Date:	Mon, 19 May 2008 13:02:42 -0700
From:	David Wilder <dwilder@...ibm.com>
To:	"K.Prasad" <prasad@...ux.vnet.ibm.com>
CC:	kernel list <linux-kernel@...r.kernel.org>,
	akpm@...ux-foundation.org
Subject: Re: [RFC Patch 1/1] trace_printk and trace_dump interface - v2

ACK

trace_printk() and trace_dump() will be very usefully.  This simplified 
interface to trace is a needed improvement.  Among other features it 
makes it easy to convert from printk to trace and provides separate 
streams for debugging data.   For many subsystems a conversion from 
printk to trace only requires changing a #define.

Dave.

K.Prasad wrote:
> This patch introduces two new interfaces called trace_printk and
> trace_dump which can be used to print to the debugfs mount directly.
> It uses the 'trace' infrastructure underneath and is a patch over it.
> A sample file is also created to demonstrate its ease of use.
> 
> Signed-off-by: K.Prasad <prasad@...ux.vnet.ibm.com>
> ---
>  Documentation/trace.txt        |   22 ++++
>  include/linux/trace.h          |   57 +++++++++++
>  lib/trace.c                    |  204 
> +++++++++++++++++++++++++++++++++++++++--
>  samples/trace/Makefile         |    2
>  samples/trace/fork_new_trace.c |   99 +++++++++++++++++++
>  5 files changed, 378 insertions(+), 6 deletions(-)
> 
> Index: linux-blktrace-many/include/linux/trace.h
> ===================================================================
> --- linux-blktrace-many.orig/include/linux/trace.h
> +++ linux-blktrace-many/include/linux/trace.h
> @@ -39,10 +39,22 @@ enum trace_state {
>      TRACE_STOPPED,
>  };
> 
> +enum trace_dir_state {
> +    TRACE_PARENT_DIR_ABSENT,
> +    TRACE_PARENT_DIR_EXISTS,
> +    TRACE_DIR_EXISTS
> +};
> +
>  #define TRACE_ROOT_NAME_SIZE    64    /* Max root dir identifier */
>  #define TRACE_NAME_SIZE        64    /* Max trace identifier */
> 
>  /*
> + * Buffers for use by trace_printk
> + */
> +#define DEFAULT_TRACE_BUF_SIZE 4096
> +#define DEFAULT_TRACE_SUB_BUF_NR 40
> +
> +/*
>   * Global root user information
>   */
>  struct trace_root {
> @@ -71,6 +83,28 @@ struct trace_info {
>      unsigned int flags;
>      unsigned int buf_size;
>      unsigned int buf_nr;
> +    spinlock_t trace_lock;
> +};
> +
> +struct trace_printk_data {
> +    char *parent_dir;
> +    char *dir;
> +    int exists;
> +    int buf_size;
> +    int sub_buf_size;
> +    unsigned long flags;
> +    struct trace_info *ti;
> +};
> +
> +/*
> + * Information about every trace directory
> + */
> +struct trace_dir {
> +    struct list_head trace_dir_list;
> +    char trace_dir_name[TRACE_NAME_SIZE];
> +    struct dentry *trace_root;
> +    struct dentry *trace_dir;
> +    struct trace_info *ti;
>  };
> 
>  #ifdef CONFIG_TRACE
> @@ -83,6 +117,12 @@ struct trace_info *trace_setup(const cha
>  int trace_start(struct trace_info *trace);
>  int trace_stop(struct trace_info *trace);
>  void trace_cleanup(struct trace_info *trace);
> +int trace_exists(const char *parent_dir, const char *dir,
> +                    struct trace_info **ti);
> +void trace_cleanup_all(const char *parent_dir);
> +int trace_printk(struct trace_printk_data *dpk, char *format, ...);
> +int trace_dump(struct trace_printk_data *dpk, const void *output,
> +                            const int output_len);
>  #else
>  static inline struct trace_info *trace_setup(const char *root,
>                           const char *name, u32 buf_size,
> @@ -94,6 +134,23 @@ static inline int trace_start(struct tra
>  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) {}
> +static inline int trace_exists(const char *parent_dir, const char *dir,
> +                struct trace_info **ti)
> +{
> +    return -EINVAL;
> +}
> +static inline void trace_cleanup_all(const char *parent_dir) {}
> +static inline int trace_printk(struct trace_printk_data *dpk, char 
> *format,
> +                ...)
