> On Nov 17, 2016, at 1:00 PM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote: > > On Thu, Nov 17, 2016 at 04:45:45PM +0000, David Howells wrote: >> One Thousand Gnomes <gnomes@xxxxxxxxxxxxxxxxxxx> wrote: >> >>>> (2) Lightweight stat (AT_STATX_DONT_SYNC): Ask for just those details of >>>> interest, and allow a network fs to approximate anything not of >>>> interest, without going to the server. >>>> >>>> (3) Heavyweight stat (AT_STATX_FORCE_SYNC): Force a network fs to flush >>>> buffers and go to the server, even if it thinks its cached attributes >>>> are up to date. >>> >>> That seems an odd way to do it. Wouldn't it be cleaner and more flexible >>> to give a timestamp of the oldest time you consider acceptable (and >>> obviously passing 0 indicates whatever you have) >> >> Perhaps, though adding 6-argument syscalls is apparently frowned upon. >> >>>> Note that no lstat() equivalent is required as that can be implemented >>>> through statx() with atflag == 0. There is also no fstat() equivalent as >>>> that can be implemented through statx() with filename == NULL and the >>>> relevant fd passed as dfd. >>> >>> and dfd + a name gives you fstatat() ? >> >> Yes. >> >>> The cover note could be clearer on this. >> >> Fixed. >> >>> Should the fields really be split the way they are for times rather than >>> a struct for each one so you can write code generically to handle one of >>> those rather than having to have a 4 way switch statement all the time. >> >> It depends. Doing so leaves 16 bytes of hole in the structure. I could >> ameliorate the wastage by using a union to overlay useful fields in the gaps, >> but that's pretty icky and might be compiler dependent. >> >>> Another attribute that would be nice (but migt need some trivial device >>> layer tweaking) would be STATX_ATTR_VOLATILE for filesystems that will >>> probably evaporate on a reboot. That's useful information for tools like >>> installers and also for sanity checking things like backup paths. >> >> There's a FILE_ATTRIBUTE_TEMPORARY that I could map for windows filesystems >> that could be used with this. >> >>> Remote needs to have clear semantics: is ext4fs over nbd 'remote' for >>> example ? >> >> Hmmm... Interesting question. Probably should. But you could be insane and >> RAID an nbd and a local disk. Further, does NFS over a loopback device to >> nfsd on the same machine qualify as root? What if that's exposing a local fs >> on NBD? Perhaps I should drop 'REMOTE' for now. It sounds like something >> that a GUI filemanager might find interesting, though. > > Sorry, I haven't been paying attention, just popping up for this, but: > "shared" might be a more useful term than "remote". > > A filesystem that may be mounted from more than one system is "shared". > Caching performance and semantics of such a filesystem are more > complicated since the filesystem may change out from under us. This is > what makes e.g. the lightweight/heavyweight stat difference more > interesting in the shared case. > > The filesystem should be able to make that shared/unshared distinction > without knowledge of the storage it's sitting on top of. > > Answering your questions by that criterion: > > - ext4/nbd: not shared > - nfs/lo: shared > > But, it's fine with me to drop any features for now as long as we can > always add them later. Please, please, please, let's get the syscall and basic functionality landed first, and then nit-pick about extensions later. This has been dragging on for _years_ and bike shedded to death. Cheers, Andreas
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