[PATCH] fs: fix bug about seq_read read nothing

From: biannm
Date: Wed Jun 25 2008 - 05:48:37 EST


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@xxxxxxxxxxxxxx>

---
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

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