Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756926AbbKRU2m (ORCPT ); Wed, 18 Nov 2015 15:28:42 -0500 Received: from mail-oi0-f43.google.com ([209.85.218.43]:36854 "EHLO mail-oi0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753403AbbKRU2j (ORCPT ); Wed, 18 Nov 2015 15:28:39 -0500 MIME-Version: 1.0 Reply-To: rajatxjain@gmail.com In-Reply-To: <20151113063103.GO22011@ZenIV.linux.org.uk> References: <20151113063103.GO22011@ZenIV.linux.org.uk> Date: Wed, 18 Nov 2015 12:28:38 -0800 Message-ID: Subject: Re: Anonymous inode cleanup? From: Rajat Jain To: Al Viro Cc: linux-fsdevel@vger.kernel.org, Davide Libenzi , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2630 Lines: 68 Hi Al, Thanks a lot! That was very helpful. I have one follow up question though. On Thu, Nov 12, 2015 at 10:31 PM, Al Viro wrote: > On Thu, Nov 12, 2015 at 09:43:00PM -0800, Rajat Jain wrote: >> Hello, >> >> I'm writing a module that wants to get anonymous fd [using >> anon_inode_getfd()] and my code looks like this: >> >> fd = anon_inode_getfd(...) >> if (fd < 0) >> return -EINVAL; >> >> if (foobar_fail()) { >> /* undo everything */ >> return -EINVAL; >> } >> >> My question is that in case of a failure after the anon_inode_getfd(), >> I want to cleanup and undo whatever needs to be done w.r.t. anodnymous >> fd I just allocated. (May be put a reference, or return the fd to the >> free pool or whatever). Can some one please let me know what cleanup >> needs to be done? >> >> However neither I see a cleanup function, nor I see any of the drivers >> attempting >> to free the fd in case of failure. > > You can't. As soon as it's in descriptor table, you'd better be *done* > with it. No "I need more setup done", no "I just need to do one final > check" - the moment it hits the descriptor table, another thread might > be issuing syscalls on it. Including dup2(), so there's no way to take > it back. Moreover, another thread might've done dup2() over your > descriptor, so you can't even decide to close the one you'd just installed. > Yes, even in cases when the failed action would be to report the resulting > descriptor to userland. Generally you should try to return descriptors to > userland only via the syscall return value. > > _If_ you are returning them via a sucky API, the right sequence is > reserve the descriptor(s) > set the file(s) up > fill whatever structure you'll be using to report descriptors to > userland and copy it to userland memory If this step fails, what is the cleanup needed for "set the files up" anon_inode_getfile() step? is it fput()? Thanks, Rajat > use fd_install() to put files into descriptor table. > > See e.g. fs/pipe.c and look for pipe2 in there for example of dealing with > such APIs. > > "Set the file up" primitive in case of anon_inode is anon_inode_getfile(); > grep and you shall see... > > Again, fd_install() is the equivalent of hitting "send" - there's no way > to make what you've published disappear. It's the point of no return. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/