Re: [PATCH] Implement leftpad syscall

Michael Kerrisk (man-pages)
2016-03-31T22:46:38Z

On 04/01/2016 11:33 AM, Richard Weinberger wrote:
> From: David Gstir <david@sigma-star.at>
>
> Implement the leftpad() system call such that userspace,
> especially node.js applications, can in the near future directly
> use it and no longer depend on fragile npm packages.

Works can't express the importance of adding this system call!
Thanks so much for proposing and implementing it!

Acked-by: Michael Kerrisk <mtk.manpages@gmail.com>

Cheers,

Michael

> Signed-off-by: David Gstir <david@sigma-star.at>
> Signed-off-by: Richard Weinberger <richard@nod.at>
> ---
> arch/x86/entry/syscalls/syscall_64.tbl | 1 +
> include/linux/syscalls.h | 1 +
> kernel/sys.c | 35 ++++++++++++++++++++++++++++++++++
> kernel/sys_ni.c | 1 +
> 4 files changed, 38 insertions(+)
>
> diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
> index cac6d17..f287712 100644
> --- a/arch/x86/entry/syscalls/syscall_64.tbl
> +++ b/arch/x86/entry/syscalls/syscall_64.tbl
> @@ -335,6 +335,7 @@
> 326 common copy_file_range sys_copy_file_range
> 327 64 preadv2 sys_preadv2
> 328 64 pwritev2 sys_pwritev2
> +329 common leftpad sys_leftpad
>
> #
> # x32-specific system call numbers start at 512 to avoid cache impact
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index d795472..a0850bb 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -898,4 +898,5 @@ asmlinkage long sys_copy_file_range(int fd_in, loff_t __user *off_in,
>
> asmlinkage long sys_mlock2(unsigned long start, size_t len, int flags);
>
> +asmlinkage long sys_leftpad(char *str, char pad, char *dst, size_t dst_len);
> #endif
> diff --git a/kernel/sys.c b/kernel/sys.c
> index cf8ba54..e42d972 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -2432,3 +2432,38 @@ COMPAT_SYSCALL_DEFINE1(sysinfo, struct compat_sysinfo __user *, info)
> return 0;
> }
> #endif /* CONFIG_COMPAT */
> +
> +
> +SYSCALL_DEFINE4(leftpad, char *, src, char, pad, char *, dst, size_t, dst_len)
> +{
> + char *buf;
> + long ret;
> + size_t len = strlen_user(src);
> + size_t pad_len = dst_len - len;
> +
> + if (dst_len <= len || dst_len > 4096) {
> + return -EINVAL;
> + }
> +
> + buf = kmalloc(dst_len, GFP_KERNEL);
> + if (!buf)
> + return -ENOMEM;
> +
> + memset(buf, pad, pad_len);
> + ret = copy_from_user(buf + pad_len, src, len);
> + if (ret) {
> + ret = -EFAULT;
> + goto out;
> + }
> +
> + ret = copy_to_user(dst, buf, dst_len);
> + if (ret) {
> + ret = -EFAULT;
> + goto out;
> + }
> +
> + ret = pad_len;
> +out:
> + kfree(buf);
> + return ret;
> +}
> diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
> index 2c5e3a8..262608d 100644
> --- a/kernel/sys_ni.c
> +++ b/kernel/sys_ni.c
> @@ -175,6 +175,7 @@ cond_syscall(sys_setfsgid);
> cond_syscall(sys_capget);
> cond_syscall(sys_capset);
> cond_syscall(sys_copy_file_range);
> +cond_syscall(sys_leftpad);
>
> /* arch-specific weak syscall entries */
> cond_syscall(sys_pciconfig_read);
>

--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/