On 5.12.18 г. 14:28 ч., Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgold...@suse.com>
>
> Signed-off-by: Goldwyn Rodrigues <rgold...@suse.com>
> ---
> fs/btrfs/Makefile | 1 +
> fs/btrfs/ctree.h | 5 ++++
> fs/btrfs/dax.c | 68
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> fs/btrfs/file.c | 13 ++++++++++-
> 4 files changed, 86 insertions(+), 1 deletion(-)
> create mode 100644 fs/btrfs/dax.c
>
> diff --git a/fs/btrfs/Makefile b/fs/btrfs/Makefile
> index ca693dd554e9..1fa77b875ae9 100644
> --- a/fs/btrfs/Makefile
> +++ b/fs/btrfs/Makefile
> @@ -12,6 +12,7 @@ btrfs-y += super.o ctree.o extent-tree.o print-tree.o
> root-tree.o dir-item.o \
> reada.o backref.o ulist.o qgroup.o send.o dev-replace.o raid56.o \
> uuid-tree.o props.o free-space-tree.o tree-checker.o
>
> +btrfs-$(CONFIG_FS_DAX) += dax.o
> btrfs-$(CONFIG_BTRFS_FS_POSIX_ACL) += acl.o
> btrfs-$(CONFIG_BTRFS_FS_CHECK_INTEGRITY) += check-integrity.o
> btrfs-$(CONFIG_BTRFS_FS_REF_VERIFY) += ref-verify.o
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 5cc470fa6a40..038d64ecebe5 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -3685,6 +3685,11 @@ int btrfs_reada_wait(void *handle);
> void btrfs_reada_detach(void *handle);
> int btree_readahead_hook(struct extent_buffer *eb, int err);
>
> +#ifdef CONFIG_FS_DAX
> +/* dax.c */
> +ssize_t btrfs_file_dax_read(struct kiocb *iocb, struct iov_iter *to);
> +#endif /* CONFIG_FS_DAX */
> +
> static inline int is_fstree(u64 rootid)
> {
> if (rootid == BTRFS_FS_TREE_OBJECTID ||
> diff --git a/fs/btrfs/dax.c b/fs/btrfs/dax.c
> new file mode 100644
> index 000000000000..d614bf73bf8e
> --- /dev/null
> +++ b/fs/btrfs/dax.c
> @@ -0,0 +1,68 @@
> +#include <linux/dax.h>
> +#include <linux/uio.h>
> +#include "ctree.h"
> +#include "btrfs_inode.h"
> +
> +static ssize_t em_dax_rw(struct inode *inode, struct extent_map *em, u64 pos,
> + u64 len, struct iov_iter *iter)
> +{
> + struct dax_device *dax_dev = fs_dax_get_by_bdev(em->bdev);
> + ssize_t map_len;
> + pgoff_t blk_pg;
> + void *kaddr;
> + sector_t blk_start;
> + unsigned offset = pos & (PAGE_SIZE - 1);
offset = offset_in_page(pos)
> +
> + len = min(len + offset, em->len - (pos - em->start));
> + len = ALIGN(len, PAGE_SIZE);
len = PAGE_ALIGN(len);
> + blk_start = (get_start_sect(em->bdev) << 9) + (em->block_start +
> (pos - em->start));
> + blk_pg = blk_start - offset;
> + map_len = dax_direct_access(dax_dev, PHYS_PFN(blk_pg),
> PHYS_PFN(len), &kaddr, NULL);
> + map_len = PFN_PHYS(map_len)> + kaddr += offset;
> + map_len -= offset;
> + if (map_len > len)
> + map_len = len;
map_len = min(map_len, len);
> + if (iov_iter_rw(iter) == WRITE)
> + return dax_copy_from_iter(dax_dev, blk_pg, kaddr, map_len,
> iter);
> + else
> + return dax_copy_to_iter(dax_dev, blk_pg, kaddr, map_len,
> iter);
Have you looked at the implementation of dax_iomap_actor where they have
pretty similar code. In case of either of those returning 0 they set ret
to EFAULT, should the same be done in btrfs_file_dax_read? IMO it will
be good of you can follow dax_iomap_actor's logic as much as possible
since this code has been used for quite some time and is deemed robust.
> +}
> +
> +ssize_t btrfs_file_dax_read(struct kiocb *iocb, struct iov_iter *to)
> +{
> + size_t ret = 0, done = 0, count = iov_iter_count(to);
> + struct extent_map *em;
> + u64 pos = iocb->ki_pos;
> + u64 end = pos + count;
> + struct inode *inode = file_inode(iocb->ki_filp);
> +
> + if (!count)
> + return 0;
> +
> + end = i_size_read(inode) < end ? i_size_read(inode) : end;
end = min(i_size_read(inode), end)
> +
> + while (pos < end) {
> + u64 len = end - pos;
> +
> + em = btrfs_get_extent(BTRFS_I(inode), NULL, 0, pos, len, 0);
> + if (IS_ERR(em)) {
> + if (!ret)
> + ret = PTR_ERR(em);
> + goto out;
> + }
> +
> + BUG_ON(em->flags & EXTENT_FLAG_FS_MAPPING);
I think this can never trigger, because EXTENT_FLAG_FS_MAPPING is set
for extents that map chunk and those are housed in the chunk tree at
fs_info->mapping_tree. Since the write call back is only ever called for
file inodes I'd say this BUG_ON can be eliminated. Did you manage to
trigger it during development?
> +
> + ret = em_dax_rw(inode, em, pos, len, to);
> + if (ret < 0)
> + goto out;
> + pos += ret;
> + done += ret;
> + }
> +
> +out:
> + iocb->ki_pos += done;
> + return done ? done : ret;
> +}
> +
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index 58e93bce3036..ef6ed93f44d1 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -3308,9 +3308,20 @@ static int btrfs_file_open(struct inode *inode, struct
> file *filp)
> return generic_file_open(inode, filp);
> }
>
> +static ssize_t btrfs_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
> +{
> + struct inode *inode = file_inode(iocb->ki_filp);
> +
> +#ifdef CONFIG_FS_DAX
> + if (IS_DAX(inode))
> + return btrfs_file_dax_read(iocb, to);
> +#endif
> + return generic_file_read_iter(iocb, to);
> +}
> +
> const struct file_operations btrfs_file_operations = {
> .llseek = btrfs_file_llseek,
> - .read_iter = generic_file_read_iter,
> + .read_iter = btrfs_file_read_iter,
> .splice_read = generic_file_splice_read,
> .write_iter = btrfs_file_write_iter,
> .mmap = btrfs_file_mmap,
>
