SG_IO ioctl for block devices
Subsystems (2)
PATCH 1/1 SG_IO ioctl for block devices
I have been playing around with the SG_IO ioctl() that recently appeared in drivers/block/scsi_ioctl.c .
First a warning: using sg's write()/read() interface is a dangerous thing to do to anything other than an sg device (especially a disk). The utilities in sg3_utils (and sg_utils) took the precaution of sending a "sg" ioctl and assumed if it worked then the file descriptor referred to a sg device. Now _all_ block devices respond to the ioctl()s I chose :-(
IMO sg's write()/read() interface is still useful for queuing and high speed applications. However for the great majority of cases the SG_IO ioctl is sufficient. It turns out that sg3_utils version 1.01 doesn't scribble on disks (as outlined above), more by luck than good management. Several things fail (e.g. sg_logs) that can easily be fixed while sg_inq and sg_dd work. [sg_dd works because it treats /dev/sda as a normal file rather than a sg device.] I will release sg3_utils version 1.02 shortly.
The error processing of the SG_IO ioctl() is broken as far as I can determine. My attached patch drives output values to 0 (their inert values) and rescues the scsi status value from the scsi_request structure. Notice the hack in drivers/scsi/scsi_lib.c to stop the gratuitous clearing of req->errors. The sense buffer is not conveyed into struct request and there seems to be no code in scsi_lib.c to do that.
To keep the block SG_IO consistent with sg's version, I removed the EIO errno conditions. CHECK CONDITION does not (necessarily) indicate an error. Witness the code fix around lk 2.4.18 to correctly handle RECOVERED_ERROR. So a return value of zero implies that a consistent set of values has been written back into the sg_io_hdr instance (and the application best check them).
The patch is against lk 2.5.50bk3
Doug Gilbert
drivers/block/scsi_ioctl.c2550sgio1 renamed from drivers/block/scsi_ioctl.c +23 -12
@@ -126,7 +126,7 @@ struct sg_io_hdr *uptr) { unsigned long uaddr, start_time; - int err, reading, writing, nr_sectors; + int reading, writing, nr_sectors; struct sg_io_hdr hdr; struct request *rq; struct bio *bio;
@@ -265,26 +265,36 @@ start_time = jiffies; - /* - * return -EIO if we didn't transfer all data, caller can look at - * residual count to find out how much did succeed + /* ignore return value. All information is passed back to caller + * (if he doesn't check that is his problem). + * N.B. a non-zero SCSI status is _not_ necessarily an error. */ - err = blk_do_rq(q, bdev, rq); - if (rq->data_len > 0) - err = -EIO; + blk_do_rq(q, bdev, rq); if (bio) { bio_unmap_user(bio, reading); bio_put(bio); } - hdr.status = rq->errors; + /* write to all output members */ + hdr.status = rq->errors; + hdr.masked_status = (hdr.status >> 1) & 0x1f; + hdr.msg_status = 0; + hdr.host_status = 0; + hdr.driver_status = 0; + hdr.info = 0; + if (hdr.masked_status || hdr.host_status || hdr.driver_status) + hdr.info |= SG_INFO_CHECK; hdr.resid = rq->data_len; hdr.duration = (jiffies - start_time) * (1000 / HZ); + hdr.sb_len_wr = 0; if (rq->sense_len && hdr.sbp) { - if (!copy_to_user(hdr.sbp,rq->sense, rq->sense_len)) - hdr.sb_len_wr = rq->sense_len; + int len = (hdr.mx_sb_len < rq->sense_len) ? + hdr.mx_sb_len : rq->sense_len; + + if (!copy_to_user(hdr.sbp, rq->sense, len)) + hdr.sb_len_wr = len; } blk_put_request(rq);
@@ -297,8 +307,9 @@ kfree(buffer); } - - return err; + /* may not have succeeded, but output values written to control + * structure (struct sg_io_hdr). */ + return 0; } #define FORMAT_UNIT_TIMEOUT (2 * 60 * 60 * HZ)
drivers/scsi/scsi_lib.c2550bk3sgio1 renamed from drivers/scsi/scsi_lib.c +7 -2
@@ -441,6 +441,7 @@ int this_count = SCpnt->bufflen >> 9; request_queue_t *q = &SCpnt->device->request_queue; struct request *req = SCpnt->request; + int clear_errors = 1; /* * We must do one of several things here:
@@ -481,9 +482,12 @@ } if (blk_pc_request(req)) { - req->errors = result & 0xff; + req->errors = (driver_byte(result) & DRIVER_SENSE) ? + (CHECK_CONDITION << 1) : (result & 0xff); if (!result) req->data_len -= SCpnt->bufflen; + else + clear_errors = 0; } /*
@@ -504,7 +508,8 @@ req->nr_sectors, good_sectors)); SCSI_LOG_HLCOMPLETE(1, printk("use_sg is %d\n ", SCpnt->use_sg)); - req->errors = 0; + if (clear_errors) + req->errors = 0; /* * If multiple sectors are requested in one buffer, then * they will have been finished off by the first command.