On Fri, Sep 09, 2016 at 06:34:39PM +0200, Christoph Hellwig wrote:
> This is a much simpler implementation of the DAX read/write path that makes
> use of the iomap infrastructure. It does not try to mirror the direct I/O
> calling conventions and thus doesn't have to deal with i_dio_count or the
> end_io handler, but instead leaves locking and filesystem-specific I/O
> completion to the caller.
>
> Signed-off-by: Christoph Hellwig <[email protected]>
> ---
> fs/dax.c | 103
> ++++++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/iomap.h | 2 +
> 2 files changed, 105 insertions(+)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 84343ce..57ad456 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -31,6 +31,8 @@
> #include <linux/vmstat.h>
> #include <linux/pfn_t.h>
> #include <linux/sizes.h>
> +#include <linux/iomap.h>
> +#include "internal.h"
>
> /*
> * We use lowest available bit in exceptional entry for locking, other two
> @@ -1241,3 +1243,104 @@ int dax_truncate_page(struct inode *inode, loff_t
> from, get_block_t get_block)
> return dax_zero_page_range(inode, from, length, get_block);
> }
> EXPORT_SYMBOL_GPL(dax_truncate_page);
> +
> +#ifdef CONFIG_FS_IOMAP
> +static loff_t
> +iomap_dax_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
> + struct iomap *iomap)
> +{
> + struct iov_iter *iter = data;
> + loff_t end = pos + length, done = 0;
> + ssize_t ret = 0;
> +
> + if (iov_iter_rw(iter) == READ) {
> + end = min(end, i_size_read(inode));
> + if (pos >= end)
> + return 0;
> +
> + if (iomap->type == IOMAP_HOLE || iomap->type == IOMAP_UNWRITTEN)
> + return iov_iter_zero(min(length, end - pos), iter);
> + }
> +
> + if (WARN_ON_ONCE(iomap->type != IOMAP_MAPPED))
> + return -EIO;
> +
> + while (pos < end) {
> + unsigned offset = pos & (PAGE_SIZE - 1);
> + struct blk_dax_ctl dax = { 0 };
> + ssize_t map_len;
> +
> + dax.sector = iomap->blkno +
> + (((pos & PAGE_MASK) - iomap->offset) >> 9);
> + dax.size = (length + offset + PAGE_SIZE - 1) & PAGE_MASK;
> + map_len = dax_map_atomic(iomap->bdev, &dax);
> + if (map_len < 0) {
> + ret = map_len;
> + break;
> + }
> +
> + dax.addr += offset;
> + map_len -= offset;
> + if (map_len > end - pos)
> + map_len = end - pos;
> +
> + if (iov_iter_rw(iter) == WRITE)
> + map_len = copy_from_iter_pmem(dax.addr, map_len, iter);
> + else
> + map_len = copy_to_iter(dax.addr, map_len, iter);
> + dax_unmap_atomic(iomap->bdev, &dax);
> + if (map_len <= 0) {
> + ret = map_len ? map_len : -EFAULT;
> + break;
> + }
> +
> + pos += map_len;
> + length -= map_len;
> + done += map_len;
> + }
> +
> + return done ? done : ret;
> +}
> +
> +/**
> + * iomap_dax_rw - Perform I/O to a DAX file
> + * @iocb: The control block for this I/O
> + * @iter: The addresses to do I/O from or to
> + * @ops: iomap ops passed from the file system
> + *
> + * This funtions performs read and write operations to directly mapped
function
> + * persistent memory. The callers needs to take care of read/write exclusion
> + * and evicting any page cache pages in the region under I/O.
> + */
> +ssize_t
> +iomap_dax_rw(struct kiocb *iocb, struct iov_iter *iter,
> + struct iomap_ops *ops)
> +{
> + struct inode *inode = iocb->ki_filp->f_mapping->host;
> + loff_t pos = iocb->ki_pos, ret = 0, done = 0;
Just a note that 'ret' is loff_t about half the time in the iomap code and
ssize_t the other half. I guess it doesn't really matter since they should
both be big unsigned values (64 bits on x96_64), but it's a bit inconsistent.
> + size_t count = iov_iter_count(iter);
> + unsigned flags = 0;
> +
> + if (!count)
> + return 0;
> +
> + if (iov_iter_rw(iter) == WRITE)
> + flags |= IOMAP_WRITE;
> +
> + do {
> + ret = iomap_apply(inode, pos, count, flags, ops, iter,
> + iomap_dax_actor);
> + if (ret <= 0)
> + break;
> + pos += ret;
> + done += ret;
> + } while ((count = iov_iter_count(iter)));
> +
> + if (!done)
> + return ret;
> +
> + iocb->ki_pos += done;
> + return done;
> +}
I think you can remove the special casing around 'done' and 'count' and make
this a bit simpler:
ssize_t
iomap_dax_rw(struct kiocb *iocb, struct iov_iter *iter,
struct iomap_ops *ops)
{
struct inode *inode = iocb->ki_filp->f_mapping->host;
loff_t pos = iocb->ki_pos, ret = 0, done = 0;
unsigned flags = 0;
size_t count;
if (iov_iter_rw(iter) == WRITE)
flags |= IOMAP_WRITE;
while ((count = iov_iter_count(iter))) {
ret = iomap_apply(inode, pos, count, flags, ops, iter,
iomap_dax_actor);
if (ret <= 0)
break;
pos += ret;
done += ret;
}
iocb->ki_pos += done;
return done ? done : ret;
}
This is now very similar to iomap_file_buffered_write().
> +EXPORT_SYMBOL_GPL(iomap_dax_rw);
> +#endif /* CONFIG_FS_IOMAP */
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 14d7067..3d5f785 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -65,6 +65,8 @@ struct iomap_ops {
>
> ssize_t iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *from,
> struct iomap_ops *ops);
> +ssize_t iomap_dax_rw(struct kiocb *iocb, struct iov_iter *iter,
> + struct iomap_ops *ops);
> int iomap_zero_range(struct inode *inode, loff_t pos, loff_t len,
> bool *did_zero, struct iomap_ops *ops);
> int iomap_truncate_page(struct inode *inode, loff_t pos, bool *did_zero,
> --
> 2.1.4
>
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