scsi: imm: 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/imm.c b/drivers/scsi/imm.c
index 64ae418d29f35dfbaa408c4dcdbfae6149c1e0a4..56d29f157749416b10e87754aab77c3e3a52da43 100644 (file)
--- a/drivers/scsi/imm.c
+++ b/drivers/scsi/imm.c
@@ -686,7 +686,7 @@ static int imm_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);