Messages in this thread | | | Date | Thu, 22 Feb 2007 15:11:31 -0500 | From | Peter Staubach <> | Subject | Re: [PATCH] update ctime and mtime for mmaped write |
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Miklos Szeredi wrote: >>>>>>> +int set_page_dirty_mapping(struct page *page); >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>> This aspect of the design seems intrusive to me. I didn't see a strong >>>>>> reason to introduce new versions of many of the routines just to handle >>>>>> these semantics. What motivated this part of your design? Why the new >>>>>> _mapping versions of routines? >>>>>> >>>>>> >>>>>> >>>>> Because there's no way to know inside the set_page_dirty() functions >>>>> if the dirtying comes from a memory mapping or from a modification >>>>> through a normal write(). And they have different semantics, for >>>>> write() the modification times are updated immediately. >>>>> >>>>> >>>> Perhaps I didn't understand what page_mapped() does, but it does seem to >>>> have the right semantics as far as I could see. >>>> >>>> >>> The problems will start, when you have a file that is both mapped and >>> modified with write(). Then the dirying from the write() will set the >>> flag, and that will have undesirable consequences. >>> >> I don't think that I quite follow the logic. The dirtying from write() >> will set the flag, but then the mtime will get updated and the flag will >> be cleared by the hook in file_update_time(). Right? >> > > Take this example: > > fd = open() > addr = mmap(.., fd) > write(fd, ...) > close(fd) > sleep(100) > msync(addr,...) > munmap(addr) > > The file times will be updated in write(), but with your patch, the > bit in the mapping will also be set. > > Then in msync() the file times will be updated again, which is wrong, > since the memory was _not_ modified through the mapping.
This is correct. I have updated my proposed patch to include the clearing of AS_MCTIME in the routine which updates the mtime field. I haven't reposted it yet until I complete testing of the new resulting system. I anticipate doing this later today.
Thanx..
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