scsi: ppa: use sg helper to iterate over scatterlist

Unlike the legacy I/O path, scsi-mq preallocates a large array to hold
the scatterlist for each request. This static allocation can consume
substantial amounts of memory on modern controllers which support a
large number of concurrently outstanding requests.

To facilitate a switch to a smaller static allocation combined with a
dynamic allocation for requests that need it, we need to make sure all
SCSI drivers handle chained scatterlists correctly.

Convert remaining drivers that directly dereference the scatterlist
array to using the iterator functions.

[mkp: clarified commit message]

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/scsi/ppa.c b/drivers/scsi/ppa.c
index 35213082e933bbeb3510a48efab2da7616185fa7..a406cc825426ca6f5b1de0b48028d5ae2c4ebc00 100644 (file)
--- a/drivers/scsi/ppa.c
+++ b/drivers/scsi/ppa.c
@@ -590,7 +590,7 @@ static int ppa_completion(struct scsi_cmnd *cmd)
                if (cmd->SCp.buffer && !cmd->SCp.this_residual) {
                        /* if scatter/gather, advance to the next segment */
                        if (cmd->SCp.buffers_residual--) {
-                               cmd->SCp.buffer++;
+                               cmd->SCp.buffer = sg_next(cmd->SCp.buffer);
                                cmd->SCp.this_residual =
                                    cmd->SCp.buffer->length;
                                cmd->SCp.ptr = sg_virt(cmd->SCp.buffer);