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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