[PATCH] sg.c to set direction more reliably (was Re: [PATCH] fusion update to current APIs)

[Jeremy Higdon <jeremy@sgi.com>]

Okay, here's my proposed patch to sg.

If it's able to determine the direction based on the input and output
buffer sizes, it uses those.  If both input and output buffer sizes
are non-zero, then it resorts to the command bytes.  Folks familiar
with the mptscsi driver will recognize the sg_direction function :-)

I've tested this using sg_utils, and it seems to work, but those are
probably well-behaved.  I will endeavor to test tomorrow with some
RAID utilities that have not been well-behaved, in conjunction with
removing the direction-override code from the host driver.

If this works, then we can remove the nasty direction code from all
the host drivers.

jeremy


===== drivers/scsi/sg.c 1.90 vs edited =====
--- 1.90/drivers/scsi/sg.c	Sat May 29 10:57:23 2004
+++ edited/drivers/scsi/sg.c	Mon Jun 14 22:36:55 2004
@@ -480,6 +480,61 @@
 	return (0 == err) ? count : err;
 }
 
+
+static int
+sg_direction(char *cmnd)
+{
+	switch (cmnd[0]) {
+	/*  _DATA_OUT commands	*/
+	case WRITE_6:		case WRITE_10:		case WRITE_12:
+	case WRITE_16:
+	case WRITE_LONG:	case WRITE_SAME:	case WRITE_BUFFER:
+	case WRITE_VERIFY:	case WRITE_VERIFY_12:
+	case COMPARE:		case COPY:		case COPY_VERIFY:
+	case SEARCH_EQUAL:	case SEARCH_HIGH:	case SEARCH_LOW:
+	case SEARCH_EQUAL_12:	case SEARCH_HIGH_12:	case SEARCH_LOW_12:
+	case MODE_SELECT:	case MODE_SELECT_10:	case LOG_SELECT:
+	case SEND_DIAGNOSTIC:	case CHANGE_DEFINITION: case UPDATE_BLOCK:
+	case SET_WINDOW:	case MEDIUM_SCAN:	case SEND_VOLUME_TAG:
+	case REASSIGN_BLOCKS:
+	case PERSISTENT_RESERVE_OUT:
+	case 0xea:
+	case 0xa3:
+		return SG_DXFER_TO_DEV;
+
+	/*  No data transfer commands  */
+	case SEEK_6:		case SEEK_10:
+	case RESERVE:		case RELEASE:
+	case TEST_UNIT_READY:
+	case START_STOP:
+	case ALLOW_MEDIUM_REMOVAL:
+		return SG_DXFER_NONE;
+
+	/*  Conditional data transfer commands	*/
+	case FORMAT_UNIT:
+		if (cmnd[1] & 0x10)	/* FmtData (data out phase)? */
+			return SG_DXFER_TO_DEV;
+		else
+			return SG_DXFER_NONE;
+
+	case VERIFY:
+		if (cmnd[1] & 0x02)	/* VERIFY:BYTCHK (data out phase)? */
+			return SG_DXFER_TO_DEV;
+		else
+			return SG_DXFER_NONE;
+
+	case RESERVE_10:
+		if (cmnd[1] & 0x03)  /* RESERVE:{LongID|Extent} (data out phase)? */
+			return SG_DXFER_TO_DEV;
+		else
+			return SG_DXFER_NONE;
+
+	/*  Must be data _IN!  */
+	default:
+		return SG_DXFER_FROM_DEV;
+	}
+}
+
 static ssize_t
 sg_write(struct file *filp, const char __user *buf, size_t count, loff_t * ppos)
 {
@@ -552,11 +607,6 @@
 	hp->cmd_len = (unsigned char) cmd_size;
 	hp->iovec_count = 0;
 	hp->mx_sb_len = 0;
-	if (input_size > 0)
-		hp->dxfer_direction = (old_hdr.reply_len > SZ_SG_HEADER) ?
-		    SG_DXFER_TO_FROM_DEV : SG_DXFER_TO_DEV;
-	else
-		hp->dxfer_direction = (mxsize > 0) ? SG_DXFER_FROM_DEV : SG_DXFER_NONE;
 	hp->dxfer_len = mxsize;
 	hp->dxferp = (char __user *)buf + cmd_size;
 	hp->sbp = NULL;
@@ -566,6 +616,18 @@
 	hp->usr_ptr = NULL;
 	if (__copy_from_user(cmnd, buf, cmd_size))
 		return -EFAULT;
+	/*
+	 * If data direction is indeterminate because both input and output size
+	 * are greater than 0, use command bytes to determine direction.
+	 */
+	if (input_size == 0 && mxsize > 0)
+		hp->dxfer_direction = SG_DXFER_FROM_DEV;
+	else if (input_size > 0 && mxsize == 0)
+		hp->dxfer_direction = SG_DXFER_TO_DEV;
+	else if (input_size == 0 && mxsize == 0)
+		hp->dxfer_direction = SG_DXFER_NONE;
+	else
+		hp->dxfer_direction = sg_direction(cmnd);
 	k = sg_common_write(sfp, srp, cmnd, sfp->timeout, blocking);
 	return (k < 0) ? k : count;
 }