kernel command line parser

gistfile1.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <string.h>

static int xread(int fd, void* buf, size_t len)
{
    int r;

    do {
        r = read(fd, buf, len);
    } while (r < 0 && errno == EINTR);

    return r;
}

static int proc_read(const char* filename, char* buf, size_t size)
{
    int len = 0;

    int fd = open(filename, O_RDONLY);
    if (fd < 0) {
        return len;
    }

    len = xread(fd, buf, size - 1);
    close(fd);

    buf[len > 0 ? len : 0] = 0;
    return len;
}

static int parse_cmdline(const char* opt, char* buf, size_t size)
{
    char cmdline[1024];

    if (proc_read("/proc/cmdline", cmdline, sizeof(cmdline)) > 0) {
        struct {
            const char* delim;
            char* tok, *str, *saveptr;
        } ctx[2] = { { " ", NULL, cmdline, NULL }, { "=", NULL, NULL, NULL } };

        for (; (ctx[0].tok = strtok_r(ctx[0].str, ctx[0].delim, &ctx[0].saveptr)) != NULL;
             ctx[0].str = ctx[0].saveptr) {
            ctx[1].str = ctx[0].tok;

            for (; (ctx[1].tok = strtok_r(ctx[1].str, ctx[1].delim, &ctx[1].saveptr)) != NULL;
                 ctx[1].str = ctx[1].saveptr) {
                if (!strncmp(opt, ctx[1].tok, strlen(opt))) {
                    char* val = strtok_r(ctx[1].saveptr, ctx[1].delim, &ctx[1].saveptr);

                    if (buf) {
                        buf[val ? size - 1 : 0] = 0;

                        if (val) {
                            strncpy(buf, val, size - 1);
                        }
                    }

                    return 1;
                }
            }
        }
    }

    return 0;
}

int main()
{
    int i;
    char buf[1024];
    const char* opts[] = { "root", "splash", "debug" };

    for (i = 0; i < sizeof(opts) / sizeof(*opts); i++) {
        if (parse_cmdline(opts[i], buf, sizeof(buf)) > 0) {
            printf("%s=%s\n", opts[i], buf[0] > 0 ? buf : "N/A");
        }
    }

    exit(EXIT_SUCCESS);
}