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Subject[PATCH] 2.4.6: /proc/null - counter for /dev/null traffic
Hello Linus,

Below is patch (for 2.4.6, 2.4.5)
to add support /proc/null - a counter for /dev/null's write traffic

Why not ? Some time it shows very ineteresting things.
For example - Mozilla write 22Mb to /dev/null just at start.

Was tested for two weeks on Intel-platfom with help of my friends.

--- drivers/char/mem.c.orig Thu Jul 5 14:22:28 2001
+++ drivers/char/mem.c Thu Jul 5 14:22:39 2001
@@ -3,6 +3,21 @@
*
* Copyright (C) 1991, 1992 Linus Torvalds
*
+ * Added /proc/null support.
+ * Jun-25-2001, Pavel Yakovlev <hac@subscribe.ru>
+ *
+ * About:
+ *
+ * /proc/null - counter for /dev/null's write traffic
+ * A counter is 4 * unsigned long width (4 is default, configured by WRITE_NULL_LEN)
+ *
+ * Usage:
+ *
+ * echo 0 >/proc/null - reset to 0
+ *
+ * bc </proc/null - bytes writed to /dev/null
+ *
+ *
* Added devfs support.
* Jan-11-1998, C. Scott Ananian <cananian@alumni.princeton.edu>
* Shared /dev/zero mmaping support, Feb 2000, Kanoj Sarcar <kanoj@sgi.com>
@@ -21,6 +36,7 @@
#include <linux/raw.h>
#include <linux/tty.h>
#include <linux/capability.h>
+#include <linux/proc_fs.h>

#include <asm/uaccess.h>
#include <asm/io.h>
@@ -336,9 +352,65 @@
return 0;
}

+
+
+typedef unsigned long wnc_t;
+
+#define WRITE_NULL_LEN 4
+static wnc_t write_null_count[WRITE_NULL_LEN];
+
static ssize_t write_null(struct file * file, const char * buf,
size_t count, loff_t *ppos)
{
+ wnc_t old_val;
+ int i;
+
+ old_val = write_null_count[0];
+ if ((write_null_count[0] += count) < old_val) {
+ for ( i = 1; i < WRITE_NULL_LEN; i++) {
+ old_val = write_null_count[i];
+ if (++write_null_count[i] > old_val)
+ break;
+
+ }
+ if (i == WRITE_NULL_LEN)
+ printk("/dev/null overflow ;)\n");
+ }
+
+ return count;
+}
+
+static int null_proc_read(char *buf, char **start, off_t offset,
+ int count, int *eof, void *data)
+{
+ int len = 0;
+ int i;
+
+ for ( i = 0; i < WRITE_NULL_LEN; i++) {
+ len += sprintf(buf+len,"%lu *2^%i+\\\n",write_null_count[i],i*sizeof(wnc_t)*8);
+ }
+ len += sprintf(buf+len,"0\n");
+
+ /* from fs/proc/proc_misc.c::proc_calc_metric() */
+
+ if (len <= offset+count) *eof = 1;
+ *start = buf + offset;
+ len -= offset;
+ if (len>count) len = count;
+ if (len<0) len = 0;
+ return len;
+
+ /* end from ... */
+}
+
+static int null_proc_write(struct file *file, const char *buf,
+ unsigned long count, void *data)
+{
+ int i;
+ for ( i = 0; i < WRITE_NULL_LEN; i++) {
+ write_null_count[i] = 0;
+ }
+
return count;
}

@@ -434,6 +506,12 @@
return written ? written : -EFAULT;
}

+static ssize_t write_zero(struct file * file, const char * buf,
+ size_t count, loff_t *ppos)
+{
+ return count;
+}
+
static int mmap_zero(struct file * file, struct vm_area_struct * vma)
{
if (vma->vm_flags & VM_SHARED)
@@ -490,7 +568,6 @@
#define mmap_kmem mmap_mem
#define zero_lseek null_lseek
#define full_lseek null_lseek
-#define write_zero write_null
#define read_full read_zero
#define open_mem open_port
#define open_kmem open_mem
@@ -609,6 +686,13 @@

int __init chr_dev_init(void)
{
+ struct proc_dir_entry *ent = create_proc_entry("null", S_IRUGO | S_IWUSR | S_IWGRP, NULL);
+ if (ent) {
+ ent->read_proc = &null_proc_read;
+ ent->write_proc = &null_proc_write;
+ } else
+ printk("unable to create /proc/null read entry\n");
+
if (devfs_register_chrdev(MEM_MAJOR,"mem",&memory_fops))
printk("unable to get major %d for memory devs\n", MEM_MAJOR);
memory_devfs_register();
--------------------------------------
Павел Яковлев
mailto: hac@subscribe.ru ICQ 8085803 PPY-RIPN
технический директор
ЗАО "Интернет-Проекты"
--------------------------------------
"God is real, unless declared integer"

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