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
