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Subject[PATCH v3 7/9] dax: report bytes remaining in dax_iomap_actor()
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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@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.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);

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