scsi: s390: zfcp_fc: use sg helper to iterate over scatterlist [Linux 5.3]

This Linux kernel change "scsi: s390: zfcp_fc: use sg helper to iterate over scatterlist" is included in the Linux 5.3 release. This change is authored by Ming Lei <ming.lei [at] redhat.com> on Tue Jun 18 09:37:51 2019 +0800. The commit for this change in Linux stable tree is 013be03 (patch).

scsi: s390: zfcp_fc: 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]

Cc: Steffen Maier <maier@linux.ibm.com>
Cc: Benjamin Block <bblock@linux.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: linux-s390@vger.kernel.org
Acked-by: Benjamin Block <bblock@linux.ibm.com>
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>

There are 4 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/s390/scsi/zfcp_fc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/scsi/zfcp_fc.c b/drivers/s390/scsi/zfcp_fc.c
index 33eddb0..b018b61 100644
--- a/drivers/s390/scsi/zfcp_fc.c
+++ b/drivers/s390/scsi/zfcp_fc.c
@@ -620,7 +620,7 @@ static void zfcp_fc_sg_free_table(struct scatterlist *sg, int count)
 {
    int i;

-   for (i = 0; i < count; i++, sg++)
+   for (i = 0; i < count; i++, sg = sg_next(sg))
        if (sg)
            free_page((unsigned long) sg_virt(sg));
        else
@@ -641,7 +641,7 @@ static int zfcp_fc_sg_setup_table(struct scatterlist *sg, int count)
    int i;

    sg_init_table(sg, count);
-   for (i = 0; i < count; i++, sg++) {
+   for (i = 0; i < count; i++, sg = sg_next(sg)) {
        addr = (void *) get_zeroed_page(GFP_KERNEL);
        if (!addr) {
            zfcp_fc_sg_free_table(sg, i);

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