[Baypiggies] File IO question

Ken Seehart ken at seehart.com
Tue Jul 25 14:09:50 CEST 2006

I am writing a linux embedded application that writes to a FLASH disk.  
It needs to reliably recover from a power down at any time.  So I have 
implemented a tandem file writing scheme to ensure that an uncorrupted 
version of the data file exists.  I am using shelve for my pair of 
tandem data files because it is sufficient for my needs.  I use a pair 
of single byte binary files to record the status of the data files.

My question is this: If I write a single byte to a file that contains 
exactly one byte, can I be sure that a power outage during the write 
will not render the file unreadable?

f = open("valid", "w")
f = open("valid", "w")

In other words, if the file initially contains a 0 or 1, and the above 
code is executed repeatedly, can I be sure that my file will contain a 0 
or 1 if the power is shut off at a random time during execution?

- Ken

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