[PATCH -mm 2/5] fault-inject: parse as natural 1-based value for fail-nth write interface

[Akinobu Mita <akinobu.mita@gmail.com>]

The value written to fail-nth file is parsed as 0-based.  Parsing as
one-based is more natural to understand and it enables to cancel the
previous setup by simply writing '0'.

This change also convert task->fail_nth from signed to unsigned int.

Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
---
 Documentation/fault-injection/fault-injection.txt | 7 +++----
 fs/proc/base.c                                    | 9 ++++-----
 include/linux/sched.h                             | 2 +-
 3 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/Documentation/fault-injection/fault-injection.txt b/Documentation/fault-injection/fault-injection.txt
index 192d8cb..a321905 100644
--- a/Documentation/fault-injection/fault-injection.txt
+++ b/Documentation/fault-injection/fault-injection.txt
@@ -138,8 +138,8 @@ o proc entries
 
 - /proc/self/task/<current-tid>/fail-nth:
 
-	Write to this file of integer N makes N-th call in the current task fail
-	(N is 0-based). Read from this file returns a single char 'Y' or 'N'
+	Write to this file of integer N makes N-th call in the task fail.
+	Read from this file returns a single char 'Y' or 'N'
 	that says if the fault setup with a previous write to this file was
 	injected or not, and disables the fault if it wasn't yet injected.
 	Note that this file enables all types of faults (slab, futex, etc).
@@ -320,7 +320,7 @@ int main()
 	system("echo N > /sys/kernel/debug/failslab/ignore-gfp-wait");
 	sprintf(buf, "/proc/self/task/%ld/fail-nth", syscall(SYS_gettid));
 	fail_nth = open(buf, O_RDWR);
-	for (i = 0;; i++) {
+	for (i = 1;; i++) {
 		sprintf(buf, "%d", i);
 		write(fail_nth, buf, strlen(buf));
 		res = socketpair(AF_LOCAL, SOCK_STREAM, 0, fds);
@@ -339,7 +339,6 @@ int main()
 
 An example output:
 
-0-th fault Y: res=-1/23
 1-th fault Y: res=-1/23
 2-th fault Y: res=-1/23
 3-th fault Y: res=-1/12
diff --git a/fs/proc/base.c b/fs/proc/base.c
index c85376b..42c52e2 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1363,7 +1363,8 @@ static ssize_t proc_fail_nth_write(struct file *file, const char __user *buf,
 				   size_t count, loff_t *ppos)
 {
 	struct task_struct *task;
-	int err, n;
+	int err;
+	unsigned int n;
 
 	task = get_proc_task(file_inode(file));
 	if (!task)
@@ -1371,12 +1372,10 @@ static ssize_t proc_fail_nth_write(struct file *file, const char __user *buf,
 	put_task_struct(task);
 	if (task != current)
 		return -EPERM;
-	err = kstrtoint_from_user(buf, count, 0, &n);
+	err = kstrtouint_from_user(buf, count, 0, &n);
 	if (err)
 		return err;
-	if (n < 0 || n == INT_MAX)
-		return -EINVAL;
-	current->fail_nth = n + 1;
+	current->fail_nth = n;
 	return count;
 }
 
diff --git a/include/linux/sched.h b/include/linux/sched.h
index f0f0854..bec5d97 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -945,7 +945,7 @@ struct task_struct {
 
 #ifdef CONFIG_FAULT_INJECTION
 	int				make_it_fail;
-	int fail_nth;
+	unsigned int			fail_nth;
 #endif
 	/*
 	 * When (nr_dirtied >= nr_dirtied_pause), it's time to call
-- 
2.7.4