Re: [musl] [PATCH v2] add close_range() syscall wrapper

[Alexey Izbyshev <izbyshev@ispras.ru>]

On 2023-09-01 17:58, Natanael Copa wrote:
> close_range() is a syscall present in FreeBSD 8.0 and Linux 5.9. glibc
> 2.34 added a wrapper.
> 
> Expose it under _GNU_SOURCE similar to what GNU libc does. Also expose
> it under _BSD_SOURCE since it is also a FreeBSD function.
> ---
> 
> v2: use syscall without __syscall_ret
> 
>  include/unistd.h        | 3 +++
>  src/linux/close_range.c | 8 ++++++++
>  2 files changed, 11 insertions(+)
>  create mode 100644 src/linux/close_range.c
> 
> diff --git a/include/unistd.h b/include/unistd.h
> index 5bc7f798..d89e3d4c 100644
> --- a/include/unistd.h
> +++ b/include/unistd.h
> @@ -161,6 +161,9 @@ unsigned ualarm(unsigned, unsigned);
>  #define L_INCR 1
>  #define L_XTND 2
>  int brk(void *);
> +#define CLOSE_RANGE_UNSHARE	(1U << 1)
> +#define CLOSE_RANGE_CLOEXEC	(1U << 2)
> +int close_range(unsigned int, unsigned int, int);
>  void *sbrk(intptr_t);
>  pid_t vfork(void);
>  int vhangup(void);
> diff --git a/src/linux/close_range.c b/src/linux/close_range.c
> new file mode 100644
> index 00000000..3f1378a0
> --- /dev/null
> +++ b/src/linux/close_range.c
> @@ -0,0 +1,8 @@
> +#define _GNU_SOURCE
> +#include <unistd.h>
> +#include "syscall.h"
> +
> +int close_range(unsigned int first, unsigned int last, int flags)
> +{
> +	return syscall(SYS_close_range, first, last, flags);
> +}

Regarding FreeBSD, close_range was added not in 8.0, but in 13.0 [1], 
and also backported to 12.2 [2].

Otherwise, this patch looks good to me.

Rich, is it possible to consider close_range wrapper inclusion again? 
Apart from FreeBSD and glibc, bionic has it too. A cursory Debian code 
search shows that close_range libc wrapper can be used at least by 
openssh, libvirt, network-manager, openrc, qemu, lxc, rsyslog packages 
(in addition to CPython that I mentioned ealier).

As for having a fallback in case the syscall is unavailable, I'm not 
aware of anybody implementing it, so I'd expect all close_range users to 
implement their own fallback/error handling. For example, Debian's 
openssh migrated from closefrom to close_range with their own fallback 
because of too aggressive closefrom fallback in glibc[3].

Thanks,
Alexey

[1] 
https://cgit.freebsd.org/src/commit/?h=releng/13.0&id=472ced39efb537374068f06b348fe5dac389c45a
[2] 
https://cgit.freebsd.org/src/commit/?h=releng/12.2&id=a80adba5ab46ba6d44d5abfc9b7f3b6de8afda55
[3] 
https://sources.debian.org/src/openssh/1%3A9.8p1-1/debian/changelog/#L895