linux-kernel - [PATCH v2 09/14] s390, dcssblk: Allow a NULL-pfn to ->direct

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Date:   Mon, 16 Jul 2018 10:01:08 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     akpm@...ux-foundation.org
Cc:     Huaisheng Ye <yehs1@...ovo.com>, Jan Kara <jack@...e.cz>,
        vishal.l.verma@...el.com, hch@....de, linux-mm@...ck.org,
        jack@...e.cz, linux-nvdimm@...ts.01.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 09/14] s390,
 dcssblk: Allow a NULL-pfn to ->direct_access()

From: Huaisheng Ye <yehs1@...ovo.com>

dcssblk_direct_access() needs to check the validity of pointer pfn for
NULL assignment. If pfn equals to NULL, it doesn't need to calculate the
value. This is in support of asynchronous memmap init and avoid page
lookups when possible.

Signed-off-by: Huaisheng Ye <yehs1@...ovo.com>
Reviewed-by: Jan Kara <jack@...e.cz>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
 drivers/s390/block/dcssblk.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/block/dcssblk.c b/drivers/s390/block/dcssblk.c
index ed607288e696..a645b2c93c34 100644
--- a/drivers/s390/block/dcssblk.c
+++ b/drivers/s390/block/dcssblk.c
@@ -923,8 +923,9 @@ __dcssblk_direct_access(struct dcssblk_dev_info *dev_info, pgoff_t pgoff,
 
 	dev_sz = dev_info->end - dev_info->start + 1;
 	*kaddr = (void *) dev_info->start + offset;
-	*pfn = __pfn_to_pfn_t(PFN_DOWN(dev_info->start + offset),
-			PFN_DEV|PFN_SPECIAL);
+	if (pfn)
+		*pfn = __pfn_to_pfn_t(PFN_DOWN(dev_info->start + offset),
+				PFN_DEV|PFN_SPECIAL);
 
 	return (dev_sz - offset) / PAGE_SIZE;
 }