ataide_buf Structure

The ataide_buf structure is used for communication between the IDE device driver and the IDE adapter device driver during an initiator I/O request. This structure is passed to and from the strategy routine in the same way a standard driver uses a struct buf structure.

Fields in the ataide_buf Structure

The ataide_buf structure contains certain fields used to pass an IDE command and associated parameters to the IDE adapter device driver. Other fields within this structure are used to pass returned status back to the IDE device driver. The ataide_buf structure is defined in the /usr/include/sys/ide.h file.

Fields in the ataide_buf structure are used as follows:

1. Reserved fields should be set to a value of 0, except where noted.
2. The bufstruct field contains a copy of the standard buf buffer structure that documents the I/O request. Included in this structure, for example, are the buffer address, byte count, and transfer direction. The b_work field in the buf structure is reserved for use by the IDE adapter device driver. The current definition of the buf structure is in the /usr/include/sys/buf.h include file.
3. The bp field points to the original buffer structure received by the IDE device driver from the caller, if any. This can be a chain of entries in the case of spanned transfers (IDE commands that transfer data from or to more than one system-memory buffer). A null pointer indicates a nonspanned transfer. The null value specifically tells the IDE adapter device driver all the information needed to perform the DMA data transfer is contained in the bufstruct fields of the ataide_buf structure. If the bp field is set to a non-null value, the ataide_buf.sg_ptr field must have a value of null, or else the operation is not allowed.
4. The ata field, defined as an ata_cmd structure, contains the IDE command (ATA or ATAPI), status, error indicator, and a flag variable:
   • The flags field contains the following bit flags:

     ATA_CHS_MODE	Execute the command in cylinder head sector mode.
     ATA_LBA_MODE	Execute the command in logical block addressing mode.
     ATA_BUS_RESET	Reset the ATA bus, ignore the current command.

   • The command field is the IDE ATA command opcode. For ATAPI packet commands, this field must be set to ATA_ATAPI_PACKET_COMMAND (0xA1).
   • The device field is the IDE indicator for either the master (0) or slave (1) IDE device.
   • The sector_cnt_cmd field is the number of sectors affected by the command. A value of zero usually indicates 256 sectors.
   • The startblk field is the starting LBA or CHS sector.
   • The feature field is the ATA feature register.
   • The status field is an output parameter indicating the ending status for the command. This field is updated by the IDE adapter device driver upon completion of a command.
   • The errval field is the error type indicator when the ATA_ERROR bit is set in the status field. This field has slightly different interpretations for ATA and ATAPI commands.
   • The sector_cnt_ret field is the number of sectors not processed by the device.
   • The endblk field is the completion LBA or CHS sector.
   • The atapi field is defined as an atapi_command structure, which contains the IDE ATAPI command. The 12 or 16 bytes of a single IDE command are stored in consecutive bytes, with the opcode identified individually. The atapi_command structure contains the following fields:
   • The length field is the number of bytes in the actual IDE command. This is normally 12 or 16 (decimal).
   • The packet.op_code field specifies the standard IDE ATAPI opcode for this command.
   • The packet.bytes field contains the remaining command-unique bytes of the IDE ATAPI command block. The actual number of bytes depends on the value in the length field.
5. The sg_ptr field is set to a non-null value to indicate a request for a gathered write. A gathered write means the IDE command conducts a system-to-device data transfer where multiple, noncontiguous system buffers contain the write data. This data is transferred in order as a single data transfer for the IDE command in this ataide_buf structure.

   The contents of the sg_ptr field, if non-null, must be a pointer to the uio structure that is passed to the IDE device driver. The IDE adapter device driver treats the sg_ptr field as a pointer to a uio structure that accesses the iovec structures containing pointers to the data. There are no address-alignment restrictions on the data in the iovec structures. The only restriction is that the total transfer length of all the data must not exceed the maximum transfer length for the adapter device driver.

   The ataide_buf.bufstruct.b_un.b_addr field normally contains the starting system-buffer address and is ignored and can be altered by the IDE adapter device driver when the ataide_buf is returned. The ataide_buf.bufstruct.b_bcount field should be set by the caller to the total transfer length for the data.

6. The timeout_value field specifies the time-out limit (in seconds) to be used for completion of this command. A time-out value of 0 means no time-out is applied to this I/O request.
7. The status_validity field contains an output parameter that can have the following bit flags as a value:

   ATA_IDE_STATUS	The ata.status field is valid.
   ATA_ERROR_VALID	The ata.errval field contains a valid error indicator.
   ATA_CMD_TIMEOUT	The IDE adapter driver caused the command to time out.
   ATA_NO_DEVICE_RESPONSE	The IDE device is not ready.
   ATA_IDE_DMA_ERROR	The IDE adapter driver encountered a DMA error.
   ATA_IDE_DMA_NORES	The IDE adapter driver was not able to transfer entire request. The bufstruct.b_resid contains the count not transferred.

If an error is detected during execution of an IDE command, and the error prevented the IDE command from actually being sent to the IDE bus by the adapter, then the error should be processed or recovered, or both, by the IDE adapter device driver.

If it is recovered successfully by the IDE adapter device driver, the error is logged, as appropriate, but is not reflected in the ata.errval byte. If the error cannot be recovered by the IDE adapter device driver, the appropriate ata.errval bit is set and the ataide_buf structure is returned to the IDE device driver for further processing.

If an error is detected after the command was actually sent to the IDE device, then it should be processed or recovered, or both, by the IDE device driver.

For error logging, the IDE adapter device driver logs IDE bus- and adapter-related conditions, while the IDE device driver logs IDE device-related errors. In the following description, a capital letter "A" after the error name indicates that the IDE adapter device driver handles error logging. A capital letter "H" indicates that the IDE device driver handles error logging.

Some of the following error conditions indicate an IDE device failure. Others are IDE bus- or adapter-related.