E.5. sg driver
The following header files in the kernel source are relevant to the sg driver:
/usr/src/linux/include/scsi/sg.h
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As pointed out in Section E.1 this is best included in
applications by using:
#include <linux/../scsi/sg.h>
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E.5.1. sg compile options
Here are some defines from the sg.h file that the user could conceivably want
to change. The current default values are shown in braces on the right:
SG_SCATTER_SZ {32768}
SG_DEF_RESERVED_SIZE {SG_SCATTER_SZ}
SG_DEF_FORCE_LOW_DMA {0}
SG_DEF_FORCE_PACK_ID {0}
SG_DEF_KEP_ORPHAN {0}
SG_MAX_QUEUE {16}
SG_DEFAULT_RETRIES {1} # i.e. don't retry
SG_BIG_BUFF {SG_DEF_RESERVED_SIZE}
SG_DEFAULT_TIMEOUT {60 seconds}
SG_DEF_COMMAND_Q {0 *}
SG_DEF_UNDERRUN_FLAG {0}
* The per file descriptor copy of this flips to 1 (thus
allowing command queuing) as soon as a write() based
on the newer sg_io_hdr structure is detected.
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E.5.2. sg ioctls and user interface
The following ioctl()s are listed in alphabetical order with a brief
explanation to the right. [See sg documentation for more details.]
SG_EMULATED_HOST [indicate if adapter is ide-scsi]
SG_GET_COMMAND_Q [command queuing flag state]
SG_GET_KEEP_ORPHAN [interrupted SG_IO keep orphan flag state]
SG_GET_LOW_DMA ["low dma flag" (<= 16 MB on i386) state]
SG_GET_NUM_WAITING [number of responses waiting to be read()]
SG_GET_PACK_ID [pack_id of next to read() response
(-1 if none)]
SG_GET_REQUEST_TABLE [yields array of requests being processed]
SG_GET_RESERVED_SIZE [current size of reserved buffer]
SG_GET_SCSI_ID [a little more info than the mid level's
SCSI_IOCTL_GET_IDLUN ioctl]
SG_GET_SG_TABLESIZE [max entries in host's scatter gather table]
SG_GET_TIMEOUT [yields timeout (unit: jiffies
(10ms on i386))]
SG_GET_TRANSFORM [state of ide-scsi's transform flag]
SG_IO [send given SCSI command and wait for
response]
SG_NEXT_CMD_LEN [change command length of next command]
SG_SCSI_RESET [send a SCSI bus, device or host reset]
SG_SET_COMMAND_Q [set command queuing state {old=0, new=1}]
SG_SET_DEBUG [set debug level {0}]
SG_SET_KEEP_ORPHAN [set SG_IO's keep orphan flag {0}]
SG_SET_FORCE_LOW_DMA [force DMA buffer low (<= 16 MB on i386)
{0}]
SG_SET_FORCE_PACK_ID [so read() can fetch by pack_id {0}]
SG_SET_RESERVED_SIZE [change default buffer size
{SG_DEF_RESERVED_SIZE}]
SG_SET_TIMEOUT [change current timeout {60 secs} ]
SG_SET_TRANSFORM [set ide-scsi's ATAPI transform flag {0}]
open() [recognized oflags: O_RDONLY, O_RDWR, O_EXCL,
O_NONBLOCK]
close()
read()
write()
ioctl()
poll() [used when in O_NONBLOCK mode]
fasync() [enables generation of SIGIO signal for read()]
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