On Tue, Apr 16, 2019 at 11:41:40AM -0500, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
>
> The IOMAP_DAX_COW is a iomap type which performs copy of
> edges of data while performing a write if start/end are
> not page aligned. The source address is expected in
> iomap->inline_data.
>
> dax_copy_edges() is a helper functions performs a copy from
> one part of the device to another for data not page aligned.
> If iomap->inline_data is NULL, it memset's the area to zero.
>
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
> ---
> fs/dax.c | 41 ++++++++++++++++++++++++++++++++++++++++-
> include/linux/iomap.h | 1 +
> 2 files changed, 41 insertions(+), 1 deletion(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index ca0671d55aa6..4b4ac51fbd16 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -1083,6 +1083,40 @@ int __dax_zero_page_range(struct block_device *bdev,
> }
> EXPORT_SYMBOL_GPL(__dax_zero_page_range);
>
> +/*
> + * dax_copy_edges - Copies the part of the pages not included in
> + * the write, but required for CoW because
> + * offset/offset+length are not page aligned.
> + */
> +static void dax_copy_edges(struct inode *inode, loff_t pos, loff_t length,
> + struct iomap *iomap, void *daddr)
> +{
> + unsigned offset = pos & (PAGE_SIZE - 1);
> + loff_t end = pos + length;
> + loff_t pg_end = round_up(end, PAGE_SIZE);
> + void *saddr = iomap->inline_data;
> + /*
> + * Copy the first part of the page
> + * Note: we pass offset as length
> + */
> + if (offset) {
> + if (saddr)
> + memcpy(daddr, saddr, offset);
I've been wondering, do we need memcpy_mcsafe here?
> + else
> + memset(daddr, 0, offset);
Or here?
(Or any of the other places we call memcpy/memset in this series...)
Because I think we'd prefer to return EIO on bad pmem over a machine
check.
--D
> + }
> +
> + /* Copy the last part of the range */
> + if (end < pg_end) {
> + if (saddr)
> + memcpy(daddr + offset + length,
> + saddr + offset + length, pg_end - end);
> + else
> + memset(daddr + offset + length, 0,
> + pg_end - end);
> + }
> +}
> +
> static loff_t
> dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
> struct iomap *iomap)
> @@ -1104,9 +1138,11 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
> return iov_iter_zero(min(length, end - pos), iter);
> }
>
> - if (WARN_ON_ONCE(iomap->type != IOMAP_MAPPED))
> + if (WARN_ON_ONCE(iomap->type != IOMAP_MAPPED
> + && iomap->type != IOMAP_DAX_COW))
Usually the '&&' goes on the first line, right?
> return -EIO;
>
> +
> /*
> * Write can allocate block for an area which has a hole page mapped
> * into page tables. We have to tear down these mappings so that data
> @@ -1143,6 +1179,9 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
> break;
> }
>
> + if (iomap->type == IOMAP_DAX_COW)
> + dax_copy_edges(inode, pos, length, iomap, kaddr);
No return value? So the pmem copy never fails?
--D
> +
> map_len = PFN_PHYS(map_len);
> kaddr += offset;
> map_len -= offset;
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 0fefb5455bda..6e885c5a38a3 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -25,6 +25,7 @@ struct vm_fault;
> #define IOMAP_MAPPED 0x03 /* blocks allocated at @addr */
> #define IOMAP_UNWRITTEN 0x04 /* blocks allocated at @addr in unwritten state */
> #define IOMAP_INLINE 0x05 /* data inline in the inode */
> +#define IOMAP_DAX_COW 0x06 /* Copy data pointed by inline_data before write*/
>
> /*
> * Flags for all iomap mappings:
> --
> 2.16.4
>