> +{
> +    return -EINVAL;
> +}
> +int trace_dump(struct trace_printk_data *dpk, const void *output,
> +                            const int output_len)
> +{
> +    return -EINVAL;
> +}
> +
>  #endif
> 
>  #endif
> Index: linux-blktrace-many/lib/trace.c
> ===================================================================
> --- linux-blktrace-many.orig/lib/trace.c
> +++ linux-blktrace-many/lib/trace.c
> @@ -29,6 +29,7 @@
>  #include <linux/trace.h>
> 
>  static LIST_HEAD(trace_roots);
> +static LIST_HEAD(trace_dirs);
>  static DEFINE_MUTEX(trace_mutex);
> 
>  static int state_open(struct inode *inode, struct file *filp)
> @@ -99,9 +100,19 @@ static void remove_root(struct trace_inf
> 
>  static void remove_tree(struct trace_info *trace)
>  {
> +    struct list_head *pos, *temp;
> +    struct trace_dir *dr = NULL;
> +
>      mutex_lock(&trace_mutex);
>      debugfs_remove(trace->dir);
> 
> +    list_for_each_safe(pos, temp, &trace_dirs) {
> +        dr = list_entry(pos, struct trace_dir, trace_dir_list);
> +        if (dr->ti == trace) {
> +            list_del(pos);
> +             kfree(dr);
> +        }
> +    }
>      if (trace->root) {
>          if (--trace->root->users == 0)
>              remove_root(trace);
> @@ -142,11 +153,17 @@ static struct trace_root *lookup_root(co
>  static struct dentry *create_tree(struct trace_info *trace, const char 
> *root,
>                    const char *name)
>  {
> -    struct dentry *dir = NULL;
> +    struct trace_dir *temp;
> 
>      if (root == NULL || name == NULL)
>          return ERR_PTR(-EINVAL);
> 
> +    temp = kzalloc(sizeof(struct trace_dir), GFP_KERNEL);
> +    if ((temp == NULL) || (strlen(name) > TRACE_NAME_SIZE))
> +        return ERR_PTR(-ENOMEM);
> +
> +    strlcpy(temp->trace_dir_name, name, sizeof(temp->trace_dir_name));
> +
>      mutex_lock(&trace_mutex);
> 
>      trace->root = lookup_root(root);
> @@ -155,17 +172,49 @@ static struct dentry *create_tree(struct
>          goto err;
>      }
> 
> -    dir = debugfs_create_dir(name, trace->root->root);
> -    if (IS_ERR(dir))
> +    temp->trace_root = trace->root->root;
> +    temp->trace_dir = debugfs_create_dir(name, trace->root->root);
> +
> +    if (IS_ERR(temp->trace_dir))
>          remove_root(trace);
> -    else
> +    else {
>          trace->root->users++;
> +        temp->ti = trace;
> +        list_add_tail(&temp->trace_dir_list, &trace_dirs);
> +    }
> 
>  err:
>      mutex_unlock(&trace_mutex);
> -    return dir;
> +    return temp->trace_dir;
>  }
> 
> +int trace_exists(const char *parent_dir, const char *dir,
> +                    struct trace_info **ti)
> +{
> +    struct list_head *pos;
> +    struct trace_root *r;
> +    struct trace_dir *temp;
> +
> +    list_for_each(pos, &trace_roots) {
> +        r = list_entry(pos, struct trace_root, list);
> +        if (!strcmp(parent_dir, r->name))
> +            goto search_dir;
> +    }
> +    return TRACE_PARENT_DIR_ABSENT;
> +
> + search_dir:
> +    list_for_each(pos, &trace_dirs) {
> +        temp = list_entry(pos, struct trace_dir, trace_dir_list);
