On Wed, 22 Jul 2020 16:49:52 +0200
Vincent Whitchurch <vincent.whitchu...@axis.com> wrote:
> Do we really need a separate tracing event for this? Why not just:
> >
> > ftrace_vprintk(fmt + strlen(KERN_DEBUG), args);
>
> Thanks, I tried that out now and it seems to work, but it results in the
> trace_printk() splat (even if the feature is not used), though:
>
> **********************************************************
> ** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **
> ** **
> ** trace_printk() being used. Allocating extra memory. **
> ** **
> ** This means that this is a DEBUG kernel and it is **
> ** unsafe for production use. **
> ** **
> ** If you see this message and you are not debugging **
> ** the kernel, report this immediately to your vendor! **
> ** **
> ** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **
> **********************************************************
And that is done purposely. No DO NOT USE ftrace_vprintk()!!!
I explained why to John.
For you, I made this quick patch. If this works for you, I can make it
into a formal patch. It includes a test use case in do_sys_openat2() to
show the file name and file descriptor. Obviously, that wont be part of
the final patch.
Thoughts?
-- Steve
diff --git a/fs/open.c b/fs/open.c
index b69d6eed67e6..ea19478a2220 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -32,6 +32,7 @@
#include <linux/ima.h>
#include <linux/dnotify.h>
#include <linux/compat.h>
+#include <trace/events/printk.h>
#include "internal.h"
@@ -1127,6 +1128,15 @@ struct file *file_open_root(struct dentry *dentry,
struct vfsmount *mnt,
}
EXPORT_SYMBOL(file_open_root);
+static void do_trace_vprintk(const char *fmt, ...)
+{
+ va_list ap;
+
+ va_start(ap, fmt);
+ trace_vprintk(fmt, ap);
+ va_end(ap);
+}
+
static long do_sys_openat2(int dfd, const char __user *filename,
struct open_how *how)
{
@@ -1141,6 +1151,8 @@ static long do_sys_openat2(int dfd, const char __user
*filename,
if (IS_ERR(tmp))
return PTR_ERR(tmp);
+ do_trace_vprintk("file=%s fd=%d\n", tmp->name, fd);
+
fd = get_unused_fd_flags(how->flags);
if (fd >= 0) {
struct file *f = do_filp_open(dfd, tmp, &op);
diff --git a/include/trace/events/printk.h b/include/trace/events/printk.h
index 13d405b2fd8b..60d9ca21acf9 100644
--- a/include/trace/events/printk.h
+++ b/include/trace/events/printk.h
@@ -31,6 +31,53 @@ TRACE_EVENT(console,
TP_printk("%s", __get_str(msg))
);
+
+#ifndef __FIND_VPRINTK_LEN_H
+#define __FIND_VPRINTK_LEN_H
+/* The header is called multiple times, but this should not be */
+static inline int find_vprintk_len(const char *fmt, va_list args)
+{
+ va_list va;
+ int len;
+
+ va_copy(va, args);
+ len = vsnprintf(NULL, 0, fmt, va);
+ va_end(va);
+ return len + 1;
+}
+#endif
+
+TRACE_EVENT(vprintk,
+ TP_PROTO(const char *fmt, va_list args),
+
+ TP_ARGS(fmt, args),
+
+ TP_STRUCT__entry(
+ __dynamic_array(char, msg, find_vprintk_len(fmt, args))
+ ),
+
+ TP_fast_assign(
+ va_list ap;
+ int len = find_vprintk_len(fmt, args);
+
+ va_copy(ap, args);
+ len = vsnprintf(__get_str(msg), len, fmt, ap);
+ va_end(ap);
+ /*
+ * Each trace entry is printed in a new line.
+ * If the msg finishes with '\n', cut it off
+ * to avoid blank lines in the trace.
+ */
+ if ((len > 0) && (__get_str(msg)[len-1] == '\n'))
+ len -= 1;
+
+ __get_str(msg)[len] = 0;
+ ),
+
+ TP_printk("%s", __get_str(msg))
+);
+
+
#endif /* _TRACE_PRINTK_H */
/* This part must be outside protection */
