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mtd: Introduce an expert mode for forensics and debugging purposes

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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: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20211118114659.1282855-1-miquel.raynal@bootlin.com
This commit is contained in:
Miquel Raynal 2021-11-18 12:46:59 +01:00
parent 00596576a0
commit 67b967ddd9
5 changed files with 22 additions and 0 deletions
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10
drivers/mtd/mtdcore.c
View file

@ -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;

3
drivers/mtd/nand/core.c
View file

@ -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;

3
drivers/mtd/nand/raw/nand_base.c
View file

@ -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);

3
drivers/mtd/nand/raw/nand_bbt.c
View file

@ -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;

3
include/linux/mtd/mtd.h
View file

@ -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__ */