linux-kernel - [PATCH v2 7/9] dax: report bytes remaining in dax_iomap

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Message-ID: <152532356340.17218.13406212965402419668.stgit@dwillia2-desk3.amr.corp.intel.com>
Date:   Wed, 02 May 2018 21:59:23 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     linux-nvdimm@...ts.01.org
Cc:     x86@...nel.org, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Tony Luck <tony.luck@...el.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...capital.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>, hch@....de,
        linux-kernel@...r.kernel.org, tony.luck@...el.com,
        linux-fsdevel@...r.kernel.org
Subject: [PATCH v2 7/9] dax: report bytes remaining in dax_iomap_actor()

In preparation for protecting the dax read(2) path from media errors
with copy_to_iter_mcsafe() (via dax_copy_to_iter()), convert the
implementation to report the bytes successfully transferred.

Cc: <x86@...nel.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Tony Luck <tony.luck@...el.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
 fs/dax.c |   20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index a64afdf7ec0d..34a2d435ae4b 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -991,6 +991,7 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 	struct iov_iter *iter = data;
 	loff_t end = pos + length, done = 0;
 	ssize_t ret = 0;
+	size_t xfer;
 	int id;
 
 	if (iov_iter_rw(iter) == READ) {
@@ -1054,19 +1055,20 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 		 * vfs_write(), depending on which operation we are doing.
 		 */
 		if (iov_iter_rw(iter) == WRITE)
-			map_len = dax_copy_from_iter(dax_dev, pgoff, kaddr,
+			xfer = dax_copy_from_iter(dax_dev, pgoff, kaddr,
 					map_len, iter);
 		else
-			map_len = dax_copy_to_iter(dax_dev, pgoff, kaddr,
+			xfer = dax_copy_to_iter(dax_dev, pgoff, kaddr,
 					map_len, iter);
-		if (map_len <= 0) {
-			ret = map_len ? map_len : -EFAULT;
-			break;
-		}
 
-		pos += map_len;
-		length -= map_len;
-		done += map_len;
+		pos += xfer;
+		length -= xfer;
+		done += xfer;
+
+		if (xfer == 0)
+			ret = -EFAULT;
+		if (xfer < map_len)
+			break;
 	}
 	dax_read_unlock(id);