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SubjectRe: [PATCH 1/2] Trace code and documentation
On Fri, 14 Sep 2007 18:08:40 -0700 Andrew Morton wrote:

> > Trace - Provides tracing primitives
> >
> > ...
> >
> > +config TRACE
> > + bool "Trace setup and control"
> > + select RELAY
> > + select DEBUG_FS
> > + help
> > + This option provides support for the setup, teardown and control
> > + of tracing channels from kernel code. It also provides trace
> > + information and control to userspace via a set of debugfs control
> > + files. If unsure, say N.
> > +
>
> select is evil - you really want to avoid using it.

I checked when I reviewed(?) this patch. There are a few other
places that select also (IIRC, the blktrace code does), but most of
them use depends on.

> The problem is where you select a symbol whose dependencies aren't met.
> Kconfig resolves this incompatibility by just not selecting the thing you
> wanted, iirc. So your CONFIG_SYSFS=n, CONFIG_TRACE=y kernel won't build.
>
> > +/*
> > + * Based on blktrace code, Copyright (C) 2006 Jens Axboe <axboe@suse.de>
>
> So can we migrate blktrace to using this?

> > +static ssize_t sub_size_read(struct file *filp, char __user *buffer,
> > + size_t count, loff_t *ppos)
> > +{
> > + struct trace_info *trace = filp->private_data;
> > + char buf[32];
> > +
> > + snprintf(buf, sizeof(buf), "%u\n",
> > + (unsigned int)trace->rchan->subbuf_size);
>
> Use %tu to print a size_t, rather than the typecast.

Eh?
Use %zu to print a size_t. Use %tu to print a ptrdiff_t.


---
~Randy
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