Re: [PATCH] ftrace: add an fsync tracer

[fche@redhat.com (Frank Ch. Eigler)]

Arjan van de Ven <arjan@infradead.org> writes:

> [...]
> what is the real need is
> 1) Have a trace point in the source
> 2) Associate a "formatting function" with that point 
>    (which basically transforms the trace parameters to, say, a string)
> 3) A way to turn the trace point on/off.

For 1 and 2, it may be worth considering a plain trace_mark() in
do_sync().  The complication that makes this uglier than a one-liner
is d_path()'s buffer and error handling.

    {
    char *buffer = kzalloc (4096, GFP_KERNEL);
    trace_mark(fsync, "Process %s is calling fsync on %s\n",
                       current->comm,
                       ({char *err = d_path (...);
                         IS_ERR(err) ? "?" : err;}));
    kfree (buffer);
    }

With a bit of extension on the marker front, the allocation could be
made conditional on the marker being enabled.


For 3, the kernel could merge a backend that connects arbitrary
markers to an ftrace (or whatever) buffer.  Several compact prototypes
for the latter exist.


- FChE