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# Copyright (c) 2012 Sean Bartell
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
#
# - Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
# - Redistributions in binary form must reproduce the above copyright
# notice, this list of conditions and the following disclaimer in the
# documentation and/or other materials provided with the distribution.
# - The name of the author may not be used to endorse or promote products
# derived from this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
# OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
# IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
# NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
# THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
# FAT filesystem script.
# Largely based on https://en.wikipedia.org/wiki/File_Allocation_Table
# Currently only FAT12 and FAT16 are supported.
transform u8 = uint8;
transform u16 = uint16le;
transform u32 = uint32le;
transform fat_attributes = struct {
.read_only <- bit;
.hidden <- bit;
.system <- bit;
.volume_label <- bit;
.subdirectory <- bit;
.archive <- bit;
.device <- bit;
.reserved <- bit;
} <- bits_le <- known_length(1);
transform file_data(data, bits, fat, cluster_size, start) = (in.data) <- struct {
.cluster <- (data[(start-2)*cluster_size, cluster_size]);
.last_cluster_number <- switch (bits) {
12: (488); # 0x00000ff8
16: (65528); # 0x0000fff8
32: (268435448); # 0x0ffffff8
};
.next <- (fat[start]);
if (.next == 0 || .next >= .last_cluster_number) {
.data <- (.cluster);
} else {
.rest <- file_data(data, bits, fat, cluster_size, .next) <- known_length(0);
.data <- (.cluster ++ .rest);
}
};
transform fat_dir_entry(data, bits, fat, cluster_size, self_start, parent) = struct {
.filename <- known_length(8);
.extension <- known_length(3);
.attrs <- fat_attributes;
.flags <- u8;
.ctime_fine <- u8;
.ctime <- u16;
.cdate <- u16;
.adate <- u16;
.permissions <- u16;
.mtime <- u16;
.mdate <- u16;
.start <- u16;
.size <- u32;
.size_shown <- if (.size > 32) { (32) } else { (.size) };
if (.start != 0 && .start != self_start && .start != parent && .filename[0] != 229) {
.data
<- if (.attrs.subdirectory) {
repeat { fat_dir_entry(data, bits, fat, cluster_size, .start, self_start) }
} else {
(in[0,.size_shown])
}
<- if (.size != 0) { (in[0,.size]) } else { (in) }
<- file_data(data, bits, fat, cluster_size, .start);
}
};
transform fat_table(bits, num_clusters) = switch (bits) {
12: partial {repeat(num_clusters) { uint_le(12) }} <- bits_le;
16: partial {repeat(num_clusters) { u16 }};
32: partial {repeat(num_clusters) { u32 }};
};
transform fat_super(disk) = struct {
.jump_instruction <- known_length(3);
.oem_name <- ascii <- known_length(8);
# DOS 2.0 BPB
.bytes_per_sector <- u16; # must be power of two, at least 32
.sectors_per_cluster <- u8; # must be power of two
.num_reserved_sectors <- u16;
.num_fats <- u8; # at least 1
.num_root_entries <- u16; # 0 for FAT32
.num_sectors_16 <- u16;
.media_descriptor <- u8;
.sectors_per_fat <- u16; # 0 for FAT32
# DOS 3.0/3.2/3.31 BPB
.sectors_per_track <- u16;
.num_heads <- u16;
# DOS 3.31 BPB
.bpb331 <- struct {
.ignore <- nonzero_boolean <- (.num_sectors_16);
.num_hidden_sectors <- u32;
.num_sectors_32 <- u32;
};
.drive_number <- u8;
.chkdsk_flags <- u8;
.extended_boot_signature <- u8;
if (.extended_boot_signature == 41) {
.volume_id <- u32;
.volume_label <- ascii <- known_length(11);
.type <- ascii <- known_length(8);
}
.boot_signature <- (disk[510,2]); # b"\x55\xaa"; TODO: what if .bytes_per_sector < 512?
};
transform fat_filesystem_tree(disk) = struct {
.super <- partial{fat_super(disk)} <- (disk);
.num_sectors <- if (.super.bpb331.ignore) {
(.super.num_sectors_16)
} else {
(.super.bpb331.num_sectors_32)
};
.cluster_size <- (.super.sectors_per_cluster * .super.bytes_per_sector);
.first_root_sector <- (.super.num_reserved_sectors + .super.num_fats * .super.sectors_per_fat);
.first_data_sector <- (.first_root_sector +
(.super.num_root_entries * 32 + .super.bytes_per_sector - 1) //
.super.bytes_per_sector);
.num_clusters <- (2 + (.num_sectors - .first_data_sector) // .super.sectors_per_cluster);
.bits <- if (.num_clusters < 4085) { (12) }
else { if (.num_clusters < 65525) { (16) } else { (32) } };
.fats <- partial(.super.num_reserved_sectors * .super.bytes_per_sector) {
repeat(.super.num_fats) {
fat_table(.bits, .num_clusters) <-
known_length(.super.sectors_per_fat * .super.bytes_per_sector)
}
} <- (disk);
.root <- partial(.first_root_sector * .super.bytes_per_sector) {
repeat(.super.num_root_entries) {
fat_dir_entry(disk[.first_data_sector * .super.bytes_per_sector:],
.bits, .fats[0], .cluster_size, 0, 0)
}
} <- (disk);
};
transform fat_filesystem = partial {fat_filesystem_tree(in)};
transform main = fat_filesystem;
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