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Commit 9a78bc83 authored by Christian Riesch's avatar Christian Riesch Committed by Brian Norris
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mtd: Fix the behavior of OTP write if there is not enough room for data 

If a write to one time programmable memory (OTP) hits the end of this
memory area, no more data can be written. The count variable in
mtdchar_write() in drivers/mtd/mtdchar.c is not decreased anymore.
We are trapped in the loop forever, mtdchar_write() will never return
in this case.

The desired behavior of a write in such a case is described in [1]:
- Try to write as much data as possible, truncate the write to fit into
  the available memory and return the number of bytes that actually
  have been written.
- If no data could be written at all, return -ENOSPC.

This patch fixes the behavior of OTP write if there is not enough space
for all data:

1) mtd_write_user_prot_reg() in drivers/mtd/mtdcore.c is modified to
   return -ENOSPC if no data could be written at all.
2) mtdchar_write() is modified to handle -ENOSPC correctly. Exit if a
   write returned -ENOSPC and yield the correct return value, either
   then number of bytes that could be written, or -ENOSPC, if no data
   could be written at all.

Furthermore the patch harmonizes the behavior of the OTP memory write
in drivers/mtd/devices/mtd_dataflash.c with the other implementations
and the requirements from [1]. Instead of returning -EINVAL if the data
does not fit into the OTP memory, we try to write as much data as
possible/truncate the write.

[1] http://pubs.opengroup.org/onlinepubs/9699919799/functions/write.html



Signed-off-by: default avatarChristian Riesch <christian.riesch@omicron.at>
Signed-off-by: default avatarBrian Norris <computersforpeace@gmail.com>
parent ea6d833a

drivers/mtd/devices/mtd_dataflash.c

+10 −6
Original line number Diff line number Diff line
@@ -542,14 +542,18 @@ static int dataflash_write_user_otp(struct mtd_info *mtd, 
	struct dataflash	*priv = mtd->priv;

	int			status;



	if (len > 64)

		return -EINVAL;



	/* Strictly speaking, we *could* truncate the write ... but

	 * let's not do that for the only write that's ever possible.

	if (from >= 64) {

		/*

		 * Attempting to write beyond the end of OTP memory,

		 * no data can be written.

		 */

		*retlen = 0;

		return 0;

	}



	/* Truncate the write to fit into OTP memory. */

	if ((from + len) > 64)

		return -EINVAL;

		len = 64 - from;



	/* OUT: OP_WRITE_SECURITY, 3 zeroes, 64 data-or-zero bytes

	 * IN:  ignore all

drivers/mtd/mtdchar.c

+9 −0
Original line number Diff line number Diff line
@@ -324,6 +324,15 @@ static ssize_t mtdchar_write(struct file *file, const char __user *buf, size_t c 
		default:

			ret = mtd_write(mtd, *ppos, len, &retlen, kbuf);

		}



		/*

		 * Return -ENOSPC only if no data could be written at all.

		 * Otherwise just return the number of bytes that actually

		 * have been written.

		 */

		if ((ret == -ENOSPC) && (total_retlen))

			break;



		if (!ret) {

			*ppos += retlen;

			total_retlen += retlen;

drivers/mtd/mtdcore.c

+11 −1
Original line number Diff line number Diff line
@@ -932,12 +932,22 @@ EXPORT_SYMBOL_GPL(mtd_read_user_prot_reg); 
int mtd_write_user_prot_reg(struct mtd_info *mtd, loff_t to, size_t len,

			    size_t *retlen, u_char *buf)

{

	int ret;



	*retlen = 0;

	if (!mtd->_write_user_prot_reg)

		return -EOPNOTSUPP;

	if (!len)

		return 0;

	return mtd->_write_user_prot_reg(mtd, to, len, retlen, buf);

	ret = mtd->_write_user_prot_reg(mtd, to, len, retlen, buf);

	if (ret)

		return ret;



	/*

	 * If no data could be written at all, we are out of memory and

	 * must return -ENOSPC.

	 */

	return (*retlen) ? 0 : -ENOSPC;

}

EXPORT_SYMBOL_GPL(mtd_write_user_prot_reg);