[PATCH] fs: fix bug about seq_read read nothing

[biannm <biannm@cn.fujitsu.com>]

When i used seq_file to read a proc file, i got a bug of seq_read.
If show() skip the first element or the size of first element is 0, 
and the size of second element is larger than the seq_file->size at 
the same time, seq_read will return 0, so nothing can be read from
the proc file.

So, if seq_read will return because it finds the element is biger 
than the m->buf, it must make sure either some date was filled to 
m->buf by show(), or some data was flushed to the user buf before, 
if not,it should increase the m->buf until it can read this element.


Signed-off-by: Bian Naimeng  <biannm@cn.fujitsu.com>

---
 fs/seq_file.c |   12 +++++++++++-
 1 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/fs/seq_file.c b/fs/seq_file.c
index 3f54dbd..ab1ed27 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -107,6 +107,7 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
 		if (!size)
 			goto Done;
 	}
+First_record:
 	/* we need at least one record in buffer */
 	while (1) {
 		pos = m->index;
@@ -145,8 +146,17 @@ Fill:
 		err = m->op->show(m, p);
 		if (m->count == m->size || err) {
 			m->count = offs;
-			if (likely(err <= 0))
+			if (err < 0)
 				break;
+			/* If no data flush to the user buf and nothing was read
+			 * by show() before,it should increase the m->buf until
+			 * it can read this element.
+			*/
+			if (err == 0 && m->count == 0 && copied == 0) {
+				m->index = next;
+				m->op->stop(m, p);
+				goto First_record;
+			}
 		}
 		pos = next;
 	}
-- 
1.5.4.rc3