> +
> +        if (!strcmp(dir, temp->trace_dir_name)) {
> +            *ti = temp->ti;
> +            return TRACE_DIR_EXISTS;
> +        }
> +    }
> +    return TRACE_PARENT_DIR_EXISTS;
> +}
> +EXPORT_SYMBOL_GPL(trace_exists);
> +
>  static int dropped_open(struct inode *inode, struct file *filp)
>  {
>      filp->private_data = inode->i_private;
> @@ -561,3 +610,148 @@ void trace_cleanup(struct trace_info *tr
>      kfree(trace);
>  }
>  EXPORT_SYMBOL_GPL(trace_cleanup);
> +
> +/**
> + *    trace_cleanup_all - Removes all trace directories under a parent_dir
> + *    @parent_dir: Name of the parent directory
> + */
> +void trace_cleanup_all(const char *parent_dir)
> +{
> +    struct list_head *pos, *pos_temp;
> +    struct trace_dir *temp;
> +
> +    list_for_each_safe(pos, pos_temp, &trace_dirs) {
> +        temp = list_entry(pos, struct trace_dir, trace_dir_list);
> +        if (!strncmp(parent_dir, temp->trace_root->d_iname, 
> strlen(parent_dir)))
> +            trace_cleanup(temp->ti);
> +    }
> +}
> +EXPORT_SYMBOL_GPL(trace_cleanup_all);
> +
> +/*
> + * Send formatted trace data to trace channel.
> + */
> +static int trace_printf(struct trace_info *trace, const char *format,
> +                                va_list ap)
> +{
> +    va_list aq;
> +    char *record;
> +    int len, ret = 0;
> +
> +    if (trace_running(trace)) {
> +        va_copy(aq, ap);
> +        len = vsnprintf(NULL, 0, format, aq);
> +        va_end(aq);
> +        record = relay_reserve(trace->rchan, ++len);
> +        if (record)
> +            ret = vsnprintf(record, len, format, ap);
> +    }
> +    return ret;
> +}
> +
> +static inline int init_trace_interface(struct trace_printk_data *tpk)
> +{
> +    int ret = 0;
> +    tpk->exists = trace_exists(tpk->parent_dir, tpk->dir, &tpk->ti);
> +
> +    switch(tpk->exists) {
> +
> +    case TRACE_PARENT_DIR_EXISTS:
> +    case TRACE_PARENT_DIR_ABSENT:
> +        if(!tpk->buf_size)
> +            tpk->buf_size = DEFAULT_TRACE_BUF_SIZE;
> +        if(!tpk->sub_buf_size)
> +            tpk->sub_buf_size = DEFAULT_TRACE_SUB_BUF_NR;
> +        tpk->ti = trace_setup(tpk->parent_dir, tpk->dir,
> +                tpk->buf_size, tpk->sub_buf_size, tpk->flags);
> +        printk(KERN_INFO "Trace interface %s setup\n",
> +                            tpk->ti->dir->d_iname);
> +        if (IS_ERR(tpk->ti)) {
> +            printk(KERN_ERR "Error initialising %s interface\n",
> +                            tpk->ti->dir->d_iname);
> +            return -EPERM;
> +        }
> +    /* Fall through */
> +    case TRACE_DIR_EXISTS:
> +        if (tpk->ti->state == TRACE_SETUP)
> +            ret = trace_start(tpk->ti);
> +        else
> +            ret = -EPERM;
> +    }
> +
> +    return 0;
> +}
> +
> +/**
> + * trace_printk - Output a string to debugfs mount 'directly' using 
> 'trace'
> + * @tpk: Structure containing info such as parent_dir and directory
> + * @format: String containing format string specifiers
> + * @ap: List of arguments
> + */
> +int trace_printk(struct trace_printk_data *tpk, char *format, ...)
