From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from top.free-electrons.com ([176.31.233.9] helo=mail.free-electrons.com) by merlin.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1WKoFY-00024W-W6 for linux-mtd@lists.infradead.org; Tue, 04 Mar 2014 12:15:09 +0000 Date: Tue, 4 Mar 2014 09:14:47 -0300 From: Ezequiel Garcia To: Artem Bityutskiy Subject: Re: [PATCH] UBI: block: Use ENOSYS as return value when CONFIG_UBIBLOCK=n Message-ID: <20140304121446.GA8826@localhost> References: <1393930663-8737-1-git-send-email-ezequiel.garcia@free-electrons.com> <1393933791.3412.208.camel@sauron.fi.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1393933791.3412.208.camel@sauron.fi.intel.com> Cc: linux-mtd@lists.infradead.org List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, Mar 04, 2014 at 01:49:51PM +0200, Artem Bityutskiy wrote: > On Tue, 2014-03-04 at 07:57 -0300, Ezequiel Garcia wrote: > > In order to have a way of distinguishing an invalid ioctl from a > > not supported (but otherwise valid) ioctl, this commit changes the > > return value of the ioctl stubs from ENOTTY to ENOSYS. > > Sounds logical, no objections, except it is curious if this is something > you invented or this is a general rule in the Linux kernel? If it is, > may be you can point to some discussions, or give some example or other > source of this knowledge? I just want to be educated a bit. Thanks! > Yes, I think it's a pretty extended kernel practice to return -ENOSYS when a function is not built or either not implemented. A good number of headers in include/linux/ use -ENOSYS as the return value for the !CONFIG_FEATURE stubs. $ git grep ENOSYS include/linux/ | wc -l 172 And of course, the syscall ABI returns -ENOSYS for unimplemented system calls. -- Ezequiel García, Free Electrons Embedded Linux, Kernel and Android Engineering http://free-electrons.com