scsi: sd: Enable modern protocol features on more devices
Due to legacy USB devices having a tendency to either lock up or
return garbage if one attempts to query device capabilities, the USB
transport disables VPD pages by default. This prevents discard from
being properly configured on most modern USB-attached SSDs.
Introduce two additional heuristics to determine whether VPD pages
should be consulted.
The first heuristic fetches VPD pages if a device reports that Logical
Block Provisioning is enabled. It is very unusual for a device to
support thin provisioning and not provide the associated VPDs.
Consequently, if a device reports that Logical Block Provisioning is
enabled (LBPME) in READ CAPACITY(16) response, the scsi_device has no
VPDs attached, and the reported SPC version is larger than 3, then an
attempt will be made to read the VPD pages during revalidate.
The second heuristic relies on the fact that almost all modern devices
return a set of version descriptors in the INQUIRY response. These
descriptors outline which version of various protocol features are
supported. If a device manufacturer has gone through the effort of
filling out compliance descriptors, it is highly unlikely that VPD
pages are not supported. So if a device provides version descriptors
in the INQUIRY response, the scsi_device has no VPDs attached, and the
reported SBC version is larger than 2, then an attempt will be made to
read the VPD pages. In addition, READ CAPACITY(16) will be preferred
over READ CAPACITY(10) to facilitate accessing the LBPME flag.
The benefit to relying on INQUIRY is that it is data we already
have. We do not have to blindly poke the device for additional
information and risk confusing it.
Extracting the SBC version is done by a new helper, sd_sbc_version().
Another helper is provided to determine whether a scsi_device has VPD
pages attached or not.
Reported-by: Aman Karmani <aman@tmm1.net>
Tested-by: Aman Karmani <aman@tmm1.net>
Reported-by: David Sebek <dasebek@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
4 files changed