> +{
> +    int ret = 0;
> +    va_list(ap);
> +    unsigned long flags = 0;
> +
> +    va_start(ap, format);
> +
> +    ret = init_trace_interface(tpk);
> +    if (unlikely(ret))
> +        return ret;
> +
> +    /* Now do the actual printing */
> +    /* Take an RCU Lock over the trace_info state */
> +    rcu_read_lock();
> +    /* Take a spinlock for the global buffer used by relay */
> +    if (tpk->flags & TRACE_GLOBAL_CHANNEL)
> +        spin_lock_irqsave(&tpk->ti->trace_lock, flags);
> +    ret = trace_printf(tpk->ti, format, ap);
> +    if (tpk->flags & TRACE_GLOBAL_CHANNEL)
> +        spin_unlock_irqrestore(&tpk->ti->trace_lock, flags);
> +    rcu_read_unlock();
> +
> +    va_end(ap);
> +    return ret;
> +}
> +EXPORT_SYMBOL(trace_printk);
> +
> +/**
> + * trace_dump - Output binary into debugfs mount 'directly' using 'trace'
> + * @tpk: Structure containing info such as parent_dir and directory
> + * @output: Data that needs to be output
> + * @output_len: Length of the output data
> + */
> +int trace_dump(struct trace_printk_data *tpk, const void *output,
> +                            const int output_len)
> +{
> +    char *record;
> +    unsigned long flags = 0;
> +    int ret = 0;
> +
> +    ret = init_trace_interface(tpk);
> +    if (unlikely(ret))
> +        return ret;
> +
> +    /* Now do the actual printing */
> +    rcu_read_lock();
> +    /* Take a spinlock for the global buffer used by relay */
> +    if (tpk->flags & TRACE_GLOBAL_CHANNEL)
> +        spin_lock_irqsave(&tpk->ti->trace_lock, flags);
> +    record = relay_reserve(tpk->ti->rchan, output_len);
> +
> +    if (record && trace_running(tpk->ti))
> +        memcpy(record, output, output_len);
> +    else {
> +        if(record)
> +            ret = -EPERM;
> +        else
> +            ret = -ENOMEM;
> +    }
> +    if (tpk->flags & TRACE_GLOBAL_CHANNEL)
> +        spin_unlock_irqrestore(&tpk->ti->trace_lock, flags);
> +    rcu_read_unlock();
> +
> +    return ret;
> +}
> +EXPORT_SYMBOL(trace_dump);
> Index: linux-blktrace-many/samples/trace/fork_new_trace.c
> ===================================================================
> --- /dev/null
> +++ linux-blktrace-many/samples/trace/fork_new_trace.c
> @@ -0,0 +1,99 @@
> +/*
> + * An example of using trace in a kprobes module
> + *
> + * Copyright (C) 2008 IBM Inc.
> + *
> + * K.Prasad <prasad@...ux.vnet.ibm.com>
> + *
> + * 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
> + *
> + * -------
> + * This module creates a trace channel and places a kprobe
> + * on the function do_fork(). The value of current->pid is written to
> + * the trace channel each time the kprobe is hit..
