From mboxrd@z Thu Jan 1 00:00:00 1970 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: owner-linux-mm@kvack.org Return-Path: 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 List-ID: > 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org