Re: [PATCH 2/5] tracing_bprintk: don't increment @pos in t_start()

From: Wang Liming
Date: Sun Jun 21 2009 - 22:32:25 EST


Li Zefan wrote:
Wang Liming wrote:
Hi,

Li Zefan wrote:
It's wrong to increment @pos in t_start(), otherwise we'll lose
some entries when reading printk_formats, if the output is large
than PAGE_SIZE.

[ Impact: fix missing entries when reading printk_formats ]

Reported-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
Signed-off-by: Li Zefan <lizf@xxxxxxxxxxxxxx>
---
kernel/trace/trace_printk.c | 26 ++++++--------------------
1 files changed, 6 insertions(+), 20 deletions(-)

diff --git a/kernel/trace/trace_printk.c b/kernel/trace/trace_printk.c
index 9bece96..7b62781 100644
--- a/kernel/trace/trace_printk.c
+++ b/kernel/trace/trace_printk.c
@@ -155,25 +155,19 @@ int __ftrace_vprintk(unsigned long ip, const
char *fmt, va_list ap)
EXPORT_SYMBOL_GPL(__ftrace_vprintk);
static void *
-t_next(struct seq_file *m, void *v, loff_t *pos)
+t_start(struct seq_file *m, loff_t *pos)
{
- const char **fmt = m->private;
- const char **next = fmt;
-
- (*pos)++;
+ const char **fmt = __start___trace_bprintk_fmt + *pos;
if ((unsigned long)fmt >= (unsigned long)__stop___trace_bprintk_fmt)
return NULL;
-
- next = fmt;
- m->private = ++next;
-
return fmt;
}
-static void *t_start(struct seq_file *m, loff_t *pos)
+static void *t_next(struct seq_file *m, void * v, loff_t *pos)
{
- return t_next(m, NULL, pos);
+ (*pos)++;
+ return t_start(m, pos);
}
I prefer to .start to call .next, so I rewrite it to following:


Thanks for the comment, but I don't think .next calls .start is bad,
and I'm not the only one doing this. Grep c_start() to see some of
them.
Yes, you are not the only one, but it's the only one in the tracing code. :)
I just think we should make the seq_* uniform so that we can understand them more clearly.

Liming Wang



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