace: register_kprobe failed\n"); + return -1; + } + return 0; +} + +void cleanup_module(void) +{ + unregister_kprobe(&kp); + trace_stop(kprobes_trace); + trace_cleanup(kprobes_trace); +} + +MODULE_LICENSE("GPL"); +-----------------------------CUT----------------------------------- +How to run the example: +$ mount -t debugfs /debug +$ make +$ insmod fork_trace.ko + +To view the data produced by the module: +$ cat /debug/trace_example/do_fork/trace0 + +Remove the module. +$ rmmod fork_trace + +The function trace_cleanup() is called when the module +is removed. This will cause the TRACE channel to be destroyed and the +corresponding files to disappear from the debug file system. + +Credits +======= +Trace is adapted from blktrace authored by Jens Axboe (axboe@suse.de). + +Major contributions were made by: +Tom Zanussi +Martin Hunt +David Wilder diff --git a/include/linux/trace.h b/include/linux/trace.h new file mode 100644 index 0000000..6dff7d0 --- /dev/null +++ b/include/linux/trace.h @@ -0,0 +1,99 @@ +/* + * TRACE defines and function prototypes + * + * Copyright (C) 2006 IBM Inc. + * + * Tom Zanussi + * Martin Hunt + * David Wilder + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + * + * This program 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 General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA + * + */ +#ifndef _LINUX_TRACE_H +#define _LINUX_TRACE_H + +#include + +/* + * TRACE channel flags + */ +#define TRACE_GLOBAL_CHANNEL 0x01 +#define TRACE_FLIGHT_CHANNEL 0x02 +#define TRACE_DISABLE_STATE 0x04 + +enum trace_state { + TRACE_SETUP, + TRACE_RUNNING, + TRACE_STOPPED, +}; + +#define TRACE_ROOT_NAME_SIZE 64 /* Max root dir identifier */ +#define TRACE_NAME_SIZE 64 /* Max trace identifier */ + +/* + * Global root user information + */ +struct trace_root { + struct list_head list; + char name[TRACE_ROOT_NAME_SIZE]; + struct dentry *root; + unsigned int users; +}; + +/* + * Client information + */ +struct trace_info { + struct mutex state_mutex; + enum trace_state state; + struct dentry *state_file; + struct rchan *rchan; + struct dentry *dir; + struct dentry *dropped_file; + struct dentry *reset_consumed_file; + struct dentry *nr_sub_file; + struct dentry *sub_size_file; + atomic_t dropped; + struct trace_root *root; + void *private_data; + unsigned int flags; + unsigned int buf_size; + unsigned int buf_nr; +}; + +#ifdef CONFIG_TRACE +static inline int trace_running(struct trace_info *trace) +{ + return trace->state == TRACE_RUNNING; +} +struct trace_info *trace_setup(const char *root, const char *name, + u32 buf_size, u32 buf_nr, u32 flags); +int trace_start(struct trace_info *trace); +int trace_stop(struct trace_info *trace); +void trace_cleanup(struct trace_info *trace); +#else +static inline struct trace_info *trace_setup(const char *root, + const char *name,u32 buf_size, + u32 buf_nr, u32 flags) +{ + return NULL; +} +static inline int trace_start(struct trace_info *trace) { return -EINVAL; } +static inline int trace_stop(struct trace_info *trace) { return -EINVAL; } +static inline int trace_running(struct trace_info *trace) { return 0; } +static inline void trace_cleanup(struct trace_info *trace) {} +#endif + +#endif diff --git a/lib/Kconfig b/lib/Kconfig index ba3d104..6d9fffa 100644 --- a/lib/Kconfig +++ b/lib/Kconfig @@ -141,4 +141,14 @@ config HAS_DMA config CHECK_SIGNATURE bool +config TRACE + bool "Trace setup and control" + select RELAY + select DEBUG_FS + help + This option provides support for the setup, teardown and control + of tracing channels from kernel code. It also provides trace + information and control to userspace via a set of debugfs control + files. If unsure, say N. + endmenu diff --git a/lib/Makefile b/lib/Makefile index 1e1e8c2..857d7af 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -69,6 +69,8 @@ lib-$(CONFIG_GENERIC_BUG) += bug.o obj-$(CONFIG_PROFILE_LIKELY) += likely_prof.o +obj-$(CONFIG_TRACE) += trace.o + hostprogs-y := gen_crc32table clean-files := crc32table.h diff --git a/lib/trace.c b/lib/trace.c new file mode 100644 index 0000000..17c9053 --- /dev/null +++ b/lib/trace.c @@ -0,0 +1,575 @@ +/* + * Based on blktrace code, Copyright (C) 2006 Jens Axboe + * Moved to utt.c by Tom Zanussi , 2006 + * Additional contributions by: + * Martin Hunt , 2007 + * David Wilder , 2007 + * Renamed to trace , 2007 + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + * + * This program 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 General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA + * + */ + +#include +#include +#include +#include +#include +#include + +static LIST_HEAD(trace_roots); +static DEFINE_MUTEX(trace_mutex); + +static int state_open(struct inode *inode, struct file *filp) +{ + filp->private_data = inode->i_private; + + return 0; +} + +static ssize_t state_read(struct file *filp, char __user *buffer, + size_t count, loff_t *ppos) +{ + struct trace_info *trace = filp->private_data; + char *buf = "trace not started\n"; + + if (trace->state == TRACE_STOPPED) + buf = "stopped\n"; + else if (trace->state == TRACE_RUNNING) + buf = "running\n"; + return simple_read_from_buffer(buffer, count, ppos, buf, strlen(buf)); +} + + +static ssize_t state_write(struct file *filp, const char __user *buffer, + size_t count, loff_t *ppos) +{ + struct trace_info *trace = filp->private_data; + char buf[16] = { '\0' }; + int ret; + + if (trace->flags & TRACE_DISABLE_STATE) + return -EINVAL; + + if (count > sizeof(buf) - 1) + return -EINVAL; + + if (copy_from_user(buf, buffer, count)) + return -EFAULT; + + buf[count] = '\0'; + + if (strncmp(buf, "start", strlen("start")) == 0 ) { + ret = trace_start(trace); + if (ret) + return ret; + } else if (strncmp(buffer, "stop", strlen("stop")) == 0) + trace_stop(trace); + else + return -EINVAL; + + return count; +} + + +static struct file_operations state_fops = { + .owner = THIS_MODULE, + .open = state_open, + .read = state_read, + .write = state_write, +}; + + +static void remove_root(struct trace_info *trace) +{ + if (trace->root->root && simple_empty(trace->root->root)) { + debugfs_remove(trace->root->root); + list_del(&trace->root->list); + kfree(trace->root); + trace->root = NULL; + } +} + + +static void remove_tree(struct trace_info *trace) +{ + mutex_lock(&trace_mutex); + + debugfs_remove(trace->dir); + + if (--trace->root->users == 0) + remove_root(trace); + + mutex_unlock(&trace_mutex); +} + + +/* + * Creates the trace_root if it's not found. + */ +static struct trace_root *lookup_root(const char *root) +{ + struct list_head *pos; + struct trace_root *r; + + list_for_each(pos, &trace_roots) { + r = list_entry(pos, struct trace_root, list); + if (!strcmp(r->name, root)) + return r; + } + + r = kzalloc(sizeof(struct trace_root), GFP_KERNEL); + if (!r) + return NULL; + + strlcpy(r->name, root, sizeof(r->name)); + + r->root = debugfs_create_dir(root, NULL); + if (r->root) + list_add(&r->list, &trace_roots); + + return r; +} + + +static struct dentry *create_tree(struct trace_info *trace, const char *root, + const char *name) +{ + struct dentry *dir = NULL; + + if (root == NULL || name == NULL) + return NULL; + + mutex_lock(&trace_mutex); + + trace->root = lookup_root(root); + if (!trace->root) + goto err; + + dir = debugfs_create_dir(name, trace->root->root); + if (dir) + trace->root->users++; + else + remove_root(trace); + +err: + mutex_unlock(&trace_mutex); + + return dir; +} + + +static int dropped_open(struct inode *inode, struct file *filp) +{ + filp->private_data = inode->i_private; + + return 0; +} + + +static ssize_t dropped_read(struct file *filp, char __user *buffer, + size_t count, loff_t *ppos) +{ + struct trace_info *trace = filp->private_data; + char buf[16]; + + snprintf(buf, sizeof(buf), "%u\n", atomic_read(&trace->dropped)); + + return simple_read_from_buffer(buffer, count, ppos, buf, strlen(buf)); +} + + +static struct file_operations dropped_fops = { + .owner = THIS_MODULE, + .open = dropped_open, + .read = dropped_read, +}; + +static int reset_consumed_open(struct inode *inode, struct file *filp) +{ + filp->private_data = inode->i_private; + + return 0; +} + +static ssize_t reset_consumed_write(struct file *filp, + const char __user *buffer, + size_t