diff mbox series

[02/10] btrfs: basic dax read

Message ID 20181205122835.19290-3-rgoldwyn@suse.de (mailing list archive)
State New, archived
Headers show
Series btrfs: Support for DAX devices | expand

Commit Message

Goldwyn Rodrigues Dec. 5, 2018, 12:28 p.m. UTC 
From: Goldwyn Rodrigues <rgoldwyn@suse.com>

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@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

Comments

Nikolay Borisov Dec. 5, 2018, 1:11 p.m. UTC | #1 
On 5.12.18 г. 14:28 ч., Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@suse.com>
> 
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@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,
>
Johannes Thumshirn Dec. 5, 2018, 1:22 p.m. UTC | #2 
On 05/12/2018 13:28, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@suse.com>
> 
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Can you explain why we can't use th dax_iomap_rw() interface like XFS or
EXT4?

[...]

> +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);

Nit: unsigned offset = offset_in_page(pos);
diff mbox series

Patch

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);
+
+        len = min(len + offset, em->len - (pos - em->start));
+        len = ALIGN(len, PAGE_SIZE);
+        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;
+        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);
+}
+
+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;
+
+        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);
+
+                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,