[PATCH] deal with the first call of ->show() generating no output
Al Viro [Sun, 24 Aug 2008 11:45:33 +0000 (07:45 -0400)]
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>

fs/seq_file.c

index 5d54205..bd20f7f 100644 (file)
@@ -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;