Commit 67b967dd authored by Miquel Raynal's avatar Miquel Raynal
Browse files

mtd: Introduce an expert mode for forensics and debugging purposes 



When developping NAND controller drivers or when debugging filesystem
corruptions, it is quite common to need hacking locally into the
MTD/NAND core in order to get access to the content of the bad
blocks. Instead of having multiple implementations out there let's
provide a simple yet effective specific MTD-wide debugfs entry to fully
disable these checks on purpose.

A warning is added to inform the user when this mode gets enabled.

Signed-off-by: default avatarMiquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20211118114659.1282855-1-miquel.raynal@bootlin.com
parent 00596576

drivers/mtd/mtdcore.c

+10 −0
Original line number Diff line number Diff line
@@ -2370,6 +2370,14 @@ static struct backing_dev_info * __init mtd_bdi_init(const char *name) 
	return ret ? ERR_PTR(ret) : bdi;

}



char *mtd_expert_analysis_warning =

	"Bad block checks have been entirely disabled.\n"

	"This is only reserved for post-mortem forensics and debug purposes.\n"

	"Never enable this mode if you do not know what you are doing!\n";

EXPORT_SYMBOL_GPL(mtd_expert_analysis_warning);

bool mtd_expert_analysis_mode;

EXPORT_SYMBOL_GPL(mtd_expert_analysis_mode);



static struct proc_dir_entry *proc_mtd;



static int __init init_mtd(void)
@@ -2393,6 +2401,8 @@ static int __init init_mtd(void) 
		goto out_procfs;



	dfs_dir_mtd = debugfs_create_dir("mtd", NULL);

	debugfs_create_bool("expert_analysis_mode", 0600, dfs_dir_mtd,

			    &mtd_expert_analysis_mode);



	return 0;

drivers/mtd/nand/core.c

+3 −0
Original line number Diff line number Diff line
@@ -21,6 +21,9 @@ 
 */

bool nanddev_isbad(struct nand_device *nand, const struct nand_pos *pos)

{

	if (WARN_ONCE(mtd_expert_analysis_mode, mtd_expert_analysis_warning))

		return false;



	if (nanddev_bbt_is_initialized(nand)) {

		unsigned int entry;

		int status;

drivers/mtd/nand/raw/nand_base.c

+3 −0
Original line number Diff line number Diff line
@@ -321,6 +321,9 @@ static int nand_isbad_bbm(struct nand_chip *chip, loff_t ofs) 
	if (nand_region_is_secured(chip, ofs, mtd->erasesize))

		return -EIO;



	if (WARN_ONCE(mtd_expert_analysis_mode, mtd_expert_analysis_warning))

		return 0;



	if (chip->legacy.block_bad)

		return chip->legacy.block_bad(chip, ofs);

drivers/mtd/nand/raw/nand_bbt.c

+3 −0
Original line number Diff line number Diff line
@@ -1455,6 +1455,9 @@ int nand_isbad_bbt(struct nand_chip *this, loff_t offs, int allowbbt) 
	pr_debug("nand_isbad_bbt(): bbt info for offs 0x%08x: (block %d) 0x%02x\n",

		 (unsigned int)offs, block, res);



	if (WARN_ONCE(mtd_expert_analysis_mode, mtd_expert_analysis_warning))

		return 0;



	switch (res) {

	case BBT_BLOCK_GOOD:

		return 0;

include/linux/mtd/mtd.h

+3 −0
Original line number Diff line number Diff line
@@ -711,4 +711,7 @@ static inline int mtd_is_bitflip_or_eccerr(int err) { 


unsigned mtd_mmap_capabilities(struct mtd_info *mtd);



extern char *mtd_expert_analysis_warning;

extern bool mtd_expert_analysis_mode;



#endif /* __MTD_MTD_H__ */