count, loff_t *ppos) +{ + int ret=count; + struct trace_info *trace = filp->private_data; + + mutex_lock(&trace->state_mutex); + switch (trace->state){ + case TRACE_RUNNING: + trace->state = TRACE_STOPPED; + synchronize_rcu(); + relay_flush(trace->rchan); + relay_reset_consumed(trace->rchan); + trace->state = TRACE_RUNNING; + break; + case TRACE_STOPPED: + relay_reset_consumed(trace->rchan); + break; + default: + ret = -EINVAL; + } + mutex_unlock(&trace->state_mutex); + return ret; +} + +struct file_operations reset_consumed_fops = { + .owner = THIS_MODULE, + .open = reset_consumed_open, + .write = reset_consumed_write +}; + +static int sub_size_open(struct inode *inode, struct file *filp) +{ + filp->private_data = inode->i_private; + + return 0; +} + +static ssize_t sub_size_read(struct file *filp, char __user *buffer, + size_t count, loff_t *ppos) +{ + struct trace_info *trace = filp->private_data; + char buf[32]; + + snprintf(buf, sizeof(buf), "%u\n", + (unsigned int)trace->rchan->subbuf_size); + + return simple_read_from_buffer(buffer, count, ppos, buf, strlen(buf)); +} + +struct file_operations sub_size_fops = { + .owner = THIS_MODULE, + .open = sub_size_open, + .read = sub_size_read, +}; + +static int nr_sub_open(struct inode *inode, struct file *filp) +{ + filp->private_data = inode->i_private; + return 0; +} + +static ssize_t nr_sub_read(struct file *filp, char __user *buffer, + size_t count, loff_t *ppos) +{ + struct trace_info *trace = filp->private_data; + char buf[32]; + + snprintf(buf, sizeof(buf), "%u\n", + (unsigned int)trace->rchan->n_subbufs); + + return simple_read_from_buffer(buffer, count, ppos, buf, strlen(buf)); +} + +struct file_operations nr_sub_fops = { + .owner = THIS_MODULE, + .open = nr_sub_open, + .read = nr_sub_read, +}; + +/* + * Keep track of how many times we encountered a full subbuffer, to aid + * the user space app in telling how many lost events there were. + */ +static int subbuf_start_callback(struct rchan_buf *buf, void *subbuf, + void *prev_subbuf, size_t prev_padding) +{ + struct trace_info *trace = buf->chan->private_data; + + if (trace->flags & TRACE_FLIGHT_CHANNEL) + return 1; + + if (!relay_buf_full(buf)) + return 1; + + atomic_inc(&trace->dropped); + + return 0; +} + + +static int remove_buf_file_callback(struct dentry *dentry) +{ + debugfs_remove(dentry); + + return 0; +} + + +static struct dentry *create_buf_file_callback(const char *filename, + struct dentry *parent, int mode, + struct rchan_buf *buf, + int *is_global) +{ + return debugfs_create_file(filename, mode, parent, buf, + &relay_file_operations); +} + + +static struct dentry *create_global_buf_file_callback(const char *filename, + struct dentry *parent, + int mode, + struct rchan_buf *buf, + int *is_global) +{ + *is_global = 1; + + return debugfs_create_file(filename, mode, parent, buf, + &relay_file_operations); +} + + +static struct rchan_callbacks relay_callbacks = { + .subbuf_start = subbuf_start_callback, + .create_buf_file = create_buf_file_callback, + .remove_buf_file = remove_buf_file_callback, +}; +static struct rchan_callbacks relay_callbacks_global = { + .subbuf_start = subbuf_start_callback, + .create_buf_file = create_global_buf_file_callback, + .remove_buf_file = remove_buf_file_callback, +}; + + +static void remove_controls(struct trace_info *trace) +{ + if (trace->state_file) + debugfs_remove(trace->state_file); + if (trace->dropped_file) + debugfs_remove(trace->dropped_file); + if (trace->reset_consumed_file) + debugfs_remove(trace->reset_consumed_file); + if (trace->nr_sub_file) + debugfs_remove(trace->nr_sub_file); + if (trace->sub_size_file) + debugfs_remove(trace->sub_size_file); + if (trace->dir) + remove_tree(trace); +} + +/* + * Setup controls for tracing. + */ +static struct trace_info *setup_controls(const char *root, + const char *name, u32 flags) +{ + struct trace_info *trace = NULL; + + trace = kzalloc(sizeof(*trace), GFP_KERNEL); + if (!trace) + goto err; + + trace->dir = create_tree(trace, root, name); + if (!trace->dir) + goto err; + + trace->state_file = debugfs_create_file("state", 