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/1491490561-10485-4-git-send-email-akinobu.mita@gmail.com
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/Documentation/fault-injection/fault-injection.txt b/Documentation/fault-injection/fault-injection.txt
index a32190508751c330422b3d7aa40419fb84276fde..370ddcbc2b44173d9ddbafc48635b9ab4fa41df7 100644 (file)
--- 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
index c1fdaecb8d23c99009d2aec5ec635f86b99ebd5b..7d795d28dd02954234bab6d8eda1cadb20c771fd 100644 (file)
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1380,7 +1380,8 @@ 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)
@@ -1388,13 +1389,10 @@ static ssize_t proc_fail_nth_read(struct file *file, char __user *buf,
        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 = {