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annotate mpffs/Description @ 27:343b6b2f178b

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beginning of Mokopir-FFS verbal description
author Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
date Sun, 30 Jun 2013 01:17:30 +0000
parents
children c9f7a4afccc9
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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27
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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1 This is a description, based on reverse engineering, of the flash file system
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
2 (FFS) implemented in Pirelli's original firmware for the DP-L10 GSM/WiFi dual
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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3 mode mobile phone, and in the Closedmoko GTA0x modem firmware. Not knowing the
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
4 "proper" name for this FFS, and needing _some_ identifier to refer to it, I
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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5 have named it Mokopir-FFS, from "Moko" and "Pirelli" - sometimes abbreviated
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
6 further to MPFFS.
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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7
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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8 (I have previously called the FFS in question MysteryFFS; but now that I've
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
9 successfully reverse-engineered it, it isn't such a mystery any more :-)
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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10
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
11 At a high functional level, Mokopir-FFS presents the following features:
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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12
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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13 * Has a directory tree structure like UNIX file systems;
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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14
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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15 * The file system API that must be implemented inside the proprietary firmware
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
16 appears to use UNIX-style pathnames; doing strings on firmware images reveals
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
17 pathname strings like these:
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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18
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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19 /var/dbg/dar
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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20 /gsm/l3/rr_white_list
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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21 /gsm/l3/rr_medium_rxlev_thr
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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22 /gsm/l3/rr_upper_rxlev_thr
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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23 /gsm/l3/shield
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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24
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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25 Parsing the corresponding FFS image with tools included in the present
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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26 package has confirmed that the directory structure implied by these pathnames
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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27 does indeed exist in the FFS.
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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28
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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29 * Absolutely no DOS-ish semantics seen anywhere: no 8.3 filenames and no
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
30 colon-separated device names (seen in the TSM30 file system source, for
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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31 example) are visible in the Closedmoko/Pirelli FFS.
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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32
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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33 * File contents are stored uncompressed, but not necessarily contiguous: one
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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34 could probably store a file in FFS which is bigger than the flash sector
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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35 size, it which case it can never be contiguous in a writable FFS (see below),
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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36 and the firmware implementation seems to limit chunk sizes to a fairly small
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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37 number: on the Pirelli phones all largish files are divided into chunks of
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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38 8 KiB each, and on my GTA02 the largest observed chunk size is only 2 KiB.
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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39
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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40 The smaller files, like the IMEI and the firmware ID strings in my GTA02 FFS,
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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41 are contiguous.
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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42
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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43 * The FFS structure is such that the length of "user" payload data stored in
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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44 each chunk (and consequently, in each file) can be known exactly in bytes,
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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45 with the files/chunks able to contain arbitrary binary data. (This property
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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46 may seem obvious or trivial, as all familiar UNIX and DOS file systems have
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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47 it, but contrast with RT-11 for example.)
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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48
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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49 * The flash file system is a writable one: the running firmware can create,
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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50 delete and overwrite files (and possibly directories too) in the live FFS;
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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51 thus the FFS design is such that allows these operations to be performed
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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52 within the physical constraints of NOR flash write operations.
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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53
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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54 I have reverse-engineered this Mokopir-FFS on a read-only level. What it means
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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55 is that I, or anyone else who can read this document and the accompanying
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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56 source for the listing/extraction utilities, can take a Mokopir-FFS image read
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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57 out of a device and see/extract its full content: the complete directory tree
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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58 and the exact binary byte content of all files contained therein.
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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59
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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60 However, the knowledge possessed by the present hacker (and conveyed in this
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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61 document and the accompanying source code) is NOT sufficient for constructing a
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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62 valid Mokopir-FFS image "in vitro" given a tree of directories and files, or
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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63 for making modifications to the file or directory content on an existing image
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
64 and producing a content-modified image that is also valid; valid as in suitable
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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65 for the original proprietary firmware to make its normal read and write
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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66 operations without noticing anything amiss.
