[Cbe-oss-dev] [PATCH] ps3rom: sector size should be 512 bytes

[James Bottomley]

On Thu, 2008-01-31 at 06:10 -0800, Nicholas A. Bellinger wrote:
> Greetings Geert and Co,
> 
> I have a related patch that I have been using with ps3rom.c for some
> time that fixes a bug in fs/bio.c that assumes 512 byte sectors for
> ATAPI operations.  This bug actually exists for all non 512 byte sector
> devices go through this code path (I found it with
> scsi_execute_async()), but I first ran into this issue with ps3rom.c
> because max_sectors (32) is small enough to trigger the bug assuming 512
> byte sectors during typical ATAPI READ_10 ops with iSCSI/HD.  Because
> typical max_sector settings for libata and USB are much higher, I have
> never ran into this issue outside of ps3rom.c, but the bug exists
> nevertheless..
> 
> The current patch assumes 512 byte sectors, and adds a sector_size
> parameter to drivers/scsi/scsi_lib.c:scsi_req_map_sg() to change it for
> passed struct request.  I know that some folks talked about killing
> scsi_execute_async() and fixing this problem elsewhere, but until then
> please consider this patch.  Any input is also appreciated.

My first reaction is really, no; there's no way we should be doing such
a nasty layering violation.

The block code is set up to work with 512 byte sectors for its internal
counts.  Something like this will damage all non-512 byte sector devices
(and we do have several of those).

There are three quantities you need to understand when trying to do
something like this

     1. The actual internal block sector size for sector counts.  This
        is hard coded to 512
     2. The medium sector size.  This is stored in hardsect_size in the
        queue.  Block ensures that it always sends down enough 512 byte
        sectors to be a multiple of this
     3. The block size.  This represents the unit the user of the device
        wants to think in terms of (most often for filesystems, the fs
        block size). It's stored in various places including the
        block_device bd_block_size.

It really sounds like the problem with ps3rom is that hardsect_size
isn't being set correctly.  As I understand the problem, from the
incredibly cursory insight the emails give, so please correct if wrong,
you want the hard sector size to be the CD_FRAMESIZE?

James