On Wed, Jun 24, 2020 at 01:37:52PM +0100, Robin Murphy wrote:
> On 2020-06-24 12:41, Andrzej Hajda wrote:
> > Many resource acquisition functions return error value encapsulated in
> > pointer instead of integer value. To simplify coding we can use macro
> > which will accept both types of error.
> > With this patch user can use:
> > probe_err(dev, ptr, ...)
> > instead of:
> > probe_err(dev, PTR_ERR(ptr), ...)
> > Without loosing old functionality:
> > probe_err(dev, err, ...)
>
> Personally I'm not convinced that simplification has much value, and I'd
> say it *does* have a significant downside. This:
>
> if (IS_ERR(x))
> do_something_with(PTR_ERR(x));
>
> is a familiar and expected pattern when reading/reviewing code, and at a
> glance is almost certainly doing the right thing. If I see this, on the
> other hand:
>
> if (IS_ERR(x))
> do_something_with(x);
>
> my immediate instinct is to be suspicious, and now I've got to go off
> and double-check that if do_something_with() really expects a pointer
> it's also robust against PTR_ERR values. Off-hand I can't think of any
> APIs that work that way in the areas with which I'm familiar, so it
> would be a pretty unusual and non-obvious thing.
I second this. Furthermore, the hidden cast to long means that we'll
leak pointer values if one happens to pass a real pointer to this
function.
> Furthermore, an error helper that explicitly claims to accept "pointer
> type" values seems like it could easily lead to misunderstandings like this:
>
> int init_my_buffer(struct my_device *d)
> {
> d->buffer = kzalloc(d->buffer_size, GFP_KERNEL);
> return probe_err(d->dev, d->buffer, "failed to init buffer\n");
> }
>
> and allowing that to compile without any hint of an error seems a
> little... unfair.
>
> Robin.
>
> > Signed-off-by: Andrzej Hajda <a.hajda@xxxxxxxxxxx>
> > ---
> > drivers/base/core.c | 25 ++-----------------------
> > include/linux/device.h | 25 ++++++++++++++++++++++++-
> > 2 files changed, 26 insertions(+), 24 deletions(-)
> >
> > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > index 2a96954d5460..df283c62d9c0 100644
> > --- a/drivers/base/core.c
> > +++ b/drivers/base/core.c
> > @@ -3953,28 +3953,7 @@ define_dev_printk_level(_dev_info, KERN_INFO);
> >
> > #endif
> >
> > -/**
> > - * probe_err - probe error check and log helper
> > - * @dev: the pointer to the struct device
> > - * @err: error value to test
> > - * @fmt: printf-style format string
> > - * @...: arguments as specified in the format string
> > - *
> > - * This helper implements common pattern present in probe functions for error
> > - * checking: print message if the error is not -EPROBE_DEFER and propagate it.
> > - * In case of -EPROBE_DEFER it sets defer probe reason, which can be checked
> > - * later by reading devices_deferred debugfs attribute.
> > - * It replaces code sequence:
> > - * if (err != -EPROBE_DEFER)
> > - * dev_err(dev, ...);
> > - * return err;
> > - * with
> > - * return probe_err(dev, err, ...);
> > - *
> > - * Returns @err.
> > - *
> > - */
> > -int probe_err(const struct device *dev, int err, const char *fmt, ...)
> > +int __probe_err(const struct device *dev, int err, const char *fmt, ...)
> > {
> > struct va_format vaf;
> > va_list args;
> > @@ -3992,7 +3971,7 @@ int probe_err(const struct device *dev, int err, const char *fmt, ...)
> >
> > return err;
> > }
> > -EXPORT_SYMBOL_GPL(probe_err);
> > +EXPORT_SYMBOL_GPL(__probe_err);
> >
> > static inline bool fwnode_is_primary(struct fwnode_handle *fwnode)
> > {
> > diff --git a/include/linux/device.h b/include/linux/device.h
> > index 40a90d9bf799..22d3c3d4f461 100644
> > --- a/include/linux/device.h
> > +++ b/include/linux/device.h
> > @@ -965,7 +965,30 @@ void device_links_supplier_sync_state_pause(void);
> > void device_links_supplier_sync_state_resume(void);
> >
> > extern __printf(3, 4)
> > -int probe_err(const struct device *dev, int err, const char *fmt, ...);
> > +int __probe_err(const struct device *dev, int err, const char *fmt, ...);
> > +
> > +/**
> > + * probe_err - probe error check and log helper
> > + * @dev: the pointer to the struct device
> > + * @err: error value to test, can be integer or pointer type
> > + * @fmt: printf-style format string
> > + * @...: arguments as specified in the format string
> > + *
> > + * This helper implements common pattern present in probe functions for error
> > + * checking: print message if the error is not -EPROBE_DEFER and propagate it.
> > + * In case of -EPROBE_DEFER it sets defer probe reason, which can be checked
> > + * later by reading devices_deferred debugfs attribute.
> > + * It replaces code sequence:
> > + * if (err != -EPROBE_DEFER)
> > + * dev_err(dev, ...);
> > + * return err;
> > + * with
> > + * return probe_err(dev, err, ...);
> > + *
> > + * Returns @err.
> > + *
> > + */
> > +#define probe_err(dev, err, args...) __probe_err(dev, (long)(err), args)
> >
> > /* Create alias, so I can be autoloaded. */
> > #define MODULE_ALIAS_CHARDEV(major,minor) \
> >
--
Regards,
Laurent Pinchart
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