probes/lttng.c

   1 /* SPDX-License-Identifier: (GPL-2.0-only or LGPL-2.1-only)
   2  *
   3  * lttng.c
   4  *
   5  * LTTng logger ABI
   6  *
   7  * Copyright (C) 2008-2014 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   8  */
   9
  10 #include <linux/module.h>
  11 #include <linux/tracepoint.h>
  12 #include <linux/uaccess.h>
  13 #include <linux/gfp.h>
  14 #include <linux/fs.h>
  15 #include <linux/proc_fs.h>
  16 #include <linux/slab.h>
  17 #include <linux/mm.h>
  18 #include <linux/miscdevice.h>
  19 #include <lttng-events.h>
  20
  21 #define TP_MODULE_NOAUTOLOAD
  22 #define LTTNG_PACKAGE_BUILD
  23 #define CREATE_TRACE_POINTS
  24 #define TRACE_INCLUDE_PATH instrumentation/events/lttng-module
  25 #define TRACE_INCLUDE_FILE lttng
  26 #define LTTNG_INSTRUMENTATION
  27
  28 #include <instrumentation/events/lttng-module/lttng.h>
  29
  30 /* Events written through logger are truncated at 1024 bytes */
  31 #define LTTNG_LOGGER_COUNT_MAX  1024
  32 #define LTTNG_LOGGER_FILE       "lttng-logger"
  33
  34 DEFINE_TRACE(lttng_logger);
  35
  36 static struct proc_dir_entry *lttng_logger_dentry;
  37
  38 /**
  39  * lttng_logger_write - write a userspace string into the trace system
  40  * @file: file pointer
  41  * @user_buf: user string
  42  * @count: length to copy
  43  * @ppos: file position
  44  *
  45  * Copy a userspace string into a trace event named "lttng:logger".
  46  * Copies at most @count bytes into the event "msg" dynamic array.
  47  * Truncates the count at LTTNG_LOGGER_COUNT_MAX. Returns the number of
  48  * bytes copied from the source.
  49  * Return -1 on error, with EFAULT errno.
  50  */
  51 static
  52 ssize_t lttng_logger_write(struct file *file, const char __user *user_buf,
  53                     size_t count, loff_t *ppos)
  54 {
  55         int nr_pages = 1, i;
  56         unsigned long uaddr = (unsigned long) user_buf;
  57         struct page *pages[2];
  58         ssize_t written;
  59         int ret;
  60
  61         /* Truncate count */
  62         if (unlikely(count > LTTNG_LOGGER_COUNT_MAX))
  63                 count = LTTNG_LOGGER_COUNT_MAX;
  64
  65         /* How many pages are we dealing with ? */
  66         if (unlikely((uaddr & PAGE_MASK) != ((uaddr + count) & PAGE_MASK)))
  67                 nr_pages = 2;
  68
  69         /* Pin userspace pages */
  70         ret = get_user_pages_fast(uaddr, nr_pages, 0, pages);
  71         if (unlikely(ret < nr_pages)) {
  72                 if (ret > 0) {
  73                         BUG_ON(ret != 1);
  74                         put_page(pages[0]);
  75                 }
  76                 written = -EFAULT;
  77                 goto end;
  78         }
  79
  80         /* Trace the event */
  81         trace_lttng_logger(user_buf, count);
  82         written = count;
  83         *ppos += written;
  84
  85         for (i = 0; i < nr_pages; i++)
  86                 put_page(pages[i]);
  87 end:
  88         return written;
  89 }
  90
  91 static const struct file_operations lttng_logger_operations = {
  92         .write = lttng_logger_write,
  93 };
  94
  95 /*
  96  * Linux 5.6 introduced a separate proc_ops struct for /proc operations
  97  * to decouple it from the vfs.
  98  */
  99 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(5,6,0))
 100 static const struct proc_ops lttng_logger_proc_ops = {
 101         .proc_write = lttng_logger_write,
 102 };
 103 #else
 104 #define lttng_logger_proc_ops lttng_logger_operations
 105 #endif
 106
 107 static struct miscdevice logger_dev = {
 108         .minor = MISC_DYNAMIC_MINOR,
 109         .name = "lttng-logger",
 110         .mode = 0666,
 111         .fops = &lttng_logger_operations
 112 };
 113
 114 int __init lttng_logger_init(void)
 115 {
 116         int ret = 0;
 117
 118         /* /dev/lttng-logger */
 119         ret = misc_register(&logger_dev);
 120         if (ret) {
 121                 printk(KERN_ERR "Error creating LTTng logger device\n");
 122                 goto error;
 123         }
 124
 125         /* /proc/lttng-logger */
 126         lttng_logger_dentry = proc_create_data(LTTNG_LOGGER_FILE,
 127                                 S_IRUGO | S_IWUGO, NULL,
 128                                 &lttng_logger_proc_ops, NULL);
 129         if (!lttng_logger_dentry) {
 130                 printk(KERN_ERR "Error creating LTTng logger proc file\n");
 131                 ret = -ENOMEM;
 132                 goto error_proc;
 133         }
 134
 135         /* Init */
 136         ret = __lttng_events_init__lttng();
 137         if (ret)
 138                 goto error_events;
 139         return ret;
 140
 141 error_events:
 142         remove_proc_entry("lttng-logger", NULL);
 143 error_proc:
 144         misc_deregister(&logger_dev);
 145 error:
 146         return ret;
 147 }
 148
 149 void lttng_logger_exit(void)
 150 {
 151         __lttng_events_exit__lttng();
 152         if (lttng_logger_dentry)
 153                 remove_proc_entry("lttng-logger", NULL);
 154         misc_deregister(&logger_dev);
 155 }