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Subject[RFC PATCH 2/4] tracing: Turn "id"->i_private into call->event.type
ftrace_event_id_fops and event_id_read() is overcomplicated.

1. Change event_create_dir() to pass "data = call->event.type"
to debugfs_create_file().

This means that ftrace_event_id_fops doesn't need .open()
and event_id_read() can simply print (int)i_private

2. event_id_read() has no reason to kmalloc "struct trace_seq"
(more than PAGE_SIZE!), it can use a small buffer.

Note: "if (*ppos) return 0" looks strange and unneeded,
simple_read_from_buffer(ppos) should handle this case corrrectly.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
kernel/trace/trace_events.c | 26 +++++++++-----------------
1 files changed, 9 insertions(+), 17 deletions(-)

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index cbd1a57..cefbe85 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -962,24 +962,17 @@ static int trace_format_open(struct inode *inode, struct file *file)
static ssize_t
event_id_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
{
- struct ftrace_event_call *call = filp->private_data;
- struct trace_seq *s;
- int r;
+ int id = (long)ACCESS_ONCE(file_inode(filp)->i_private);
+ char buf[32];
+ int len;

+ if (!id)
+ return -ENODEV;
if (*ppos)
return 0;

- s = kmalloc(sizeof(*s), GFP_KERNEL);
- if (!s)
- return -ENOMEM;
-
- trace_seq_init(s);
- trace_seq_printf(s, "%d\n", call->event.type);
-
- r = simple_read_from_buffer(ubuf, cnt, ppos,
- s->buffer, s->len);
- kfree(s);
- return r;
+ len = sprintf(buf, "%d\n", id);
+ return simple_read_from_buffer(ubuf, cnt, ppos, buf, len);
}

static ssize_t
@@ -1264,7 +1257,6 @@ static const struct file_operations ftrace_event_format_fops = {
};

static const struct file_operations ftrace_event_id_fops = {
- .open = tracing_open_generic,
.read = event_id_read,
.llseek = default_llseek,
};
@@ -1496,8 +1488,8 @@ event_create_dir(struct dentry *parent,

#ifdef CONFIG_PERF_EVENTS
if (call->event.type && call->class->reg)
- trace_create_file("id", 0444, file->dir, call,
- id);
+ trace_create_file("id", 0444, file->dir,
+ (void*)(long)call->event.type, id);
#endif

/*
--
1.5.5.1


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