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mtd-rw.c
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mtd-rw.c
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/*
* mtd-rw - Make all MTD partitions writeable.
*
* Copyright (C) 2016 Joseph C. Lehner <joseph.c.lehner@gmail.com>
*
* 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; version 2 of the License.
*
* 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, see <http://www.gnu.org/licenses/>.
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/mtd/mtd.h>
#include <linux/err.h>
/*
* This module is intended for embedded devices where the mtd partition
* layout may be hard-coded in the firmware. If, for some reason, you
* DO have to write to a read-only partition (which is often a bad idea),
* this module is the way to go.
*
* The module is currently limited to the first 64 partitions, but this
* should suffice for most purposes.
*
* Inspired by dougg3@electronics.stackexchange.com:
* https://electronics.stackexchange.com/a/116133/97342
*/
#ifndef MODULE
#error "Must be compiled as a module."
#endif
#define MOD_WARNING KERN_WARNING "mtd-rw: "
#define MOD_INFO KERN_INFO "mtd-rw: "
#define MOD_ERR KERN_ERR "mtd-rw: "
#define MTD_MAX (8 * sizeof(unlocked))
static uint64_t unlocked = 0;
static unsigned mtd_last = 0;
static bool i_want_a_brick = false;
module_param(i_want_a_brick, bool, S_IRUGO);
MODULE_PARM_DESC(i_want_a_brick, "Make all partitions writeable");
static int set_writeable(unsigned n, bool w)
{
struct mtd_info *mtd = get_mtd_device(NULL, n);
int err;
if (IS_ERR(mtd)) {
if (PTR_ERR(mtd) != -ENODEV || !w) {
printk(MOD_ERR "mtd%d: error %ld\n", n, PTR_ERR(mtd));
}
return PTR_ERR(mtd);
}
err = -EEXIST;
if (w && !(mtd->flags & MTD_WRITEABLE)) {
printk(MOD_INFO "mtd%d: setting writeable flag\n", n);
mtd->flags |= MTD_WRITEABLE;
err = 0;
} else if (!w && (mtd->flags & MTD_WRITEABLE)) {
printk(MOD_INFO "mtd%d: clearing writeable flag\n", n);
mtd->flags &= ~MTD_WRITEABLE;
err = 0;
}
put_mtd_device(mtd);
return err;
}
static int __init mtd_rw_init(void)
{
int i, err;
if (!i_want_a_brick) {
printk(MOD_ERR "must specify i_want_a_brick=1 to continue\n");
return -EINVAL;
}
for (i = 0; i < MTD_MAX; ++i) {
err = set_writeable(i, true);
if (!err) {
unlocked |= (1 << i);
} else if (err == -ENODEV) {
break;
}
}
if (i == MTD_MAX) {
printk(MOD_WARNING "partitions beyond mtd%d are ignored\n", i - 1);
}
if (!unlocked) {
printk(MOD_INFO "no partitions to unlock\n");
return -ENODEV;
}
mtd_last = i;
return 0;
}
static void __exit mtd_rw_exit(void)
{
unsigned i;
for (i = 0; i < mtd_last; ++i) {
if (unlocked & (1 << i)) {
set_writeable(i, false);
}
}
}
module_init(mtd_rw_init);
module_exit(mtd_rw_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Joseph C. Lehner <joseph.c.lehner@gmail.com>");
MODULE_DESCRIPTION("Write-enabler for MTD partitions");
MODULE_VERSION("1");