This documents close_range(2) based on information in 278a5fbaed89dacd04e9d052f4594ffd0e0585de and 60997c3d45d9a67daf01c56d805ae4fec37e0bd8. Signed-off-by: Stephen Kitt <steve@xxxxxxx> --- man2/close_range.2 | 112 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 112 insertions(+) create mode 100644 man2/close_range.2 diff --git a/man2/close_range.2 b/man2/close_range.2 new file mode 100644 index 000000000..62167d9b0 --- /dev/null +++ b/man2/close_range.2 @@ -0,0 +1,112 @@ +.\" Copyright (c) 2020 Stephen Kitt <steve@xxxxxxx> +.\" +.\" %%%LICENSE_START(VERBATIM) +.\" Permission is granted to make and distribute verbatim copies of this +.\" manual provided the copyright notice and this permission notice are +.\" preserved on all copies. +.\" +.\" Permission is granted to copy and distribute modified versions of this +.\" manual under the conditions for verbatim copying, provided that the +.\" entire resulting derived work is distributed under the terms of a +.\" permission notice identical to this one. +.\" +.\" Since the Linux kernel and libraries are constantly changing, this +.\" manual page may be incorrect or out-of-date. The author(s) assume no +.\" responsibility for errors or omissions, or for damages resulting from +.\" the use of the information contained herein. The author(s) may not +.\" have taken the same level of care in the production of this manual, +.\" which is licensed free of charge, as they might when working +.\" professionally. +.\" +.\" Formatted or processed versions of this manual, if unaccompanied by +.\" the source, must acknowledge the copyright and authors of this work. +.\" %%%LICENSE_END +.\" +.TH CLOSE_RANGE 2 2020-12-08 "Linux" "Linux Programmer's Manual" +.SH NAME +close_range \- close all file descriptors in a given range +.SH SYNOPSIS +.nf +.B #include <linux/close_range.h> +.PP +.BI "int close_range(int " first ", int " last ", unsigned int " flags ); +.fi +.SH DESCRIPTION +The +.BR close_range () +system call closes all open file descriptors from +.I first +to +.IR last +(included). +.PP +Errors closing a given file descriptor are currently ignored. +.PP +.I flags +can be set to +.B CLOSE_RANGE_UNSHARE +to unshare the range of file descriptors from any other processes, +.I instead +of closing them. +.SH RETURN VALUE +On success, +.BR close_range () +return 0. +On error, \-1 is returned and +.I errno +is set to indicate the cause of the error. +.SH ERRORS +.TP +.B EINVAL +.I flags +is not valid, or +.I first +is greater than +.IR last . +.TP +.B EMFILE +The per-process limit on the number of open file descriptors has been reached +(see the description of +.BR RLIMIT_NOFILE +in +.BR getrlimit (2)). +.TP +.B ENOMEM +Insufficient kernel memory was available. +.SH VERSIONS +.BR close_range () +first appeared in Linux 5.9. +.SH CONFORMING TO +.BR close_range () +is available on Linux and FreeBSD. +.SH NOTES +Currently, there is no glibc wrapper for this system call; call it using +.BR syscall (2). +.SH USE CASES +.\" 278a5fbaed89dacd04e9d052f4594ffd0e0585de +.\" 60997c3d45d9a67daf01c56d805ae4fec37e0bd8 +.SS Closing file descriptors before exec +File descriptors can be closed safely using +.PP +.in +4n +.EX +/* we don't want anything past stderr here */ +close_range(3, ~0U, CLOSE_RANGE_UNSHARE); +execve(....); +.EE +.in +.PP +.SS Closing all open file descriptors +This is commonly implemented (on Linux) by listing open file +descriptors in +.B /proc/self/fd/ +and calling +.BR close (2) +on each one. +.BR close_range () +can take care of this without requiring +.B /proc +and with a single system call, which provides significant performance +benefits. +.SH SEE ALSO +.BR close (2) base-commit: b5dae3959625f5ff378e9edf9139057d1c06bb55 -- 2.20.1
