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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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