71 lines
1.6 KiB
Plaintext
71 lines
1.6 KiB
Plaintext
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#!/usr/bin/perl
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# clear btrfs signature from a device
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use Fcntl;
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use constant BTRFS_SUPER_INFO_OFFSET => 64 * 1024;
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use constant BTRFS_SUPER_INFO_SIZE => 4096;
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use constant BTRFS_SUPER_MIRROR_MAX => 3;
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use constant BTRFS_SUPER_MIRROR_SHIFT => 12;
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use constant BTRFS_MAGIC => "_BHRfS_M";
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use constant BTRFS_DEAD => '_BHRf$_M';
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sub btrfs_sb_offset($) {
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my $mirror =$_[0];
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my $start = 16 * 1024;
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if ($mirror>0) {
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return $start << (BTRFS_SUPER_MIRROR_SHIFT * $mirror);
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}
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return BTRFS_SUPER_INFO_OFFSET;
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}
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my $dbg=1;
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my $savesb=0;
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# main
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my $dev=$ARGV[0];
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my $size;
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if(!-b $dev) {
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print("Not a block device: $dev\n");
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$size=(stat($dev))[7];
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} else {
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$size=`blkdev --getsize64 "$dev"`;
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}
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sysopen(F, $dev, O_EXCL | O_RDWR) or die("Cannot open $dev exclusively: $!");
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sysseek(F, 0, 2);
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$size=tell(F);
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print("Device size: $size\n") if($dbg);
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for(my $i=0;$i<6;$i++) {
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my $off=btrfs_sb_offset($i);
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if($off > $size) {
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print("Offset for SB $i beyond EOF\n") if($dbg);
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last;
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}
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print("Offset $i is $off\n") if($dbg);
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sysseek(F, $off, 0);
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sysread(F, $buf, BTRFS_SUPER_INFO_SIZE);
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if($savesb) {
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open(Q,">SB$i");
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print Q ($buf);
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close(Q);
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}
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my $sbmagic=substr($buf, 0x40, length(BTRFS_MAGIC));
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print("SB magic: $sbmagic\n") if($dbg);
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if(BTRFS_MAGIC eq $sbmagic) {
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print("Found a valid signature of superblock $i\n");
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sysseek(F, $off + 0x40, 0);
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print("Clearing...\n");
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syswrite(F, BTRFS_DEAD, length(BTRFS_DEAD));
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} elsif(BTRFS_DEAD eq $sbmagic) {
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print("Found a signature of a dead superblock $i\n");
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} else {
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print("Superblock $i does not look like a btrfs one\n");
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}
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}
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close(F);
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print("Syncing dev\n");
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system("fsync \'$dev\'");
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