Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1945949AbXBVHtu (ORCPT ); Thu, 22 Feb 2007 02:49:50 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1945946AbXBVHtt (ORCPT ); Thu, 22 Feb 2007 02:49:49 -0500 Received: from mail-gw3.sa.ew.hu ([212.108.200.82]:39387 "EHLO mail-gw3.sa.ew.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932730AbXBVHtt (ORCPT ); Thu, 22 Feb 2007 02:49:49 -0500 To: akpm@linux-foundation.org CC: staubach@redhat.com, hugh@veritas.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org In-reply-to: <20070221202615.a0a167f4.akpm@linux-foundation.org> (message from Andrew Morton on Wed, 21 Feb 2007 20:26:15 -0800) Subject: Re: [PATCH] update ctime and mtime for mmaped write References: <20070221202615.a0a167f4.akpm@linux-foundation.org> Message-Id: From: Miklos Szeredi Date: Thu, 22 Feb 2007 08:49:12 +0100 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2089 Lines: 47 > On Wed, 21 Feb 2007 18:51:52 +0100 Miklos Szeredi wrote: > > > This patch makes writing to shared memory mappings update st_ctime and > > st_mtime as defined by SUSv3: > > > > The st_ctime and st_mtime fields of a file that is mapped with > > MAP_SHARED and PROT_WRITE shall be marked for update at some point > > in the interval between a write reference to the mapped region and > > the next call to msync() with MS_ASYNC or MS_SYNC for that portion > > of the file by any process. If there is no such call and if the > > underlying file is modified as a result of a write reference, then > > these fields shall be marked for update at some time after the > > write reference. > > > > A new address_space flag is introduced: AS_CMTIME. This is set each > > time a page is dirtied through a userspace memory mapping. This > > includes write accesses via get_user_pages(). > > > > Note, the flag is set unconditionally, even if the page is already > > dirty. This is important, because the page might have been dirtied > > earlier by a non-mmap write. > > > > This flag is checked in msync() and __fput(), and if set, the file > > times are updated and the flag is cleared > > > > The flag is also cleared, if the time update is triggered by a normal > > write. This is not mandated by the standard, but seems to be a sane > > thing to do. > > Why is the flag checked in __fput()? It's because of this bit in the standard: If there is no such call and if the underlying file is modified as a result of a write reference, then these fields shall be marked for update at some time after the write reference. It could be done in munmap/mremap, but it seemed more difficult to track down all the places where the vma is removed. But yes, that may be a nicer solution. Miklos - 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/