So ... what you're doing here is if somebody requests the last 512 bytes,
you're asking for the last page. That's going to work as long as the partition
is a multiple of PAGE_SIZE, but not if the partition happens to be misaligned.
It's an improvement, although I'd be tempted to do this as:
if (pos == max) {
unsigned blkbits = inode->i_blkbits;
- sector_t block = pos >> blkbits;
+ long page = pos >> PAGE_SHIFT;
+ sector_t block = page << (PAGE_SHIFT - blkbits);
unsigned first = pos - (block << blkbits);
long size;
We need to cope with the case where the end of a partition isn't on a page
boundary though.
-----Original Message-----
From: Jeff Moyer [mailto:jmo...@redhat.com]
Sent: Thursday, August 06, 2015 2:31 PM
To: Wilcox, Matthew R
Cc: linda.knipp...@hp.com; linux-kernel@vger.kernel.org;
linux-fsde...@vger.kernel.org
Subject: Re: regression introduced by "block: Add support for DAX reads/writes
to block devices"
"Wilcox, Matthew R" <matthew.r.wil...@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;
--
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