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-$Id: README,v 1.2 2001/06/21 23:07:06 dwmw2 Exp $
-$Log: README,v $
-Revision 1.2 2001/06/21 23:07:06 dwmw2
-Initial import to MTD CVS
-
-Revision 1.1 2001/06/11 19:34:40 vipin
-Added README file to dir.
-
-
-This is the README file for the "checkfs" power fail test program.
-By: Vipin Malik
-
-NOTE: This program requires an external "power cycling box"
-connected to one of the com ports of the system under test.
-This power cycling box should wait for a random amount of time
-after it receives a "ok to power me down" message over the
-serial port, and then yank power to the system under test.
-(The box that I rigged up tested with waits anywhere from
-0 to ~40 seconds).
-
-
-It should then restore power after a few seconds and wait for the
-message again.
-
-
-ABOUT:
-
-This program's primary purpose it to test the reliiability
-of various file systems under Linux.
-
-SETUP:
-
-You need to setup the file system you want to test and run the
-"makefiles" program ONCE. This creates a set of files that are
-required by the "checkfs" program.
-
-Also copy the "checkfs" executable program to the same dir.
-
-Then you need to make sure that the program "checkfs" is called
-automatically on startup. You can customise the operation of
-the "checkfs" program by passing it various cmd line arguments.
-run "checkfs -?" for more details.
-
-****NOTE*******
-Make sure that you call the checkfs program only after you have
-mounted the file system you want to test (this is obvious), but
-also after you have run any "scan" utilities to check for and
-fix any file systems errors. The e2fsck is one utility for the
-ext2 file system. For an automated setup you of course need to
-provide these scan programs to run in standalone mode (-f -y
-flags for e2fsck for example).
-
-File systems like JFFS and JFFS2 do not have any such external
-utilities and you may call "checkfs" right after you have mounted
-the respective file system under test.
-
-There are two ways you can mount the file system under test:
-
-1. Mount your root fs on a "standard" fs like ext2 and then
-mount the file system under test (which may be ext2 on another
-partition or device) and then run "checkfs" on this mounted
-partition OR
-
-2. Make your fs AND device that you have put this fs as your
-root fs and run "checkfs" on the root device (i.e. "/").
-You can of course still run checkfs under a separate dir
-under your "/" root dir.
-
-I have found the second method to be a particularly stringent
-arrangement (and thus preferred when you are trying to break
-something).
-
-Using this arrangement I was able to find that JFFS clobbered
-some "sister" files on the root fs even though "checkfs" would
-run fine through all its own check files.
-
-(I found this out when one of the clobbered sister file happened
-to be /bin/bash. The system refused to run rc.local thus
-preventing my "checkfs" program from being launched :)
-
-"checkfs":
-
-The "formatting" reliability of the fs as well as the file data integrity
-of files on the fs can be checked using this program.
-
-"formatiing" reliability can only be checked via an indirect method.
-If there is severe formatting reliability issues with the file system,
-it will most likely cause other system failures that will prevent this
-program from running successfully on a power up. This will prevent
-a "ok to power me down" message from going out to the power cycling
-black box and prevent power being turned off again.
-
-File data reliability is checked more directly. A fixed number of
-files are created in the current dir (using the program "makefiles").
-
-Each file has a random number of bytes in it (set by using the
--s cmd line flag). The number of "ints" in the file is stored as the
-first "int" in it (note: 0 length files are not allowed). Each file
-is then filled with random data and a 16 bit CRC appended at the end.
-
-When "checkfs" is run, it runs through all files (with predetermined
-file names)- one at a time- and checks for the number of "int's"
-in it as well as the ending CRC.
-
-The program exits if the numbers of files that are corrupt are greater
-that a user specified parameter (set by using the -e cmd line flag).
-
-If the number of corrupt files is less than this parameter, the corrupt
-files are repaired and operation resumes as explained below.
-
-The idea behind allowing a user specified amount of corrupt files is as
-follows:
-
-If you are testing for "formatting" reliability of a fs, and for
-the data reliability of "other" files present of the fs, use -e 1.
-"other" files are defined as sister files on the fs, not being written to
-by the "checkfs" test program.
-
-As mentioned, in this case you would set -e 1, or allow at most 1 file
-to be corrupt each time after a power fail. This would be the file
-that was probably being written to when power failed (and CRC was not
-updated to reflect the new data being written). You would check file
-systems like ext2 etc. with such a configuration.
-(As you have no hope that these file systems provide for either your
-new data or old data to be present in the file if power failed during
-the write. This is called "roll back and recover".)
-
-With JFFS2 I tested for such "roll back and recover" file data reliability
-by setting -e 0 and making sure that all writes to the file being
-updated are done in a *single* write().
-
-This is how I found that JFFS2 (yet) does NOT support this functionality.
-(There was a great debate if this was a bug or a feature that was lacking
-or even an issue at all. See the mtd archives for more details).
-
-In other words, JFFS2 will partially update a file on FLASH even before
-the write() command has completed, thus leaving part old data part new
-data in your file if power failed in the middle of a write().
-
-This is bad functionality if you are updating a binary structure or a
-CRC protected file (as in our case).
-
-
-If All Files Check Out OK:
-
-On the startup scan, if there are less errors than specified by the "-e flag"
-a "ok to power me down message" is sent via the specified com port.
-
-The actual format of this message will depend on the format expected
-by the power cycling box that will receive this message. One may customise
-the actual message that goes out in the "do_pwr_dn)" routine in "comm.c".
-
-This file is called with an open file descriptor to the comm port that
-this message needs to go out over and the count of the current power
-cycle (in case your power cycling box can display/log this count).
-
-After this message has been sent out, the checkfs program goes into
-a while(1) loop of writing new data (with CRC), one at a time, into
-all the "check files" in the dir.
-
-Its life comes to a sudden end when power is asynchronously pulled from
-under its feet (by your external power cycling box).
-
-It comes back to life when power is restored and the system boots and
-checkfs is called from the rc.local script file.
-
-The cycle then repeats till a problem is detected, at which point
-the "ok to power me down" message is not sent and the cycle stops
-waiting for the user to examine the system.
-
-
-
-