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Date: Thu, 13 Oct 2016 12:29:44 +0200 From: Arnd Bergmann <arnd@...db.de> To: Nicolai Stange <nicstange@...il.com> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Rajneesh Bhardwaj <rajneesh.bhardwaj@...el.com>, Darren Hart <dvhart@...ux.intel.com>, linux-kernel@...r.kernel.org Subject: Re: [PATCH 1/2] debugfs: improve DEFINE_DEBUGFS_ATTRIBUTE for !CONFIG_DEBUGFS_FS On Thursday, October 13, 2016 11:59:54 AM CEST Nicolai Stange wrote: > > > > +ssize_t debugfs_attr_read(struct file *file, char __user *buf, > > + size_t len, loff_t *ppos); > > +ssize_t debugfs_attr_write(struct file *file, const char __user *buf, > > + size_t len, loff_t *ppos); > > + > > +#define DEFINE_DEBUGFS_ATTRIBUTE(__fops, __get, __set, __fmt) \ > > +static int __fops ## _open(struct inode *inode, struct file *file) \ > > +{ \ > > + __simple_attr_check_format(__fmt, 0ull); \ > > + return simple_attr_open(inode, file, __get, __set, __fmt); \ > > +} \ > > +static const struct file_operations __fops = { \ > > + .owner = THIS_MODULE, \ > > + .open = __fops ## _open, \ > > + .release = simple_attr_release, \ > > + .read = debugfs_attr_read, \ > > + .write = debugfs_attr_write, \ > > This depends on GCC dead code elimination to always work for this > situation, otherwise we'd get undefined references to > debugfs_attr_read/write(), right? Correct. > In order to avoid having to test your patch against all those older > versions of GCC, can we have a safety net here and define some dummy > debugfs_attr_read/write() for the !CONFIG_DEBUGFS case? The question of dead-code elimination in older gcc versions comes up occasionally, and I think all versions that are able to build the kernel these days get this right all the time, otherwise any code using IS_ENABLED() helpers to control the calling of external interfaces would be broken. We could probably use that macro here if you think that's better and do: static const struct file_operations __fops = { .owner = THIS_MODULE, .open = IS_ENABLED(CONFIG_DEBUGFS_FS) ? __fops ## _open : NULL, ... > If nothing else, it would IMHO make the !CONFIG_DEBUGFS case more > understandable because one had not to figure out that this actually > relies on dead code elimination to work. Sure, that's fine. Can you do the new version of that patch with the change then? Arnd
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