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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67
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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68 Constructing "de novo" Mokopir-FFS images or modifying existing images in such
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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69 a way that they remain 100% valid for all read and write operations of the
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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70 original proprietary firmware would, at the very minimum, require an
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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71 understanding of the meaning of *all* fields on the on-media FFS format. Some
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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72 of these fields are still left as "non-understood" for now though: a read-only
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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73 implementation can get away with simply ignoring them, but a writer/generator
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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74 would have to put *something* in those fields.
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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75
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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76 As you read the "read-only" description of the Mokopir-FFS on-media format in
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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77 the remainder of this document, it should become fairly obvious which pieces
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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78 are missing before our understanding of this FFS can be elevated to a
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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79 "writable" level.
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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80
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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81 However, when it comes to writing new code to run on the two Calypso phones in
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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82 question (Closedmoko and Pirelli), it seems, at least to the present hacker,
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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83 that a read-only understanding of Mokopir-FFS should be sufficient:
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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84
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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85 * In the case of Closedmoko GTA0x modems, the FFS is seen to contain the IMEI
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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86 and the RF calibration data. The format of the former is obvious; the latter
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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87 not so much - but in any case, the information of interest is clearly of a
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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88 read-only nature. It's difficult to tell (or rather, I haven't bothered to
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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89 experiment enough) whether the Closedmoko firmware does any writes to FFS or
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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90 if the FFS is treated as read-only outside of the production line environment,
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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91 but in any case, it seems to me that for any 3rd party replacement firmware,
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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92 the best strategy would be to treat the FFS as a read-only source of IMEI and
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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93 RF calibration data, and nothing more.
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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94
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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95 * In the case of Pirelli phones, the FFS is used to store user data: sent and
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
96 received SMS (and MMS/email/whatever), call history, UI settings, pictures
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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97 taken with the camera, and whatever else. It also stores a ton of files
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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98 which I can only presume were meant to be immutable except at the time of
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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99 firmware updates: graphics for the UI, ringtones, i18n UI strings, and even
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
100 "helper" firmware images for the WiFi and VoIP processors. However, no IMEI
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
101 or RF calibration data are anywhere to be found in the FFS - instead this
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
102 information appears to be stored in the "factory block" at the end of the
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
103 flash (in its own sector) outside of the FFS.
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
104
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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105 Being able to parse FFS images extracted out of Pirelli phones "in vitro"
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
106 allows us to steal some of these helper files (UI artwork, ringtones,
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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107 WiFi/VoIP helpers), and some of these might even come useful to firmware
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
108 replacement projects, but it seems to me that a replacement firmware would
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
109 be better off using its own FFS design for storing user data, and as to
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
110 retrieving the original IMEI and RF calibration data, the original FFS isn't
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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111 of any use for that anyway.
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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112
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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113 =======================
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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114 Moko/Pirelli FFS format
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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115 =======================
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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116
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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117 OK, now that I'm done with the introduction, we can get to the actual
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
118 Mokopir-FFS format.
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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119
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Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
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120 * On the GTA0x modem (or at least on my GTA02; my sample size is 1) the FFS
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
121 occupies 7 flash sectors of 64 KiB each at offsets 0x380000 through 0x3E0000,
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
122 inclusive.
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
123
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
124 (The 4 MiB NOR flash chip used by Closedmoko has an independent R/W bank
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
125 division between the first 3 MiB and the last 1 MiB. The first 3 MiB are used
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
126 to hold the field-flashable closed firmware images distributed as *.m0 files;
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
127 the independent last megabyte holds the FFS, and thus the FW could be
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
128 implemented to do FFS writes while running from flash in the main bank.
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
129 Less than half of that last megabyte appears to be used for the FFS though;
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
130 the rest appears to be unused - blank flash observed.)
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
131
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
132 * On the Pirelli the FFS occupies 18 sectors of 256 KiB each at offsets 0
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
133 through 0x440000 (inclusive) of the 2nd flash chip select, the one wired to
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
134 nCS3 on the Calypso.
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
135
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
136 Each flash sector allocated to FFS begins with the following signature:
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
137
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
138 00000000: 46 66 73 23 10 02 xx yy zz FF FF FF FF FF FF FF Ffs#............
