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 <wrapper/vmalloc.h>
  20 #include <lttng/events.h>
  21
  22 #define TP_MODULE_NOAUTOLOAD
  23 #define LTTNG_PACKAGE_BUILD
  24 #define CREATE_TRACE_POINTS
  25 #define TRACE_INCLUDE_PATH instrumentation/events
  26 #define TRACE_INCLUDE_FILE lttng
  27 #define LTTNG_INSTRUMENTATION
  28
  29 #include <instrumentation/events/lttng.h>
  30
  31 /* Events written through logger are truncated at 1024 bytes */
  32 #define LTTNG_LOGGER_COUNT_MAX  1024
  33 #define LTTNG_LOGGER_FILE       "lttng-logger"
  34
  35 DEFINE_TRACE(lttng_logger);
  36
  37 static struct proc_dir_entry *lttng_logger_dentry;
  38
  39 /**
  40  * lttng_logger_write - write a userspace string into the trace system
  41  * @file: file pointer
  42  * @user_buf: user string
  43  * @count: length to copy
  44  * @ppos: file position
  45  *
  46  * Copy a userspace string into a trace event named "lttng:logger".
  47  * Copies at most @count bytes into the event "msg" dynamic array.
  48  * Truncates the count at LTTNG_LOGGER_COUNT_MAX. Returns the number of
  49  * bytes copied from the source.
  50  * Return -1 on error, with EFAULT errno.
  51  */
  52 static
  53 ssize_t lttng_logger_write(struct file *file, const char __user *user_buf,
  54                     size_t count, loff_t *ppos)
  55 {
  56         int nr_pages = 1, i;
  57         unsigned long uaddr = (unsigned long) user_buf;
  58         struct page *pages[2];
  59         ssize_t written;
  60         int ret;
  61
  62         /* Truncate count */
  63         if (unlikely(count > LTTNG_LOGGER_COUNT_MAX))
  64                 count = LTTNG_LOGGER_COUNT_MAX;
  65
  66         /* How many pages are we dealing with ? */
  67         if (unlikely((uaddr & PAGE_MASK) != ((uaddr + count) & PAGE_MASK)))
  68                 nr_pages = 2;
  69
  70         /* Pin userspace pages */
  71         ret = get_user_pages_fast(uaddr, nr_pages, 0, pages);
  72         if (unlikely(ret < nr_pages)) {
  73                 if (ret > 0) {
  74                         BUG_ON(ret != 1);
  75                         put_page(pages[0]);
  76                 }
  77                 written = -EFAULT;
  78                 goto end;
  79         }
  80
  81         /* Trace the event */
  82         trace_lttng_logger(user_buf, count);
  83         written = count;
  84         *ppos += written;
  85
  86         for (i = 0; i < nr_pages; i++)
  87                 put_page(pages[i]);
  88 end:
  89         return written;
  90 }
  91
  92 static const struct file_operations lttng_logger_operations = {
  93         .write = lttng_logger_write,
  94 };
  95
  96 /*
  97  * Linux 5.6 introduced a separate proc_ops struct for /proc operations
  98  * to decouple it from the vfs.
  99  */
 100 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(5,6,0))
 101 static const struct proc_ops lttng_logger_proc_ops = {
 102         .proc_write = lttng_logger_write,
 103 };
 104 #else
 105 #define lttng_logger_proc_ops lttng_logger_operations
 106 #endif
 107
 108 static struct miscdevice logger_dev = {
 109         .minor = MISC_DYNAMIC_MINOR,
 110         .name = "lttng-logger",
 111         .mode = 0666,
 112         .fops = &lttng_logger_operations
 113 };
 114
 115 int __init lttng_logger_init(void)
 116 {
 117         int ret = 0;
 118
 119         wrapper_vmalloc_sync_mappings();
 120
 121         /* /dev/lttng-logger */
 122         ret = misc_register(&logger_dev);
 123         if (ret) {
 124                 printk(KERN_ERR "Error creating LTTng logger device\n");
 125                 goto error;
 126         }
 127
 128         /* /proc/lttng-logger */
 129         lttng_logger_dentry = proc_create_data(LTTNG_LOGGER_FILE,
 130                                 S_IRUGO | S_IWUGO, NULL,
 131                                 &lttng_logger_proc_ops, NULL);
 132         if (!lttng_logger_dentry) {
 133                 printk(KERN_ERR "Error creating LTTng logger proc file\n");
 134                 ret = -ENOMEM;
 135                 goto error_proc;
 136         }
 137
 138         /* Init */
 139         ret = __lttng_events_init__lttng();
 140         if (ret)
 141                 goto error_events;
 142         return ret;
 143
 144 error_events:
 145         remove_proc_entry("lttng-logger", NULL);
 146 error_proc:
 147         misc_deregister(&logger_dev);
 148 error:
 149         return ret;
 150 }
 151
 152 void lttng_logger_exit(void)
 153 {
 154         __lttng_events_exit__lttng();
 155         if (lttng_logger_dentry)
 156                 remove_proc_entry("lttng-logger", NULL);
 157         misc_deregister(&logger_dev);
 158 }