On Mon, Aug 27, 2018 at 08:07:35PM -0500, Steve French wrote: > On Mon, Aug 27, 2018 at 7:45 PM Theodore Y. Ts'o <tytso@xxxxxxx> wrote: > > > > On Mon, Aug 27, 2018 at 11:21:43AM -0700, Matthew Wilcox wrote: > > > On Mon, Aug 27, 2018 at 10:05:31AM -0700, Jeremy Allison wrote: > > > > I can't think of a *single* case where a stream adds more > > > > utility than an EA used in the same case. > > > > > > > > I don't want theoretical "well it would be nice if..", > > > > I want clear "we couldn't have done it any other way" > > > > kinds of things. > > > > > > I started this thread with such an example. The fs-verity patch proposed > > > wants to store hundreds of megabytes of data associated with a particular > > > file. The current solution is to append it to the end of the data then > > > magic to set i_size lower but not remove the data from the file like a > > > truncate would. Then more magic to read that data. > > > > Sure, but so what? The Merkle Tree only needs to be read by the > > kernel, and we only need to install the fs-verity data once. And > > putting it at the end of the file works just fine. Theoretically we > > could do it other ways, but this is almost certainly easier and > > cleaner than if we had to open a streams file from kernel code. > > > > Doing it using streams would actually be *harder* and is only of use > > for people who like more structured designs. But to be clear, this is > > *not* something I'm asking for as one of the original designers of > > fs-verity. > > Given that streams need to be read to backup Macs and Windows > (and for a few features of these servers mentioned earlier) > and would be exposed in ntfs (and SMB3 remotely) locally on Linux, > seems useful to me to have some consistent way to open and read > them on Linux even if we don't want to generalize it to other local fs. > The protocol supports it fine (just a file with a reserved character > ':' in it) but a little tricky to avoid name conflict with posix ':' > in filenames This sounds like a case for a couple of ioctls. One to enumerate the streams on an open fd, one to open a given stream name on an open fd.
