* 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