> + *
> + * How to run the example:
> + * $ mount -t debugfs /debug
> + * $ insmod fork_new_trace.ko
> + *
> + * To view the data produced by the module:
> + * $ cat /debug/trace_example/do_fork/trace0
> + *
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/kprobes.h>
> +#include <linux/trace.h>
> +
> +#define SAMPLE_PARENT_DIR "trace_new_example"
> +#define PROBE_POINT "do_fork"
> +
> +static struct kprobe kp;
> +static struct trace_printk_data *tpk;
> +
> +static int handler_pre(struct kprobe *p, struct pt_regs *regs)
> +{
> +    trace_printk(tpk, "%d\n", current->pid);
> +    return 0;
> +}
> +
> +int init_module(void)
> +{
> +    int ret = 0;
> +    int len_parent_dir, len_dir;
> +
> +    /* setup the kprobe */
> +    kp.pre_handler = handler_pre;
> +    kp.post_handler = NULL;
> +    kp.fault_handler = NULL;
> +    kp.symbol_name = PROBE_POINT;
> +    ret = register_kprobe(&kp);
> +    if (ret) {
> +        printk(KERN_ERR "fork_trace: register_kprobe failed\n");
> +        return ret;
> +    }
> +
> +    len_parent_dir = strlen(SAMPLE_PARENT_DIR) + 1;
> +    /* Initialising len_dir to the larger of the two dir names */
> +    len_dir = strlen("kprobe_struct") + 1;
> +
> +    tpk = kzalloc(sizeof(*tpk), GFP_KERNEL);
> +    if(!tpk)
> +        ret = 1;
> +
> +    tpk->parent_dir = SAMPLE_PARENT_DIR;
> +
> +    /* Let's do a binary dump of struct kprobe using trace_dump */
> +    tpk->dir = "kprobes_struct";
> +    tpk->flags = TRACE_GLOBAL_CHANNEL;
> +    trace_dump(tpk, &kp, sizeof(kp));
> +
> +    /* Now change the directory to collect fork pid data */
> +    tpk->dir = PROBE_POINT;
> +
> +    if(ret)
> +        printk(KERN_ERR "Unable to find required free memory. "
> +                "Trace new sample module loading aborted");
> +    return ret;
> +}
> +
> +void cleanup_module(void)
> +{
> +    unregister_kprobe(&kp);
> +
> +    /* Just a single cleanup call passing the parent dir string */
> +    trace_cleanup_all(SAMPLE_PARENT_DIR);
> +}
> +MODULE_LICENSE("GPL");
> Index: linux-blktrace-many/samples/trace/Makefile
> ===================================================================
> --- linux-blktrace-many.orig/samples/trace/Makefile
> +++ linux-blktrace-many/samples/trace/Makefile
> @@ -1,4 +1,4 @@
>  # builds the trace example kernel modules;
>  # then to use (as root):  insmod <fork_trace.ko>
> 
> -obj-$(CONFIG_SAMPLE_TRACE) := fork_trace.o
> +obj-$(CONFIG_SAMPLE_TRACE) := fork_trace.o fork_new_trace.o
> Index: linux-blktrace-many/Documentation/trace.txt
> ===================================================================
> --- linux-blktrace-many.orig/Documentation/trace.txt
> +++ linux-blktrace-many/Documentation/trace.txt
> @@ -150,6 +150,28 @@ The steps a kernel data provider takes t
>  5) Destroy the trace channel and underlying relay channel -
>     trace_cleanup().
> 
> +Alternatively the user may choose to make use of two new interfaces --
> +trace_printk() and trace_dump() -- to setup trace interface and
> +trace_cleanup_all() to tear-down the same.
> +
> +Steps to use:
> +1) Create and populate an instance of trace_printk_data structure. The 
> fields
> +   parent_dir and dir are mandatory. The fields buf_size, sub_buf_size 
> and flags
> +   are optional and will take default values if not populated. The field
> +   'exists' and ti are for the trace infrastructure to use. The pointer 
> to the
> +   'struct trace_info' i.e. ti may be used to perform fine granular 
> operations
> +   such as determine the state of the 'trace', stop individual traces, 
> etc.
> +2) Default values for buf_size and sub_buf_size are 4096, 40 respectively.
> +3) Use trace_dump() to output binary data which may be acted upon by a
> +   high-level program (say dumping a structure). trace_printk() can be 
> used
> +   for string output. Pass a pointer to the instance of trace_printk_data
> +   structure to these functions along with other parameters. The output 
> from
> +   these functions can be found at
> +   <debugfs_mount>/<parent_dir>/<dir>/trace<0..n>.
> +4) trace_cleanup_all() for a given parent directory will cleanup and 
> remove all
> +   trace directories created under the specified directory.
> +5) Sample code for the same can be found in samples/trace/fork_new_trace.c
> +
>  Kernel Configuration
>  --------------------
>  To use trace, configure your kernel with CONFIG_TRACE=y. Trace depends on
> 

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