Re: [PATCH] Revert "ata: libata-scsi: Honor the D_SENSE bit for CK_COND=1 and no error"

[Ian Pilcher <arequipeno@gmail.com>]

On 8/13/24 8:19 AM, Niklas Cassel wrote:
> This reverts commit 28ab9769117ca944cb6eb537af5599aa436287a4.
> 
> Sense data can be in either fixed format or descriptor format.
> 
> SAT-6 revision 1, "10.4.6 Control mode page", defines the D_SENSE bit:
> "The SATL shall support this bit as defined in SPC-5 with the following
> exception: if the D_ SENSE bit is set to zero (i.e., fixed format sense
> data), then the SATL should return fixed format sense data for ATA
> PASS-THROUGH commands."
> 
> The libata SATL has always kept D_SENSE set to zero by default. (It is
> however possible to change the value using a MODE SELECT SG_IO command.)
> 
> Failed ATA PASS-THROUGH commands correctly respected the D_SENSE bit,
> however, successful ATA PASS-THROUGH commands incorrectly returned the
> sense data in descriptor format (regardless of the D_SENSE bit).
> 
> Commit 28ab9769117c ("ata: libata-scsi: Honor the D_SENSE bit for
> CK_COND=1 and no error") fixed this bug for successful ATA PASS-THROUGH
> commands.
> 
> However, after commit 28ab9769117c ("ata: libata-scsi: Honor the D_SENSE
> bit for CK_COND=1 and no error"), there were bug reports that hdparm,
> hddtemp, and udisks were no longer working as expected.
> 
> These applications incorrectly assume the returned sense data is in
> descriptor format, without even looking at the RESPONSE CODE field in the
> returned sense data (to see which format the returned sense data is in).
> 
> Considering that there will be broken versions of these applications around
> roughly forever, we are stuck with being bug compatible with older kernels.

I suppose it's a small quibble, but I don't think it's fair to say that
the applications are behaving incorrectly.  They assume that the
returned sense data is in descriptor format because it always was.  That
doesn't seem unreasonable.

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