/* SPDX-License-Identifier: GPL-1.0+ WITH Linux-syscall-note */ /* pg.h (c) 1998 Grant R. Guenther <grant@torque.net> Under the terms of the GNU General Public License
pg.h defines the user interface to the generic ATAPI packet command driver for parallel port ATAPI devices (pg). The driver is loosely modelled after the generic SCSI driver, sg, although the actual interface is different.
The pg driver provides a simple character device interface for sending ATAPI commands to a device. With the exception of the ATAPI reset operation, all operations are performed by a pair of read and write operations to the appropriate /dev/pgN device. A write operation delivers a command and any outbound data in a single buffer. Normally, the write will succeed unless the device is offline or malfunctioning, or there is already another command pending. If the write succeeds, it should be followed immediately by a read operation, to obtain any returned data and status information. A read will fail if there is no operation in progress.
As a special case, the device can be reset with a write operation, and in this case, no following read is expected, or permitted.
There are no ioctl() operations. Any single operation may transfer at most PG_MAX_DATA bytes. Note that the driver must copy the data through an internal buffer. In keeping with all current ATAPI devices, command packets are assumed to be exactly 12 bytes in length.
To permit future changes to this interface, the headers in the read and write buffers contain a single character "magic" flag. Currently this flag must be the character "P".
char magic; /* == PG_MAGIC */ char func; /* PG_RESET or PG_COMMAND */ int dlen; /* number of bytes expected to transfer */ int timeout; /* number of seconds before timeout */ char packet[12]; /* packet command */
};
struct pg_read_hdr {
char magic; /* == PG_MAGIC */ char scsi; /* "scsi" status == sense key */ int dlen; /* size of device transfer request */ int duration; /* time in seconds command took */ char pad[12]; /* not used */
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