In an ideal world, we would use the existing ATA_12 opcode
to issue 12-byte ATA passthrough commands for libata ATAPI drives
from userspace.
But ATA_12 happens to have the same SCSI opcode value as the older
CD/RW "BLANK" command, widely used by cdrecord and friends.
So, to achieve ATA passthru capability for libata ATAPI,
we have to instead use the ATA_16 opcode: a 16-byte command.
SCSI normally disallows issuing 16-byte commands to 12-byte devices,
so special support has to be added for this.
Introduce an "allow_ata_16" boolean to the scsi_host struct.
This provides a means for libata to signal that 16-byte ATA_16
commands should be permitted even for 12-byte ATAPI devices.
Signed-off-by: Mark Lord <mlord@xxxxxxxxx>
--- old/include/scsi/scsi_host.h 2007-01-02 19:06:45.000000000 -0500
+++ new/include/scsi/scsi_host.h 2007-01-02 19:09:06.000000000 -0500
@@ -608,6 +608,13 @@
unsigned async_scan:1;
/*
+ * True for libata, to allow issuing ATA_16 16-byte CDBs
+ * to (otherwise) 12-byte ATAPI drives. ATAPI cannot use
+ * the ATA_12 opcode, because it means "BLANK" to CDRW drives.
+ */
+ unsigned allow_ata_16:1;
+
+ /*
* Optional work queue to be utilized by the transport
*/
char work_q_name[KOBJ_NAME_LEN];
--- old/drivers/scsi/scsi.c 2007-01-02 19:06:45.000000000 -0500
+++ new/drivers/scsi/scsi.c 2007-01-02 19:09:06.000000000 -0500
@@ -567,12 +567,17 @@
* length exceeds what the host adapter can handle.
*/
if (CDB_SIZE(cmd) > cmd->device->host->max_cmd_len) {
- SCSI_LOG_MLQUEUE(3,
+ /* permit ATA_16 passthru to 12-byte ATAPI devices */
+ if (cmd->cmnd[0] != ATA_16
+ || CDB_SIZE(cmd) != 16
+ || !cmd->device->host->allow_ata_16) {
+ SCSI_LOG_MLQUEUE(3,
printk("queuecommand : command too long.\n"));
- cmd->result = (DID_ABORT << 16);
+ cmd->result = (DID_ABORT << 16);
- scsi_done(cmd);
- goto out;
+ scsi_done(cmd);
+ goto out;
+ }
}
spin_lock_irqsave(host->host_lock, flags);
--- old/drivers/ata/libata-core.c 2007-01-02 19:06:44.000000000 -0500
+++ new/drivers/ata/libata-core.c 2007-01-02 19:09:06.000000000 -0500
@@ -5686,6 +5686,7 @@
shost->max_lun = 1;
shost->max_channel = 1;
shost->max_cmd_len = 12;
+ shost->allow_ata_16 = 1;
}
/**
-
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