[PATCH] UBI: optimize vid-header IO read checks

[Gupta, Pekon]

> On Thu, 2013-05-16 at 06:38 +0000, Gupta, Pekon wrote:
> > Hi,
> >
> > Requesting feedbacks/comments on this one too ?
> > This should be independent of previous one..
> 
> How did you test this change? Did you test that we do not die in
> scanning in case of bit-flips? How about ECC errors? Do we scrub
> eraseblocks then?
> 
Hi,

Attaching the logs for tests I ran to for ec_hdr patch. Added 
following printk to cross-check the result.
- printk in scan_peb() to check return values of ubi_io_read_ec_hdr()  
- printk in scan_peb() to check return values of ubi_io_read_vid_hdr()
- printk in do_sync_erase() to check if bit-flipped PEB is scrubbed

s/*UBI in attached logs..


Test 1: introduced correctable bit-flips in ec_header of PEB=1
- Observations:
- UBI: fixable bit-flip detected at PEB 1
	*UBI:ubi_io_read_ec_hdr: PEB=1, OK
	*UBI:scan_peb: PEB=1: ec_hdr=UBI_IO_BITFLIPS
	*UBI:scan_peb: PEB=1: ec_hdr acceptable
	*UBI:scan_peb: PEB=1: vid_hdr=UBI_IO_FF
- PEB 1 scubbed
	*UBI:do_sync_erase: PEB=1 erasing ..
	*UBI:ubi_io_sync_erase: PEB=1: erase successful> --
- UBIFS: mounted UBI device 0, volume 0, name "test"



Test 2: introduced un-correctable bit-flips in ec_header of PEB=1
-Observations:
- warning: ubi_io_read: error -74 (ECC error) while reading 64 bytes from PEB 1:0
	<stack_dump>
	*UBI:ubi_io_read_ec_hdr: PEB=1, EBADMSG
	*UBI:scan_peb: PEB=1: ec_hdr=UBI_IO_BAD_HDR_EBADMSG
- vid_hdr not parsed due to reasons below (un-correctable bit-flips)
	+	/* un=recoverable erase-header
	+	* unknown erase-count: can be set to mean erase-count.
	+	* unknown image_seq: cannot determine if PEB was programmed
	+	* unknown version: cannot determine UBI protocol to use
	+	* So no point in checking vid_hdr, schedule this PEB for erase. */
- PEB 1 scrubbed
	*UBI:do_sync_erase: PEB=1 erasing ..
	*UBI:ubi_io_sync_erase: PEB=1: erase successful
- UBIFS: mounted UBI device 0, volume 0, name "test"



Test 3: Normal case without any bit-flip
- Observations
- Both ec_hdr and vid_hdr scanned ok
	*UBI:scan_peb: PEB=1: ec_hdr=OK
	*UBI:scan_peb: PEB=1: ec_hdr acceptable
	*UBI:scan_peb: PEB=1: vid_hdr=UBI_IO_FF
- no scrubbing required, volume mounted.
- UBIFS: mounted UBI device 0, volume 0, name "test"



Hope that helps in understanding the attached logs..
(1) Request you to review the tables in patch description, in case I missed 
any corner case. 
(2) Also if you would like me to check any scenario explicitly.
(3) I have similar results for vid_hdr patch, I'll share it separately.


with regards, pekon
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