On Tue, May 21, 2019 at 03:10:11PM +0200, Florian Weimer wrote: > * Christian Brauner: > > >> Solaris has an fdwalk function: > >> > >> <https://docs.oracle.com/cd/E88353_01/html/E37843/closefrom-3c.html> > >> > >> So a different way to implement this would expose a nextfd system call > > > > Meh. If nextfd() then I would like it to be able to: > > - get the nextfd(fd) >= fd > > - get highest open fd e.g. nextfd(-1) > > The highest open descriptor isn't istering for fdwalk because nextfd > would just fail. Sure. I was thinking about other usecases. For example, sometimes in userspace you want to do the following: save_fd = dup(fd, <well-known-number-at-the-end-of-the-range); close_range(3, (save_fd - 1)); Which brings me to another point. So even if we don't do close_range() I would like libc to maybe give us something like close_range() for such scenarios. > > > But then I wonder if nextfd() needs to be a syscall and isn't just > > either: > > fcntl(fd, F_GET_NEXT)? > > or > > prctl(PR_GET_NEXT)? > > I think the fcntl route is a bit iffy because you might need it to get > the *first* valid descriptor. > > >> to userspace, so that we can use that to implement both fdwalk and > >> closefrom. But maybe fdwalk is just too obscure, given the existence of > >> /proc. > > > > Yeah we probably don't need fdwalk. > > Agreed. Just wanted to bring it up for completeness. I certainly don't > want to derail the implementation of close_range. > > Thanks, > Florian
