On Tue, Mar 26, 2019 at 02:02:50PM -0500, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
>
> The IOMAP_F_COW is a flag to notify dax that it needs to copy
> the data from iomap->cow_addr to iomap->addr, if the start/end
> of I/O are not page aligned.
>
> This also introduces dax_to_dax_copy() which performs a copy
> from one part of the device to another, to a maximum of one page.
>
> Question: Using iomap.cow_addr == 0 means the CoW is to be copied
> (or memset) from a hole. Would this be better handled through a flag?
>
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
> ---
> fs/dax.c | 36 ++++++++++++++++++++++++++++++++++++
> include/linux/iomap.h | 3 +++
> 2 files changed, 39 insertions(+)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index ca0671d55aa6..e254535dd830 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -1051,6 +1051,28 @@ static bool dax_range_is_aligned(struct block_device *bdev,
> return true;
> }
>
> +static void dax_to_dax_copy(struct iomap *iomap, loff_t pos, void *daddr,
> + size_t len)
> +{
> + loff_t blk_start, blk_pg;
> + void *saddr;
> + ssize_t map_len;
> +
> + /* A zero address is a hole. */
> + if (iomap->cow_addr == 0) {
> + memset(daddr, 0, len);
> + return;
> + }
> +
> + blk_start = iomap->cow_addr + pos - iomap->cow_pos;
> + blk_pg = round_down(blk_start, PAGE_SIZE);
> +
> + map_len = dax_direct_access(iomap->dax_dev, PHYS_PFN(blk_pg), PAGE_SIZE,
> + &saddr, NULL);
> + saddr += blk_start - blk_pg;
> + memcpy(daddr, saddr, len);
> +}
> +
> int __dax_zero_page_range(struct block_device *bdev,
> struct dax_device *dax_dev, sector_t sector,
> unsigned int offset, unsigned int size)
> @@ -1143,6 +1165,20 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
> break;
> }
>
> + if (iomap->flags & IOMAP_F_COW) {
> + loff_t pg_end = round_up(end, PAGE_SIZE);
> + /*
> + * Copy the first part of the page
> + * Note: we pass offset as length
> + */
> + if (offset)
> + dax_to_dax_copy(iomap, pos - offset, kaddr, offset);
> +
> + /* Copy the last part of the range */
> + if (end < pg_end)
> + dax_to_dax_copy(iomap, end, kaddr + offset + length, pg_end - end);
> + }
> +
> 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..391785de1428 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
Probably a good idea to cc the iomap maintainers on this (entire
patchset)... <cough>
--D
> @@ -35,6 +35,7 @@ struct vm_fault;
> #define IOMAP_F_NEW 0x01 /* blocks have been newly allocated */
> #define IOMAP_F_DIRTY 0x02 /* uncommitted metadata */
> #define IOMAP_F_BUFFER_HEAD 0x04 /* file system requires buffer heads */
> +#define IOMAP_F_COW 0x08 /* cow before write */
>
> /*
> * Flags that only need to be reported for IOMAP_REPORT requests:
> @@ -59,6 +60,8 @@ struct iomap {
> u64 length; /* length of mapping, bytes */
> u16 type; /* type of mapping */
> u16 flags; /* flags for mapping */
> + u64 cow_addr; /* read address to perform CoW */
> + loff_t cow_pos; /* file offset of cow_addr */
> struct block_device *bdev; /* block device for I/O */
> struct dax_device *dax_dev; /* dax_dev for dax operations */
> void *inline_data;
> --
> 2.16.4
>
