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176 lines
7.4 KiB
176 lines
7.4 KiB
BREAK <MFT Definitions>
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;** MSDOS MFT definitions
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;
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; The Master File Table (MFT) associates the cannonicalized pathnames, lock
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; records and SFTs for all files open on this machine.
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;
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; The MFT implementation employs a single memory buffer which is used from
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; both ends. This gives the effect (at least until they run into each
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; other) of two independent buffers.
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;
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; MFT buffer
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; ==========
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; The MFT buffer contains MFT name records and free space. It uses a
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; classic heap architecture: freed name records are marked free and
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; conglomerated with any adjacent free space. When one is to create a name
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; entry the free list is searched first-fit. The list of name and free
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; records is always terminated by a single END record.
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;
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; LOCK buffer
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; ===========
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; The lock buffer contains fixed format records containing record locking
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; information. Since they are fixed format the space is handled as a series
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; of chains: one for each MFT name record and one for the free list. No
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; garbage collection is necessary.
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;
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; Space allocation
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; ================
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; The MFT is managed as a heap. Empty blocks are allocated on a first-fit
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; basis. If there is no single large enough empty block the list is garbage
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; collected.
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;
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; MFT name records:
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;
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; 8 16 8 16 32 16 n
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; |------|-----|-----|------|------|------|---------~~~~~~---------|
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; | FLAG | LEN | SUM | LPTR | SPTR | SERL | <.asciz string> |
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; --------------------------------------------------~~~~~~----------
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;
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; FLAG = record type flag
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; LEN = total byte length of record.
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; SUM = sum of bytes in asciz string. Used to speed
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; searches
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; LPTR= pointer to first record in lock chain segment
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; is MFT segment
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; SPTR= pointer to first sft in sft chain
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; SERL= serial number
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; <string> = name string, zero-byte terminated. There
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; may be garbage bytes following the 00 byte;
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; these are counted in the LEN field.
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;
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;
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; MFT free records
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;
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; 8 16
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; |------|-----|----~~~~~~~~~~~~~~~~~~~~~~~~~~~---------|
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; | FLAG | LEN | free |
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; ------------------~~~~~~~~~~~~~~~~~~~~~~~~~~~----------
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;
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; FLAG = record type flag
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; LEN = total byte length of record.
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;
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;
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; MFT END records
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;
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; 8
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; |------|
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; | FLAG |
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; --------
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;
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; FLAG = record type flag
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;** MFT definitions
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;*
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;* NOTE: the flag and length fields are identical for all record types
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;* (except the END type has no length) This must remain so as
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;* some code depends upon it.
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;*
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;* NOTE: Many routines check for "n-1" of the N flag values and if no
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;* match is found assume the flag value must be the remaining
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;* possibility. If you add or remove flag values you must check
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;* all references to mft_flag.
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MFT_entry STRUC
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mft_flag DB ? ; flag/len field
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mft_len DW ?
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mft_sum DB ? ; string sum word
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mft_lptr DW ? ; LCK pointer
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mft_sptr DD ? ; sft pointer
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mft_serl DW ? ; serial number
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mft_name DB ? ; offset to start of name
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MFT_entry ENDS
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MFLG_NAM EQU 1 ; min value for name record
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MFLG_FRE EQU 0 ; free record
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MFLG_END EQU -1 ; end record
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;* Record Lock Record (RLR):
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;
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; 16 32 32 32
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; |-------|--------|--------|--------|
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; | NEXT | FBA | LBA | SPTR |
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; | | lo hi | lo hi | |
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; ------------|--------|--------------
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;
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; CHAIN = pointer to next RLR. 0 if end
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; FBA = offset of 1st byte of locked region
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; LBA = offset of last byte of locked region
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; SPTR = pointer to SFT lock was issued on
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RLR_entry STRUC
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rlr_next DW ? ; chain to next RLR, 0 if end
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rlr_fba DW ? ; first byte addr (offset) of reigion
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DW ?
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rlr_lba DW ? ; last byte addr of region
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DW ?
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rlr_sptr DD ? ; SFT pointer
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rlr_pid dw ? ; process id of issuer
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rlr_type dw ? ; lock type
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RLR_entry ENDS
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rlr_lall equ 00h ; lock all ops
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rlr_lwr equ 01h ; lock write ops
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;
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; A pictorial diagram for the linkages is as follows:
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;
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; +---sptr------+
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; V |
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; +---+<----------|---sptr------+------------+
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; |SFT+----+ | | |
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; +-+-+ | +-+-+ +--+-+ +--+-+
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; V +--->|MFT+-lptr->-|LOCK+-next->|LOCK+->0
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; +---+ | +---+ +----+ +----+
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; |SFT+----+ ^
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; +-+-+ |
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; | |
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; +-------------+
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;
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;
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;**
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;
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; Interesting behavior should be noted:
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;
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; The sharer must maintain information on files in three forms:
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;
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; local/remote handles. These are normal handles and behave in no
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; strange manner. They are identified by SF_mode not having the
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; sfIsFCB flag nor by having the sf_mode = 70. No problems with
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; locking. No problems with open. No problems with close.
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; CloseByName will iterate closes until the mft disappears.
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; CloseUser will iterate closes until no SFT for the particular user
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; appears. CloseProcess will iterate closes until no SFT for the
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; particular user/process appears.
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;
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; local FCBs. There are no corresponding SFT's for these as the SFTs
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; are cached but will be valid for the particular file. There is
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; one SFT for each open on a file by a specific process. These are
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; identified the sfIsFCB flag in the sf_mode field. When multiple
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; opens occur, we merely find the sf pertinent to the file and
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; process. Close decrements the ref count. CloseByName, CloseUser,
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; CloseProcess will iterate closes until no more SFTs exist.
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;
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; handles with mode 70. These represent FCB's open across the network.
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; As such, identical sfts may have been collapsed by the $open code.
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; This results in a reuse of the same SFT. The $Open code must
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; correctly set the ref-count for the sft to reflect the number of
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; collapses that have occurred. These are identified by a 70 in the
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; SF_mode field. There can be no locking on these SFTs. Open must
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; scan the list of SFTs for the file and increment its ref count
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; appropriately.
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