[PATCH] /proc/sysrq-trigger: trigger sysrq functions via

This makes sysrq facilities available to remote users.

Writing a 'C' to /proc/sysrq-trigger receives the same treatment as typing
sysrq-C on the local keyboard.

Documentation/sysrq.txt

@@ -36,6 +36,10 @@ On PowerPC - Press 'ALT - Print Screen (or F13) - <command key>,
 On other - If you know of the key combos for other architectures, please
            let me know so I can add them to this section.
 
+On all -  write a character to /proc/sysrq-trigger.  eg:
+
+		echo t > /proc/sysrq-trigger
+
 *  What are the 'command' keys?
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 'r'     - Turns off keyboard raw mode and sets it to XLATE.

fs/proc/proc_misc.c

@@ -42,6 +42,7 @@
 #include <linux/blkdev.h>
 #include <linux/hugetlb.h>
 #include <linux/jiffies.h>
+#include <linux/sysrq.h>
 #include <asm/uaccess.h>
 #include <asm/pgtable.h>
 #include <asm/io.h>
@@ -521,6 +522,28 @@ static struct file_operations proc_profile_operations = {
 	.write		= write_profile,
 };
 
+#ifdef CONFIG_MAGIC_SYSRQ
+/*
+ * writing 'C' to /proc/sysrq-trigger is like sysrq-C
+ */
+static ssize_t write_sysrq_trigger(struct file *file, const char *buf,
+				     size_t count, loff_t *ppos)
+{
+	if (count) {
+		char c;
+
+		if (get_user(c, buf))
+			return -EFAULT;
+		handle_sysrq(c, NULL, NULL);
+	}
+	return count;
+}
+
+static struct file_operations proc_sysrq_trigger_operations = {
+	.write		= write_sysrq_trigger,
+};
+#endif
+
 struct proc_dir_entry *proc_root_kcore;
 
 static void create_seq_entry(char *name, mode_t mode, struct file_operations *f)
@@ -592,6 +615,11 @@ void __init proc_misc_init(void)
 			entry->size = (1+prof_len) * sizeof(unsigned int);
 		}
 	}
+#ifdef CONFIG_MAGIC_SYSRQ
+	entry = create_proc_entry("sysrq-trigger", S_IWUSR, NULL);
+	if (entry)
+		entry->proc_fops = &proc_sysrq_trigger_operations;
+#endif
 #ifdef CONFIG_PPC32
 	{
 		extern struct file_operations ppc_htab_operations;