affs: generate OFS sequence numbers starting at 1

[ Upstream commit e4cf8ec ]

If I write a file to an OFS floppy image, and try to read it back on
an emulated Amiga running Workbench 1.3, the Amiga reports a disk
error trying to read the file. (That is, it's unable to read it _at
all_, even to copy it to the NIL: device. It isn't a matter of getting
the wrong data and being unable to parse the file format.)

This is because the 'sequence number' field in the OFS data block
header is supposed to be based at 1, but affs writes it based at 0.
All three locations changed by this patch were setting the sequence
number to a variable 'bidx' which was previously obtained by dividing
a file position by bsize, so bidx will naturally use 0 for the first
block. Therefore all three should add 1 to that value before writing
it into the sequence number field.

With this change, the Amiga successfully reads the file.

For data block reference: https://wiki.osdev.org/FFS_(Amiga)

Signed-off-by: Simon Tatham <[email protected]>
Signed-off-by: David Sterba <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
(cherry picked from commit 739499e146320eec6dc3ae27f993e22955c0e932)
Signed-off-by: Alok Tiwari <[email protected]>

Author: sgtatham

fs/affs/file.c

@@ -596,7 +596,7 @@ affs_extent_file_ofs(struct inode *inode, u32 newsize)
 		BUG_ON(tmp > bsize);
 		AFFS_DATA_HEAD(bh)->ptype = cpu_to_be32(T_DATA);
 		AFFS_DATA_HEAD(bh)->key = cpu_to_be32(inode->i_ino);
-		AFFS_DATA_HEAD(bh)->sequence = cpu_to_be32(bidx);
+		AFFS_DATA_HEAD(bh)->sequence = cpu_to_be32(bidx + 1);
 		AFFS_DATA_HEAD(bh)->size = cpu_to_be32(tmp);
 		affs_fix_checksum(sb, bh);
 		bh->b_state &= ~(1UL << BH_New);
@@ -746,7 +746,7 @@ static int affs_write_end_ofs(struct file *file, struct address_space *mapping,
 		if (buffer_new(bh)) {
 			AFFS_DATA_HEAD(bh)->ptype = cpu_to_be32(T_DATA);
 			AFFS_DATA_HEAD(bh)->key = cpu_to_be32(inode->i_ino);
-			AFFS_DATA_HEAD(bh)->sequence = cpu_to_be32(bidx);
+			AFFS_DATA_HEAD(bh)->sequence = cpu_to_be32(bidx + 1);
 			AFFS_DATA_HEAD(bh)->size = cpu_to_be32(bsize);
 			AFFS_DATA_HEAD(bh)->next = 0;
 			bh->b_state &= ~(1UL << BH_New);
@@ -780,7 +780,7 @@ static int affs_write_end_ofs(struct file *file, struct address_space *mapping,
 		if (buffer_new(bh)) {
 			AFFS_DATA_HEAD(bh)->ptype = cpu_to_be32(T_DATA);
 			AFFS_DATA_HEAD(bh)->key = cpu_to_be32(inode->i_ino);
-			AFFS_DATA_HEAD(bh)->sequence = cpu_to_be32(bidx);
+			AFFS_DATA_HEAD(bh)->sequence = cpu_to_be32(bidx + 1);
 			AFFS_DATA_HEAD(bh)->size = cpu_to_be32(tmp);
 			AFFS_DATA_HEAD(bh)->next = 0;
 			bh->b_state &= ~(1UL << BH_New);