RFC : attach ubi in readonly mode

PATCH Matthieu CASTET 3 participants 3 messages Feb 3, 2012 – Oct 4, 2012

Subsystems (2)

Memory technology devices (MTD) Unsorted block images (UBI)

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Matthieu CASTET

author

2012-02-03 13:40 UTC #0 lore raw

Hi,

it could be interesting to attach ubi in read-only mode (for example getting ubi volume info without altering flash).

A solution to do that could be to add an argument to UBI_IOCATT ioctl.

Another solution should be to have a way to switch MTD_WRITEABLE flags.

What do you think a that ?

PS : attached a proof of concept for solution 1

drivers/mtd/ubi/build.c +9 -2

index 13b05cb..56c2249 100644
@@ -841,6 +841,7 @@ static int autoresize(struct ubi_device *ubi, int vol_id)
  * @mtd: MTD device description object
  * @ubi_num: number to assign to the new UBI device
  * @vid_hdr_offset: VID header offset
+ * @ro : attach in readonly mode
  *
  * This function attaches MTD device @mtd_dev to UBI and assign @ubi_num number
  * to the newly created UBI device, unless @ubi_num is %UBI_DEV_NUM_AUTO, in

@@ -851,7 +852,7 @@ static int autoresize(struct ubi_device *ubi, int vol_id)
  * Note, the invocations of this function has to be serialized by the
  * @ubi_devices_mutex.
  */
-int ubi_attach_mtd_dev(struct mtd_info *mtd, int ubi_num, int vid_hdr_offset)
+int ubi_attach_mtd_dev(struct mtd_info *mtd, int ubi_num, int vid_hdr_offset, int ro)
 {
 	struct ubi_device *ubi;
 	int i, err, ref = 0;

@@ -922,6 +923,12 @@ int ubi_attach_mtd_dev(struct mtd_info *mtd, int ubi_num, int vid_hdr_offset)
 
 	ubi_msg("attaching mtd%d to ubi%d", mtd->index, ubi_num);
 
+	if (ro) {
+		ubi_msg("attach in "
+			"read-only mode");
+		ubi->ro_mode = 1;
+	}
+
 	err = io_init(ubi);
 	if (err)
 		goto out_free;

@@ -1209,7 +1216,7 @@ static int __init ubi_init(void)
 
 		mutex_lock(&ubi_devices_mutex);
 		err = ubi_attach_mtd_dev(mtd, UBI_DEV_NUM_AUTO,
-					 p->vid_hdr_offs);
+					 p->vid_hdr_offs, 0);
 		mutex_unlock(&ubi_devices_mutex);
 		if (err < 0) {
 			ubi_err("cannot attach mtd%d", mtd->index);

drivers/mtd/ubi/cdev.c +1 -1

index 4dfa6b9..9be009f 100644
@@ -1007,7 +1007,7 @@ static long ctrl_cdev_ioctl(struct file *file, unsigned int cmd,
 		 * 'ubi_attach_mtd_dev()'.
 		 */
 		mutex_lock(&ubi_devices_mutex);
-		err = ubi_attach_mtd_dev(mtd, req.ubi_num, req.vid_hdr_offset);
+		err = ubi_attach_mtd_dev(mtd, req.ubi_num, req.vid_hdr_offset, req.padding[0]);
 		mutex_unlock(&ubi_devices_mutex);
 		if (err < 0)
 			put_mtd_device(mtd);

drivers/mtd/ubi/ubi.h +1 -1

index a637f02..aff929f 100644
@@ -550,7 +550,7 @@ int ubi_io_write_vid_hdr(struct ubi_device *ubi, int pnum,
 			 struct ubi_vid_hdr *vid_hdr);
 
 /* build.c */
-int ubi_attach_mtd_dev(struct mtd_info *mtd, int ubi_num, int vid_hdr_offset);
+int ubi_attach_mtd_dev(struct mtd_info *mtd, int ubi_num, int vid_hdr_offset, int ro);
 int ubi_detach_mtd_dev(int ubi_num, int anyway);
 struct ubi_device *ubi_get_device(int ubi_num);
 void ubi_put_device(struct ubi_device *ubi);

Artem Bityutskiy

2012-02-03 14:07 UTC #1 lore raw

Quoted 6 lines · Matthieu CASTET

Hi,
it could be interesting to attach ubi in read-only mode (for example getting ubi volume info without altering flash).
A solution to do that could be to add an argument to UBI_IOCATT ioctl.

No objections in general, especially if you also:

1. amend the mtd-utils and add support for this option
2. add a piece of doc for the mtd web site
3. add a test for this feature to mtd-utils.git/tests/ubi-test/ (probably simpler to improve one of the existing tests there)

Quoted 1 line

Another solution should be to have a way to switch MTD_WRITEABLE flags.

This can be done as well, up to you. But I guess UBI will need changes anyway to handle gracefully situation like:

1. you have RW partition, do a lot of I/O, then reboot uncleanly, so that there are many erase operations unfinished

2. You reboot, mark the partition R/O, try to attach it - UBI will probably anyway try to erase some blocks and get -EFORS, not sure will it panic or not. Should be tested, but probably not a big deal.

IOW, both approaches should be OK.

Signature · 2 lines

Best Regards,
Artem Bityutskiy

Marek Vasut

2012-10-04 00:19 UTC #2 lore raw

In reply to Matthieu CASTET

Dear Matthieu CASTET,

Quoted 5 lines

Hi,
it could be interesting to attach ubi in read-only mode (for example getting ubi volume info without altering flash).

Quoted 8 lines

A solution to do that could be to add an argument to UBI_IOCATT ioctl.
Another solution should be to have a way to switch MTD_WRITEABLE flags.
What do you think a that ?
PS : attached a proof of concept for solution 1

Did you get any further with this patches? Is it now possible to safely mount UBIFS in read-only mode in some way please?

Thanks!

Best regards,
Marek Vasut