fault-inject: make fail-nth read/write interface symmetric

The read interface for fail-nth looks a bit odd. Read from this file returns "NYYYY..." or "YYYYY..." (this makes me surprise when cat this file). Because there is no EOF condition. The first character indicates current->fail_nth is zero or not, and then current->fail_nth is reset to zero. Just returning task->fail_nth value is more natural to understand. Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Akinobu Mita <[email protected]> Cc: Dmitry Vyukov <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
chewitt · Jul 14, 2017 · bfc7409 · bfc7409
1 parent 9049f2f
commit bfc7409
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Showing 2 changed files with 13 additions and 14 deletions.
diff --git a/Documentation/fault-injection/fault-injection.txt b/Documentation/fault-injection/fault-injection.txt
@@ -139,9 +139,9 @@ o proc entries
 - /proc/self/task/<current-tid>/fail-nth:
 
 	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.
+	Read from this file returns a integer value. A value of '0' indicates
+	that the fault setup with a previous write to this file was injected.
+	A positive integer N indicates that the fault wasn't yet injected.
 	Note that this file enables all types of faults (slab, futex, etc).
 	This setting takes precedence over all other generic debugfs settings
 	like probability, interval, times, etc. But per-capability settings
@@ -325,13 +325,14 @@ int main()
 		write(fail_nth, buf, strlen(buf));
 		res = socketpair(AF_LOCAL, SOCK_STREAM, 0, fds);
 		err = errno;
-		read(fail_nth, buf, 1);
+		pread(fail_nth, buf, sizeof(buf), 0);
 		if (res == 0) {
 			close(fds[0]);
 			close(fds[1]);
 		}
-		printf("%d-th fault %c: res=%d/%d\n", i, buf[0], res, err);
-		if (buf[0] != 'Y')
+		printf("%d-th fault %c: res=%d/%d\n", i, atoi(buf) ? 'N' : 'Y',
+			res, err);
+		if (atoi(buf))
 			break;
 	}
 	return 0;

diff --git a/fs/proc/base.c b/fs/proc/base.c
@@ -1380,21 +1380,19 @@ static ssize_t proc_fail_nth_read(struct file *file, char __user *buf,
 				  size_t count, loff_t *ppos)
 {
 	struct task_struct *task;
-	int err;
+	char numbuf[PROC_NUMBUF];
+	ssize_t len;
 
 	task = get_proc_task(file_inode(file));
 	if (!task)
 		return -ESRCH;
 	put_task_struct(task);
 	if (task != current)
 		return -EPERM;
-	if (count < 1)
-		return -EINVAL;
-	err = put_user((char)(current->fail_nth ? 'N' : 'Y'), buf);
-	if (err)
-		return err;
-	current->fail_nth = 0;
-	return 1;
+	len = snprintf(numbuf, sizeof(numbuf), "%u\n", task->fail_nth);
+	len = simple_read_from_buffer(buf, count, ppos, numbuf, len);
+
+	return len;
 }
 
 static const struct file_operations proc_fail_nth_operations = {