linux-kernel - Re: [PATCH 1/2] affs: generate OFS sequence numbers starting at 1

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Message-ID: <20250226143148.GT5777@suse.cz>
Date: Wed, 26 Feb 2025 15:31:48 +0100
From: David Sterba <dsterba@...e.cz>
To: Simon Tatham <anakin@...ox.com>
Cc: David Sterba <dsterba@...e.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] affs: generate OFS sequence numbers starting at 1

On Thu, Feb 20, 2025 at 08:14:43AM +0000, Simon Tatham wrote:
> 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.
> 
> Signed-off-by: Simon Tatham <anakin@...ox.com>

Thanks for the fixes, I'll send them for merge soon and to stable as
well as they're both real fixes. I found the sequence documented at
https://wiki.osdev.org/FFS_(Amiga) so I added the reference to the
changelog.