UBI: recover_peb and power cut safety

["Jörg Pfähler" <pfaehler@isse.de>]

Hi,

I would greatly appreciate some clarification with respect to power cut safety 
during writing of an erase block in UBI, specifically power cut safety of 
recover_peb.

During a normal write operation (ubi_eba_write_leb in mtd/ubi/eba.c) UBI tries 
to move the contents of the block (and the new contents) to a new location via 
recover_peb, if the write fails. However, recover_peb does not seem to use the 
capability to exchange the (logical) block atomically (as 
ubi_eba_atomic_leb_change in mtd/ubi/eba.c does). Specifically, it does not 
seem to write the amount of data and its checksum to the VID header. Thus, if 
the system crashes in the middle of recover_peb before the old/broken block 
could be erased, we are left with a newer version of the block (the sequence 
number in the header is increased by recover_peb), but without having moved 
all the contents of the old block. This would obviously lead to data loss. 
Thus, It seems to me that recover_peb (and therefore ubi_eba_write_leb) is not 
power cut safe or is there some other mechanism distinct from the one used by 
ubi_eba_atomic_leb_change to achieve this? If not I would suggest using 
ubi_eba_atomic_leb_change in ubi_eba_write_leb instead of recover_peb.

Thanks in advance for any clarifications!
Regards,
Jörg

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Jörg Pfähler
Lehrstuhl für Softwaretechnik
Institut für Software and Systems Engineering
Universität Augsburg

Universitätsstr. 6a, Raum 3014
tel:      (+49) 821/598-2229
e-mail:   joerg.pfaehler@informatik.uni-
augsburg.de<mailto:joerg.pfaehler@informatik.uni-augsburg.de>
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