Re: [RFC PATCH] getvalues(2) prototype

[Miklos Szeredi <mszeredi@xxxxxxxxxx>]

On Tue, Mar 22, 2022 at 8:27 PM Miklos Szeredi <mszeredi@xxxxxxxxxx> wrote:
>
> Add a new userspace API that allows getting multiple short values in a
> single syscall.

Attaching a test program that allows arbitrary queries.

Thanks,
Miklos

#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include <fcntl.h>
#include <err.h>
#include <stdint.h>
#include <sys/uio.h>

struct name_val {
	const char *name;	/* in */
	struct iovec value_in;	/* in */
	struct iovec value_out;	/* out */
	uint32_t error;		/* out */
	uint32_t reserved;
};


int getvalues(int dfd, const char *path, struct name_val *vec, size_t num,
	      unsigned int flags)
{
	return syscall(451, dfd, path, vec, num, flags);
}

int main(int argc, char *argv[])
{
	char *s, buf[4096];
	int res, i, o, num = argc - 2;
	struct name_val nvs[256] = {};

	if (argc < 3)
		errx(1, "usage: %s path name [...]", argv[0]);
	if (num > 256)
		errx(1, "too many arguments");

	for (i = 0; i < num; i++)
		nvs[i].name = argv[i + 2];

	nvs[0].value_in.iov_base = buf;
	nvs[0].value_in.iov_len = sizeof(buf);

	res = getvalues(AT_FDCWD, argv[1], nvs, num, 0);
	if (res == -1)
		err(1, NULL);

	num = res;
	for (i = 0; i < num; i++) {
		printf("[%s] = ", nvs[i].name);
		res = nvs[i].error;
		if (res) {
			printf(" ERROR: %s (%i)\n", strerror(res), res);
		} else {
			res = nvs[i].value_out.iov_len;
			s = nvs[i].value_out.iov_base;

			for (o = 0; o < res; o += strlen(s + o) + 1)
				printf("\"%.*s\" ", res - o, s + o);

			printf("(len=%i)\n", res);
		}
	}
	return 0;
}