[SCSI] sg: cap reserved_size values at max_sectors

This patch (as857) modifies the SG_GET_RESERVED_SIZE and
SG_SET_RESERVED_SIZE ioctls in the sg driver, capping the values at
the device's request_queue's max_sectors value.  This will permit
cdrecord to obtain a legal value for the maximum transfer length,
fixing Bugzilla #7026.

The patch also caps the initial reserved_size value.  There's no
reason to have a reserved buffer larger than max_sectors, since it
would be impossible to use the extra space.

The corresponding ioctls in the block layer are modified similarly,
and the initial value for the reserved_size is set as large as
possible.  This will effectively make it default to max_sectors.
Note that the actual value is meaningless anyway, since block devices
don't have a reserved buffer.

Finally, the BLKSECTGET ioctl is added to sg, so that there will be a
uniform way for users to determine the actual max_sectors value for
any raw SCSI transport.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Jens Axboe <jens.axboe@oracle.com>
Acked-by: Douglas Gilbert <dougg@torque.net>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

3 files changed, 16 insertions, 3 deletions

diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index 38c293b987b7..cf8752abd61a 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -1925,6 +1925,8 @@ blk_init_queue_node(request_fn_proc *rfn, spinlock_t *lock, int node_id)
         blk_queue_max_hw_segments(q, MAX_HW_SEGMENTS);
         blk_queue_max_phys_segments(q, MAX_PHYS_SEGMENTS);
 
+        q->sg_reserved_size = INT_MAX;
+
         /*
          * all done
          */
diff --git a/block/scsi_ioctl.c b/block/scsi_ioctl.c
index 65c6a3cba6d6..e83f1dbf7c29 100644
--- a/block/scsi_ioctl.c
+++ b/block/scsi_ioctl.c
@@ -78,7 +78,9 @@ static int sg_set_timeout(request_queue_t *q, int __user *p)
 
 static int sg_get_reserved_size(request_queue_t *q, int __user *p)
 {
-        return put_user(q->sg_reserved_size, p);
+        unsigned val = min(q->sg_reserved_size, q->max_sectors << 9);
+
+        return put_user(val, p);
 }
 
 static int sg_set_reserved_size(request_queue_t *q, int __user *p)
diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 81e3bc7b02a1..570977cf9efb 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -917,6 +917,8 @@ sg_ioctl(struct inode *inode, struct file *filp,
                         return result;
                 if (val < 0)
                         return -EINVAL;
+                val = min_t(int, val,
+                                sdp->device->request_queue->max_sectors * 512);
                 if (val != sfp->reserve.bufflen) {
                         if (sg_res_in_use(sfp) || sfp->mmap_called)
                                 return -EBUSY;
@@ -925,7 +927,8 @@ sg_ioctl(struct inode *inode, struct file *filp,
                 }
                 return 0;
         case SG_GET_RESERVED_SIZE:
-                val = (int) sfp->reserve.bufflen;
+                val = min_t(int, sfp->reserve.bufflen,
+                                sdp->device->request_queue->max_sectors * 512);
                 return put_user(val, ip);
         case SG_SET_COMMAND_Q:
                 result = get_user(val, ip);
@@ -1061,6 +1064,9 @@ sg_ioctl(struct inode *inode, struct file *filp,
                 if (sdp->detached)
                         return -ENODEV;
                 return scsi_ioctl(sdp->device, cmd_in, p);
+        case BLKSECTGET:
+                return put_user(sdp->device->request_queue->max_sectors * 512,
+                                ip);
         default:
                 if (read_only)
                         return -EPERM;  /* don't know so take safe approach */
@@ -2339,6 +2345,7 @@ sg_add_sfp(Sg_device * sdp, int dev)
 {
         Sg_fd *sfp;
         unsigned long iflags;
+        int bufflen;
 
         sfp = kzalloc(sizeof(*sfp), GFP_ATOMIC | __GFP_NOWARN);
         if (!sfp)
@@ -2369,7 +2376,9 @@ sg_add_sfp(Sg_device * sdp, int dev)
         if (unlikely(sg_big_buff != def_reserved_size))
                 sg_big_buff = def_reserved_size;
 
-        sg_build_reserve(sfp, sg_big_buff);
+        bufflen = min_t(int, sg_big_buff,
+                        sdp->device->request_queue->max_sectors * 512);
+        sg_build_reserve(sfp, bufflen);
         SCSI_LOG_TIMEOUT(3, printk("sg_add_sfp:   bufflen=%d, k_use_sg=%d\n",
                            sfp->reserve.bufflen, sfp->reserve.k_use_sg));
         return sfp;