dmesg.c

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/*
 * Copyright (C) 2026 Michael Brown <mbrown@fensystems.co.uk>.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 *
 * You can also choose to distribute this program under the terms of
 * the Unmodified Binary Distribution Licence (as given in the file
 * COPYING.UBDL), provided that you have satisfied its requirements.
 */
 
FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
FILE_SECBOOT ( PERMITTED );
 
#include <errno.h>
#include <ipxe/ansiesc.h>
#include <ipxe/settings.h>
#include <ipxe/console.h>
 
/** @file
 *
 * In-memory ring buffer console
 *
 */
 
/* Set default console usage if applicable */
#if ! ( defined ( CONSOLE_DMESG ) && CONSOLE_EXPLICIT ( CONSOLE_DMESG ) )
#undef CONSOLE_DMESG
#define CONSOLE_DMESG ( CONSOLE_USAGE_ALL & ~CONSOLE_USAGE_TUI )
#endif
 
/** Size of ring buffer */
#define DMESG_LEN 8192
 
/** Ring buffer */
static char dmesg[DMESG_LEN];
 
/** Offset within ring buffer */
static unsigned int dmesg_offset;
 
/** Ring buffer ANSI escape sequence handlers */
static struct ansiesc_handler dmesg_ansiesc_handlers[] = {
        { 0, NULL }
};
 
/** Ring buffer ANSI escape sequence context */
static struct ansiesc_context dmesg_ansiesc_ctx = {
        .handlers = dmesg_ansiesc_handlers,
};
 
/**
 * Print a character to the ring buffer
 *
 * @v character         Character to be printed
 */
static void dmesg_putchar ( int character ) {
 
        /* Strip ANSI escape sequences */
        character = ansiesc_process ( &dmesg_ansiesc_ctx, character );
        if ( character < 0 )
                return;
 
        /* Handle backspace characters */
        if ( character == '\b' ) {
                if ( dmesg_offset )
                        dmesg_offset--;
                return;
        }
 
        /* Record character */
        dmesg[ dmesg_offset++ % DMESG_LEN ] = character;
}
 
/** Ring buffer console driver */
struct console_driver dmesg_console __console_driver = {
        .putchar = dmesg_putchar,
        .usage = CONSOLE_DMESG,
};
 
/**
 * Fetch ring buffer setting
 *
 * @v data              Buffer to fill with setting data
 * @v len               Length of buffer
 * @ret len             Length of setting data, or negative error
 */
static int dmesg_fetch ( void *data, size_t len ) {
        uint8_t *bytes = data;
        size_t max;
        unsigned int offset;
 
        /* Calculate length */
        max = dmesg_offset;
        if ( max > DMESG_LEN )
                max = DMESG_LEN;
        if ( len > max )
                len = max;
 
        /* Copy data */
        offset = ( dmesg_offset - len );
        while ( len-- )
                *(bytes++) = dmesg[ offset++ % DMESG_LEN ];
 
        return max;
}
 
/**
 * Store ring buffer setting
 *
 * @v data              Setting data, or NULL to clear setting
 * @v len               Length of setting data
 * @ret rc              Return status code
 */
static int dmesg_store ( const void *data __unused, size_t len ) {
 
        /* Only clearing the log is supported */
        if ( len )
                return -ENOTSUP;
 
        /* Clear log */
        dmesg_offset = 0;
 
        return 0;
}
 
/** Ring buffer setting */
const struct setting dmesg_setting __setting ( SETTING_MISC, dmesg ) = {
        .name = "dmesg",
        .description = "Ring buffer",
        .type = &setting_type_string,
        .scope = &builtin_scope,
};
 
/** Ring buffer built-in setting */
struct builtin_setting dmesg_builtin_setting __builtin_setting = {
        .setting = &dmesg_setting,
        .fetch = dmesg_fetch,
        .store = dmesg_store,
};