[PATCH] deal with the first call of ->show() generating no output

seq_read() has a subtle bug - we want the first loop there to go
until at least one *non-empty* record had fit entirely into buffer.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 9 insertions, 2 deletions

diff --git a/fs/seq_file.c b/fs/seq_file.c
index 5d54205e486b..bd20f7f5a933 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -108,9 +108,9 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
                         goto Done;
         }
         /* we need at least one record in buffer */
+        pos = m->index;
+        p = m->op->start(m, &pos);
         while (1) {
-                pos = m->index;
-                p = m->op->start(m, &pos);
                 err = PTR_ERR(p);
                 if (!p || IS_ERR(p))
                         break;
@@ -119,6 +119,11 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
                         break;
                 if (unlikely(err))
                         m->count = 0;
+                if (unlikely(!m->count)) {
+                        p = m->op->next(m, p, &pos);
+                        m->index = pos;
+                        continue;
+                }
                 if (m->count < m->size)
                         goto Fill;
                 m->op->stop(m, p);
@@ -128,6 +133,8 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
                         goto Enomem;
                 m->count = 0;
                 m->version = 0;
+                pos = m->index;
+                p = m->op->start(m, &pos);
         }
         m->op->stop(m, p);
         m->count = 0;