0444, trace->dir, + trace, &state_fops); + if (!trace->state_file) + goto err; + + if (!flags & TRACE_FLIGHT_CHANNEL) { + trace->dropped_file = debugfs_create_file("dropped", 0444, + trace->dir, trace, + &dropped_fops); + if (!trace->dropped_file) + goto err; + } + + if (flags & TRACE_FLIGHT_CHANNEL) { + trace->reset_consumed_file = debugfs_create_file("rewind", + 0444, + trace->dir, + trace, + &reset_consumed_fops); + if (!trace->reset_consumed_file) + goto err; + } + + trace->nr_sub_file = debugfs_create_file("nr_sub", 0444, + trace->dir, trace, + &nr_sub_fops); + if (!trace->nr_sub_file) + goto err; + + trace->sub_size_file = debugfs_create_file("sub_size", 0444, + trace->dir, trace, + &sub_size_fops); + if (!trace->sub_size_file) + goto err; + + return trace; +err: + if (trace) { + remove_controls(trace); + kfree(trace); + } + + return NULL; +} + + +static int trace_setup_channel(struct trace_info *trace, u32 buf_size, + u32 buf_nr, u32 flags) +{ + if (!buf_size || !buf_nr) + return -EINVAL; + + if (flags & TRACE_GLOBAL_CHANNEL) + trace->rchan = relay_open("trace", trace->dir, buf_size, + buf_nr, &relay_callbacks_global, + trace); + else + trace->rchan = relay_open("trace", trace->dir, buf_size, + buf_nr, &relay_callbacks, trace); + + if (!trace->rchan) + return -ENOMEM; + + trace->flags = flags; + trace->state = TRACE_SETUP; + + return 0; +} + + +/** + * trace_setup: create a new trace trace handle + * + * @root: The root directory name in the root of the debugfs + * to place trace directories. Created as needed. + * @name: Trace directory name, created in @root + * @buf_size: size of the relay sub-buffers + * @buf_nr: number of relay sub-buffers + * @flags: Option selection (see GTSC channel flags definitions) + * default values when flags=0 are: use per-CPU buffering, + * use non-overwrite mode. See Documentation/trace.txt for details. + * + * returns a trace_info handle or NULL, if setup failed. + */ +struct trace_info *trace_setup(const char *root, const char *name, + u32 buf_size, u32 buf_nr, u32 flags) +{ + struct trace_info *trace = NULL; + + trace = setup_controls(root, name, flags); + if (!trace) + return NULL; + + trace->buf_size = buf_size; + trace->buf_nr = buf_nr; + trace->flags = flags; + mutex_init(&trace->state_mutex); + trace->state = TRACE_SETUP; + + return trace; +} +EXPORT_SYMBOL_GPL(trace_setup); + + +/** + * trace_start: start tracing + * + * @trace: trace handle to start. + * + * returns 0 if successful. + */ +int trace_start(struct trace_info *trace) +{ + /* + * For starting a trace, we can transition from a setup or stopped + * trace. + */ + if (trace->state == TRACE_RUNNING) + return -EINVAL; + + mutex_lock(&trace->state_mutex); + if (trace->state == TRACE_SETUP) { + int ret; + + ret = trace_setup_channel(trace, trace->buf_size, + trace->buf_nr, trace->flags); + if (ret){ + mutex_unlock(&trace->state_mutex); + return ret; + } + } + + trace->state = TRACE_RUNNING; + mutex_unlock(&trace->state_mutex); + + return 0; +} +EXPORT_SYMBOL_GPL(trace_start); + +/** + * trace_stop: stop tracing + * + * @trace: trace handle to stop. + * + */ +int trace_stop(struct trace_info *trace) +{ + int ret = -EINVAL; + + /* + * For stopping a trace, the state must be running + */ + mutex_lock(&trace->state_mutex); + if (trace->state == TRACE_RUNNING) { + trace->state = TRACE_STOPPED; + /* + * wait for all cpus to see the change in + * state before continuing + */ + synchronize_sched(); + relay_flush(trace->rchan); + ret = 0; + } + mutex_unlock(&trace->state_mutex); + return ret; +} +EXPORT_SYMBOL_GPL(trace_stop); + +/** + * trace_cleanup_channel: destroys the trace channel only + * + * @trace: trace handle to cleanup + */ +static void trace_cleanup_channel(struct trace_info *trace) +{ + trace_stop(trace); + if (trace->rchan) + relay_close(trace->rchan); + trace->rchan = NULL; +} + +/** + * trace_cleanup: destroys the trace channel, control files and dir + * + * @trace: trace handle to cleanup + */ +void trace_cleanup(struct trace_info *trace) +{ + trace_cleanup_channel(trace); + remove_controls(trace); + kfree(trace); +} +EXPORT_SYMBOL_GPL(trace_cleanup);