Re: [PATCH 2/8] ksym_tracer: Rewrite ksym_trace_filter_read()

K.Prasad
2009-07-11T05:54:39Z

On Tue, Jul 07, 2009 at 01:52:52PM +0800, Li Zefan wrote:
> Reading ksym_trace_filter gave me some arbitrary characters,
> when it should show nothing. It's because buf is not initialized
> when there's no filter.
>

I started noticing this behaviour recently.

A simple
char buf[KSYM_FILTER_ENTRY_LEN * KSYM_TRACER_MAX] = "\0";
solves the problem.

> Also reduce stack usage by about 512 bytes.
>

The stack usage would be much lesser on other architectures with fewer
breakpoint registers (like PPC64), and should really be an issue.

> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
> ---
> kernel/trace/trace_ksym.c | 29 ++++++++++++++++++-----------
> 1 files changed, 18 insertions(+), 11 deletions(-)
>
> diff --git a/kernel/trace/trace_ksym.c b/kernel/trace/trace_ksym.c
> index 085ff05..b6710d3 100644
> --- a/kernel/trace/trace_ksym.c
> +++ b/kernel/trace/trace_ksym.c
> @@ -35,7 +35,6 @@
> #define KSYM_TRACER_MAX HBP_NUM
>
> #define KSYM_TRACER_OP_LEN 3 /* rw- */
> -#define KSYM_FILTER_ENTRY_LEN (KSYM_NAME_LEN + KSYM_TRACER_OP_LEN + 1)
>
> struct trace_ksym {
> struct hw_breakpoint *ksym_hbp;
> @@ -230,25 +229,33 @@ static ssize_t ksym_trace_filter_read(struct file *filp, char __user *ubuf,
> {
> struct trace_ksym *entry;
> struct hlist_node *node;
> - char buf[KSYM_FILTER_ENTRY_LEN * KSYM_TRACER_MAX];
> - ssize_t ret, cnt = 0;
> + struct trace_seq *s;
> + ssize_t cnt = 0;
> + int ret;
> +
> + s = kmalloc(sizeof(*s), GFP_KERNEL);
> + if (!s)
> + return -ENOMEM;
> + trace_seq_init(s);
>
> mutex_lock(&ksym_tracer_mutex);
>
> hlist_for_each_entry(entry, node, &ksym_filter_head, ksym_hlist) {
> - cnt += snprintf(&buf[cnt], KSYM_FILTER_ENTRY_LEN - cnt, "%s:",
> - entry->ksym_hbp->info.name);
> + ret = trace_seq_printf(s, "%s:", entry->ksym_hbp->info.name);
> if (entry->ksym_hbp->info.type == HW_BREAKPOINT_WRITE)
> - cnt += snprintf(&buf[cnt], KSYM_FILTER_ENTRY_LEN - cnt,
> - "-w-\n");
> + ret = trace_seq_puts(s, "-w-\n");
> else if (entry->ksym_hbp->info.type == HW_BREAKPOINT_RW)
> - cnt += snprintf(&buf[cnt], KSYM_FILTER_ENTRY_LEN - cnt,
> - "rw-\n");
> + ret = trace_seq_puts(s, "rw-\n");
> + WARN_ON_ONCE(!ret);

Given that this change uses the tracer defined functions and a seq-file
implementation, the patch is welcome.

Thanks,
K.Prasad