scsi: sg: disable SET_FORCE_LOW_DMA

BugLink: http://bugs.launchpad.net/bugs/1754375

commit 745dfa0d upstream.

The ioctl SET_FORCE_LOW_DMA has never worked since the initial git
check-in, and the respective setting is nowadays handled correctly. So
disable it entirely.
Signed-off-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Tested-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/scsi/sg.c

@@ -160,7 +160,6 @@ typedef struct sg_fd {		/* holds the state of a file descriptor */
 	struct list_head rq_list; /* head of request list */
 	struct fasync_struct *async_qp;	/* used by asynchronous notification */
 	Sg_request req_arr[SG_MAX_QUEUE];	/* used as singly-linked list */
-	char low_dma;		/* as in parent but possibly overridden to 1 */
 	char force_packid;	/* 1 -> pack_id input to read(), 0 -> ignored */
 	char cmd_q;		/* 1 -> allow command queuing, 0 -> don't */
 	unsigned char next_cmd_len; /* 0: automatic, >0: use on next write() */
@@ -932,24 +931,14 @@ sg_ioctl(struct file *filp, unsigned int cmd_in, unsigned long arg)
 				/* strange ..., for backward compatibility */
 		return sfp->timeout_user;
 	case SG_SET_FORCE_LOW_DMA:
-		result = get_user(val, ip);
-		if (result)
-			return result;
-		if (val) {
-			sfp->low_dma = 1;
-			if ((0 == sfp->low_dma) && !sfp->res_in_use) {
-				val = (int) sfp->reserve.bufflen;
-				sg_remove_scat(sfp, &sfp->reserve);
-				sg_build_reserve(sfp, val);
-			}
-		} else {
-			if (atomic_read(&sdp->detaching))
-				return -ENODEV;
-			sfp->low_dma = sdp->device->host->unchecked_isa_dma;
-		}
+		/*
+		 * N.B. This ioctl never worked properly, but failed to
+		 * return an error value. So returning '0' to keep compability
+		 * with legacy applications.
+		 */
 		return 0;
 	case SG_GET_LOW_DMA:
-		return put_user((int) sfp->low_dma, ip);
+		return put_user((int) sdp->device->host->unchecked_isa_dma, ip);
 	case SG_GET_SCSI_ID:
 		if (!access_ok(VERIFY_WRITE, p, sizeof (sg_scsi_id_t)))
 			return -EFAULT;
@@ -1870,6 +1859,7 @@ sg_build_indirect(Sg_scatter_hold * schp, Sg_fd * sfp, int buff_size)
 	int sg_tablesize = sfp->parentdp->sg_tablesize;
 	int blk_size = buff_size, order;
 	gfp_t gfp_mask = GFP_ATOMIC | __GFP_COMP | __GFP_NOWARN;
+	struct sg_device *sdp = sfp->parentdp;
 
 	if (blk_size < 0)
 		return -EFAULT;
@@ -1895,7 +1885,7 @@ sg_build_indirect(Sg_scatter_hold * schp, Sg_fd * sfp, int buff_size)
 			scatter_elem_sz_prev = num;
 	}
 
-	if (sfp->low_dma)
+	if (sdp->device->host->unchecked_isa_dma)
 		gfp_mask |= GFP_DMA;
 
 	if (!capable(CAP_SYS_ADMIN) || !capable(CAP_SYS_RAWIO))
@@ -2158,8 +2148,6 @@ sg_add_sfp(Sg_device * sdp)
 	sfp->timeout = SG_DEFAULT_TIMEOUT;
 	sfp->timeout_user = SG_DEFAULT_TIMEOUT_USER;
 	sfp->force_packid = SG_DEF_FORCE_PACK_ID;
-	sfp->low_dma = (SG_DEF_FORCE_LOW_DMA == 0) ?
-	    sdp->device->host->unchecked_isa_dma : 1;
 	sfp->cmd_q = SG_DEF_COMMAND_Q;
 	sfp->keep_orphan = SG_DEF_KEEP_ORPHAN;
 	sfp->parentdp = sdp;
@@ -2618,7 +2606,7 @@ static void sg_proc_debug_helper(struct seq_file *s, Sg_device * sdp)
 			   jiffies_to_msecs(fp->timeout),
 			   fp->reserve.bufflen,
 			   (int) fp->reserve.k_use_sg,
-			   (int) fp->low_dma);
+			   (int) sdp->device->host->unchecked_isa_dma);
 		seq_printf(s, "   cmd_q=%d f_packid=%d k_orphan=%d closed=0\n",
 			   (int) fp->cmd_q, (int) fp->force_packid,
 			   (int) fp->keep_orphan);

include/scsi/sg.h

@@ -197,7 +197,6 @@ typedef struct sg_req_info { /* used by SG_GET_REQUEST_TABLE ioctl() */
 #define SG_DEFAULT_RETRIES 0
 
 /* Defaults, commented if they differ from original sg driver */
-#define SG_DEF_FORCE_LOW_DMA 0  /* was 1 -> memory below 16MB on i386 */
 #define SG_DEF_FORCE_PACK_ID 0
 #define SG_DEF_KEEP_ORPHAN 0
 #define SG_DEF_RESERVED_SIZE SG_SCATTER_SZ /* load time option */