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
139
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
140 The bytes shown as xx and yy above serve a non-understood purpose; as a guess,
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
141 they may hold some info for the flash wear leveling algorithm: in a "virgin"
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
142 FFS image like that found in my GTA02 (which never had a SIM card in it and
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
143 never made or received a call) or read out of a "virgin" Pirelli phone that
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
144 hasn't seen any active use yet, both of these bytes are FFs, but when I look at
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
145 FFS images read out of the Pirelli which I currently use as my everyday-use
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
146 cellphone, I see other values in sectors which must have been erased and
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
147 rewritten. A read-only implementation can ignore these bytes, as mine does.
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
148
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
149 The byte shown as zz is more important though, even to a read-only
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
150 implementation. The 3 values I've encountered in this byte so far are AB, BD
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
151 and BF. Per my current understanding, in a "healthy" FFS exactly one sector
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
152 will have AB in its header, exactly one will have BF, and the rest will have
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
153 BD. The meanings are (or appear to be):
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
154
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
155 AB: the sector holds a vital data structure which I have called the active
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
156 index block;
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
157 BD: the sector holds regular data;
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
158 BF: the sector is blank except for the header, can be turned into a new AB or
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
159 BD.
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
160
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
161 (Note that a flash program operation, which can turn 1s into 0s but not the
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
162 other way around, can turn BF into either AB or BD - but neither AB nor BD can
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
163 be turned into any other valid value.)
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
164
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
165 In a "virgin" FFS image (as explained above) the first FFS sector is AB, the
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
166 last one is BF, and the ones in between are BDs.
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
167
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
168 An FFS read operation (a search for a given pathname, or a listing of all
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
169 present directories and files) needs to start with locating the active index
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
170 block - the FFS sector with AB in the header. Following this header, which is
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
171 treated as being 16 bytes long (almost everything in Mokopir-FFS is aligned on
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
172 16-byte boundaries), the active index block contains a linear array of 16-byte
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
173 records, each record describing an FFS object: directory, file or file
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
174 continuation chunk.
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
175
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
176 Here is my current understanding of the 16-byte index block record structure:
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
177
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
178 2 bytes: Length of the described chunk in bytes
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
179 1 byte: Purpose/meaning not understood, ignored by my current code
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
180 1 byte: Object type
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
181 2 bytes: Descendant pointer
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
182 2 bytes: Sibling pointer
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
183 4 bytes: Data pointer
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
184 4 bytes: Purpose/meaning not understood, ignored by my current code
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
185
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
186 (On the Calypso phones of interest, all multibyte fields are in the native
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
187 little-endian byte order of the ARM7TDMI processor.)
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
188
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
189 The active index block gets filled with these records as objects are created;
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
190 the first record goes right after the 'Ffs#'...AB header (padded to 16 bytes);
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
191 the last record (at any given moment) is followed by blank flash for the
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
192 remainder of the sector. Records thus appear in the order in which they are
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
193 created, which bears no direct relation to the directory tree structure.
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
194
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
195 The objects, each described by a record in the index block, are organized into
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
196 a tree structure by the descendant and sibling pointers, plus the object type
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
197 indicator byte. Let's start with the latter; the following objtype byte values
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
198 have been observed:
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
199
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
200 00: deleted object - a read-only implementation should ignore everything except
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
201 the descendant and sibling pointers. (A write-capable implementation would
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
202 need more care - it would need a way of reclaiming dirty flash space taken
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
203 up by deleted/overwritten files.)
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
204
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
205 E1: a special file - see the description of the /.journal file further down
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
206 F1: a regular file (head chunk thereof)
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
207 F2: a directory
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
208 F4: file continuation chunk (explained below)
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
209
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
210 Each record in the index block has an associated chunk in one of the data
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
211 sectors; the index record contains fields giving the address and length of this
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
212 chunk. The length of a chunk is always a nonzero multiple of 16 bytes, and is
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
213 stored (as a number in bytes) in the first 16-bit field of the 16-byte index
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
214 entry. The address of each chunk is given by the data pointer field of the
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
215 index record, and it is reckoned in 16-byte units (thereby 16-byte alignment is
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
216 required) from the beginning of the FFS sector group in the flash address space.
