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. --b. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
