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fstype: make copy of first sector in /env to avoid unaligned reads on the disk (for devfs)

devfs crypto partitions do not support unaligned reads,
so we make a copy of the first in /env/block and then
slice it to find filesystem signatures.

thanks mykhal for reporting the issue.

--- a/rc/bin/fstype

+++ b/rc/bin/fstype

@@ -6,15 +6,16 @@

 	echo 9660

 	exit

 }

+dd -if $1 -count 1 >/env/block >[2]/dev/null

 fn fat {

-	m=`{dd -if $1 -bs 1 -count 3 -skip $2 >[2]/dev/null}

+	m=`{dd -if /env/block -bs 1 -count 3 -skip $1 >[2]/dev/null}

 	~ $"m FAT

 }

-if(fat $1 54 || fat $1 82){

+if(fat 54 || fat 82){

 	echo dos

 	exit

 }

-m=`{dd -if $1 -bs 4 -count 1 >[2]/dev/null | xd | sed 's,0000000  ,,;q'}

+m=`{dd -if /env/block -bs 4 -count 1 >[2]/dev/null | xd | sed 's,0000000  ,,;q'}

 if(~ $"m 529ab12b){

 	echo paqfs

 	exit

@@ -23,13 +24,12 @@

 	echo hjfs

 	exit

 }

-m=`{dd -if $1 -bs 16 -count 1 -skip 16 >[2]/dev/null}

+m=`{dd -if /env/block -bs 16 -count 1 -skip 16 >[2]/dev/null}

 if(~ $"m 'kfs wren device'){

 	echo kfs

 	exit

 }

-dd -if $1 -count 1 >[2]/dev/null | \

-awk '

+</env/block awk '

 /^(blocksize|daddrbits|daddrbits|indirblks|dirblks|namelen)/{p[$1]=$2}

 END{

 	ca["fs", "blocksize"] = 4*1024

-- 

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