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
217
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
218 For objects of type F1 and F2 (regular files and directories) the just-described
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
219 chunk begins with the name of the file or subdirectory as a NUL-terminated ASCII
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
220 string. This name is just for the current level of the directory tree, just
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
221 like in UNIX directories, thus one will have chunk names like gsm, l3, eplmn
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
222 etc, rather than /gsm/l3/eplmn. One practical effect is that one can't readily
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
223 see pathnames or any of the directory structure by looking at an FFS image as a
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
224 raw hex dump; the structure is only revealed when one uses a parsing program
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
225 like those which accompany this document.
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
226
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
227 In the case of directories, the "chunk" part of the object contains only the
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
228 name of the directory itself, padded with FFs to a 16-byte boundary. For
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
229 example, an FFS directory named /gsm would be represented by an object
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
230 consisting of two flash writes: a 16-byte entry in the active index block, with
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
231 the object type byte set to F2, and a corresponding 16-byte chunk in one of the
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
232 data sectors, with the 16 bytes containing "gsm", a terminating NUL byte, and
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
233 12 FF bytes to pad up to 16. In the case of files, this name may be following
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
234 by the first chunk of file data content, as explained further down.
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
235
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
236 In order to parse the FFS directory tree (whether the objective is to dump the
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
237 whole thing recursively or to find a specific file given a pathname), one needs
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
238 to first (well, after finding the active AB block) find the root directory node.
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
239 The root directory object is similar to other directory objects: it has a type
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
240 of F2, and an associated chunk of 16 bytes in one of the data sectors. The
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
241 latter contains the name of the root node: on the Pirelli it is "/", whereas on
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
242 my GTA02 it is "/ffs-root".
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
243
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
244 The astute reader should notice that it really makes no sense to store a name
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
245 for the root node, and indeed, this name plays no part in the traversal of the
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
246 directory tree given an absolute pathname. But instead this name, or rather
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
247 its first character, appears to be used for the purpose of locating the root
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
248 node itself. At first I had assumed that the index record for the root node is
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
249 always the first record in the active index block right after the signature
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
250 header - that is how it is in "virgin" FFS images, and also in some quite non-
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
251 virgin ones I have pulled from my daily-use Pirelli. Naturally my first version
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
252 of the Mokopir-FFS (then called MysteryFFS) extraction utility expected the root
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
253 node to always be at index #1. But then I got some additional Pirelli phones,
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
254 and discovered that in certain cases, index record #1 is a deleted object (the
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
255 original root node which has been deleted), and the new active root node is
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
256 somewhere in the middle of the index!
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
257
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
258 Thus it appears that in order to find the active root node, one needs to scan
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
259 the active index block linearly from the beginning (disregarding the tree
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
260 structure pointers in this initial pass), looking for a non-deleted object of
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
261 type F2 (a directory) whose corresponding name chunk sports a name beginning
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
262 with the '/' character. (Anyone who's been raised in UNIX will immediately
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
263 know that the path separator character '/' is the only character other than NUL
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
264 that's absolutely forbidden in the individual filenames - so this special
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
265 "root node name" is the only case of a '/' character appearing in what would
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
266 otherwise be a regular filename.)
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
267
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
268 [What causes the root node to be somewhere other than at index #1? I assume it
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
269 has to do with the dirty space reclamation / data movement algorithm. In a
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
270 "virgin" FFS image the very first sector is the active index block, and the
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
271 following sector is the first to hold chunks, beginning with the name chunk of
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
272 the root node. Now what happens if all data in that sector aside from the
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
273 root node name and some other mostly-static directory names becomes dirty,
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
274 i.e., belonging to deleted or overwritten files? How would that flash space
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
275 get reclaimed? I assume that the FFS firmware algorithm moves all still-active
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
276 chunks to a new flash sector, invalidating the old copies - turning the latter
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
277 into deleted objects. The root node will be among them. Then at some point
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
278 the active index block is going to fill up too, and will need to be rewritten
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
279 into a new sector - at which point the previously-deleted index entries are
343b6b2f178b beginning of Mokopir-FFS verbal description
Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
parents:
diff changeset
280 omitted and the root node becomes #1 again...]