Re: regression introduced by "block: Add support for DAX reads/writes to block devices"

Jeff Moyer
2015-08-06T22:25:31Z

"Wilcox, Matthew R" <matthew.r.wilcox@intel.com> writes:

> I think I see the problem. I'm kind of wrapped up in other things
> right now; can you try replacing the line in dax_io():
>
> - bh->b_size = PAGE_ALIGN(end - pos);
> + bh->b_size = ALIGN(end - pos, 1 << blkbits);

This works for me. If it looks okay to others, I'll submit a properly
signed-off patch.

Cheers,
Jeff

diff --git a/fs/dax.c b/fs/dax.c
index a7f77e1..b6c4f93 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -98,6 +98,10 @@ static bool buffer_size_valid(struct buffer_head *bh)
return bh->b_state != 0;
}

+/*
+ * This function assumes file system block size (represented by
+ * inode->i_blkbits) is less than or equal to the system page size.
+ */
static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
loff_t start, loff_t end, get_block_t get_block,
struct buffer_head *bh)
@@ -117,9 +121,15 @@ static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
if (pos == max) {
unsigned blkbits = inode->i_blkbits;
sector_t block = pos >> blkbits;
- unsigned first = pos - (block << blkbits);
+ long page = pos >> PAGE_SHIFT;
+ unsigned first; /* byte offset into block */
long size;

+ /* we can only map entire pages */
+ if (pos & (PAGE_SIZE-1))
+ block = page << (PAGE_SHIFT - blkbits);
+ first = pos - (block << blkbits);
+
if (pos == bh_max) {
bh->b_size = PAGE_ALIGN(end - pos);
bh->b_state = 0;