* Christian Brauner:
+/**
- __close_range() - Close all file descriptors in a given range.
- @fd: starting file descriptor to close
- @max_fd: last file descriptor to close
- This closes a range of file descriptors. All file descriptors
- from @fd up to and including @max_fd are closed.
- */
+int __close_range(struct files_struct *files, unsigned fd, unsigned max_fd) +{
- unsigned int cur_max;
- if (fd > max_fd)
return -EINVAL;
- rcu_read_lock();
- cur_max = files_fdtable(files)->max_fds;
- rcu_read_unlock();
- /* cap to last valid index into fdtable */
- if (max_fd >= cur_max)
max_fd = cur_max - 1;
- while (fd <= max_fd)
__close_fd(files, fd++);
- return 0;
+}
This seems rather drastic. How long does this block in kernel mode? Maybe it's okay as long as the maximum possible value for cur_max stays around 4 million or so.
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 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.
I'll happily implement closefrom on top of close_range in glibc (plus fallback for older kernels based on /proc—with an abort in case that doesn't work because the RLIMIT_NOFILE hack is unreliable unfortunately).
Thanks, Florian