// SPDX-License-Identifier: GPL-2.0-only
/*
 *
 * Misc librarized functions for cmdline poking.
 */
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/ctype.h>
#include <asm/setup.h>

static inline int myisspace(u8 c)
{
        return c <= ' ';        /* Close enough approximation */
}

/**
 * Find a boolean option (like quiet,noapic,nosmp....)
 *
 * @cmdline: the cmdline string
 * @option: option string to look for
 *
 * Returns the position of that @option (starts counting with 1)
 * or 0 on not found.  @option will only be found if it is found
 * as an entire word in @cmdline.  For instance, if @option="car"
 * then a cmdline which contains "cart" will not match.
 */
static int
__cmdline_find_option_bool(const char *cmdline, int max_cmdline_size,
                           const char *option)
{
        char c;
        int pos = 0, wstart = 0;
        const char *opptr = NULL;
        enum {
                st_wordstart = 0,       /* Start of word/after whitespace */
                st_wordcmp,     /* Comparing this word */
                st_wordskip,    /* Miscompare, skip */
        } state = st_wordstart;

        if (!cmdline)
                return -1;      /* No command line */

        /*
         * This 'pos' check ensures we do not overrun
         * a non-NULL-terminated 'cmdline'
         */
        while (pos < max_cmdline_size) {
                c = *(char *)cmdline++;
                pos++;

                switch (state) {
                case st_wordstart:
                        if (!c)
                                return 0;
                        else if (myisspace(c))
                                break;

                        state = st_wordcmp;
                        opptr = option;
                        wstart = pos;
                        fallthrough;

                case st_wordcmp:
                        if (!*opptr) {
                                /*
                                 * We matched all the way to the end of the
                                 * option we were looking for.  If the
                                 * command-line has a space _or_ ends, then
                                 * we matched!
                                 */
                                if (!c || myisspace(c))
                                        return wstart;
                                /*
                                 * We hit the end of the option, but _not_
                                 * the end of a word on the cmdline.  Not
                                 * a match.
                                 */
                        } else if (!c) {
                                /*
                                 * Hit the NULL terminator on the end of
                                 * cmdline.
                                 */
                                return 0;
                        } else if (c == *opptr++) {
                                /*
                                 * We are currently matching, so continue
                                 * to the next character on the cmdline.
                                 */
                                break;
                        }
                        state = st_wordskip;
                        fallthrough;

                case st_wordskip:
                        if (!c)
                                return 0;
                        else if (myisspace(c))
                                state = st_wordstart;
                        break;
                }
        }

        return 0;       /* Buffer overrun */
}

/*
 * Find a non-boolean option (i.e. option=argument). In accordance with
 * standard Linux practice, if this option is repeated, this returns the
 * last instance on the command line.
 *
 * @cmdline: the cmdline string
 * @max_cmdline_size: the maximum size of cmdline
 * @option: option string to look for
 * @buffer: memory buffer to return the option argument
 * @bufsize: size of the supplied memory buffer
 *
 * Returns the length of the argument (regardless of if it was
 * truncated to fit in the buffer), or -1 on not found.
 */
static int
__cmdline_find_option(const char *cmdline, int max_cmdline_size,
                      const char *option, char *buffer, int bufsize)
{
        char c;
        int pos = 0, len = -1;
        const char *opptr = NULL;
        char *bufptr = buffer;
        enum {
                st_wordstart = 0,       /* Start of word/after whitespace */
                st_wordcmp,     /* Comparing this word */
                st_wordskip,    /* Miscompare, skip */
                st_bufcpy,      /* Copying this to buffer */
        } state = st_wordstart;

        if (!cmdline)
                return -1;      /* No command line */

        /*
         * This 'pos' check ensures we do not overrun
         * a non-NULL-terminated 'cmdline'
         */
        while (pos++ < max_cmdline_size) {
                c = *(char *)cmdline++;
                if (!c)
                        break;

                switch (state) {
                case st_wordstart:
                        if (myisspace(c))
                                break;

                        state = st_wordcmp;
                        opptr = option;
                        fallthrough;

                case st_wordcmp:
                        if ((c == '=') && !*opptr) {
                                /*
                                 * We matched all the way to the end of the
                                 * option we were looking for, prepare to
                                 * copy the argument.
                                 */
                                len = 0;
                                bufptr = buffer;
                                state = st_bufcpy;
                                break;
                        } else if (c == *opptr++) {
                                /*
                                 * We are currently matching, so continue
                                 * to the next character on the cmdline.
                                 */
                                break;
                        }
                        state = st_wordskip;
                        fallthrough;

                case st_wordskip:
                        if (myisspace(c))
                                state = st_wordstart;
                        break;

                case st_bufcpy:
                        if (myisspace(c)) {
                                state = st_wordstart;
                        } else {
                                /*
                                 * Increment len, but don't overrun the
                                 * supplied buffer and leave room for the
                                 * NULL terminator.
                                 */
                                if (++len < bufsize)
                                        *bufptr++ = c;
                        }
                        break;
                }
        }

        if (bufsize)
                *bufptr = '\0';

        return len;
}

int cmdline_find_option_bool(const char *cmdline, const char *option)
{
        return __cmdline_find_option_bool(cmdline, COMMAND_LINE_SIZE, option);
}

int cmdline_find_option(const char *cmdline, const char *option, char *buffer,
                        int bufsize)
{
        return __cmdline_find_option(cmdline, COMMAND_LINE_SIZE, option,
                                     buffer, bufsize);
}