Messages in this thread | | | Date | Thu, 10 Jan 2008 18:56:07 +0300 | From | "Anton Salikhmetov" <> | Subject | Re: [PATCH][RFC][BUG] updating the ctime and mtime time stamps in msync() |
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2008/1/10, Rik van Riel <riel@redhat.com>: > On Thu, 10 Jan 2008 13:53:59 +0300 > "Anton Salikhmetov" <salikhmetov@gmail.com> wrote: > > > Indeed, if msync() is called with MS_SYNC an explicit sync is > > triggered, and Rik's suggestion would work. However, the POSIX > > standard requires a call to msync() with MS_ASYNC to update the > > st_ctime and st_mtime stamps too. No explicit sync of the inode data > > is triggered in the current implementation of msync(). Hence Rik's > > suggestion would fail to satisfy POSIX in the latter case. > > Since your patch is already changing msync(), has it occurred > to you that your patch could change msync() to do the right > thing?
No, not quite. Peter Staubach mentioned an issue in my solution:
>>>
> The patch adds a call to the file_update_time() function to change > the file metadata before syncing. The patch also contains > substantial code cleanup: consolidated error check > for function parameters, using the PAGE_ALIGN() macro instead of > "manual" alignment check, improved readability of the loop, > which traverses the process memory regions, updated comments. > >
These changes catch the simple case, where the file is mmap'd, modified via the mmap'd region, and then an msync is done, all on a mostly quiet system.
However, I don't see how they will work if there has been something like a sync(2) done after the mmap'd region is modified and the msync call. When the inode is written out as part of the sync process, I_DIRTY_PAGES will be cleared, thus causing a miss in this code.
The I_DIRTY_PAGES check here is good, but I think that there needs to be some code elsewhere too, to catch the case where I_DIRTY_PAGES is being cleared, but the time fields still need to be updated.
<<<
So I'm working on my next solution for this bug now.
> > -- > All rights reversed. >
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