[RFC PATCH 1/7] dax: Introduce dax_copy_edges() for COW.

Shiyang Ruan
2019-07-31T11:49:55Z

To copy source data to destance address before write. Change
dax_iomap_pfn() to return the address as well in order to use it for
performing a memcpy in case the type is IOMAP_COW.

dax_copy_edges() is a helper functions performs a copy from one part of
the device to another for data not page aligned.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Signed-off-by: Shiyang Ruan <ruansy.fnst@cn.fujitsu.com>
---
fs/dax.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 52 insertions(+), 4 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 88b93796855e..450baafe2ea4 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -984,7 +984,7 @@ static sector_t dax_iomap_sector(struct iomap *iomap, loff_t pos)
}

static int dax_iomap_pfn(struct iomap *iomap, loff_t pos, size_t size,
- pfn_t *pfnp)
+ pfn_t *pfnp, void **addr)
{
const sector_t sector = dax_iomap_sector(iomap, pos);
pgoff_t pgoff;
@@ -996,11 +996,13 @@ static int dax_iomap_pfn(struct iomap *iomap, loff_t pos, size_t size,
return rc;
id = dax_read_lock();
length = dax_direct_access(iomap->dax_dev, pgoff, PHYS_PFN(size),
- NULL, pfnp);
+ addr, pfnp);
if (length < 0) {
rc = length;
goto out;
}
+ if (!pfnp)
+ goto out_check_addr;
rc = -EINVAL;
if (PFN_PHYS(length) < size)
goto out;
@@ -1010,6 +1012,12 @@ static int dax_iomap_pfn(struct iomap *iomap, loff_t pos, size_t size,
if (length > 1 && !pfn_t_devmap(*pfnp))
goto out;
rc = 0;
+
+out_check_addr:
+ if (!addr)
+ goto out;
+ if (!*addr)
+ rc = -EFAULT;
out:
dax_read_unlock(id);
return rc;
@@ -1084,6 +1092,46 @@ 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 int dax_copy_edges(struct inode *inode, loff_t pos, loff_t length,
+ struct iomap *srcmap, void *daddr)
+{
+ unsigned offset = pos & (PAGE_SIZE - 1);
+ loff_t end = pos + length;
+ loff_t pg_end = round_up(end, PAGE_SIZE);
+ void *saddr = 0;
+ int ret = 0;
+
+ ret = dax_iomap_pfn(srcmap, pos, length, NULL, &saddr);
+ if (ret)
+ return ret;
+ /*
+ * Copy the first part of the page
+ * Note: we pass offset as length
+ */
+ if (offset) {
+ if (saddr)
+ ret = memcpy_mcsafe(daddr, saddr, offset);
+ else
+ memset(daddr, 0, offset);
+ }
+
+ /* Copy the last part of the range */
+ if (end < pg_end) {
+ if (saddr)
+ ret = memcpy_mcsafe(daddr + offset + length,
+ saddr + offset + length, pg_end - end);
+ else
+ memset(daddr + offset + length, 0,
+ pg_end - end);
+ }
+ return ret;
+}
+
static loff_t
dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
struct iomap *iomap, struct iomap *srcmap)
@@ -1338,7 +1386,7 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
count_memcg_event_mm(vma->vm_mm, PGMAJFAULT);
major = VM_FAULT_MAJOR;
}
- error = dax_iomap_pfn(&iomap, pos, PAGE_SIZE, &pfn);
+ error = dax_iomap_pfn(&iomap, pos, PAGE_SIZE, &pfn, NULL);
if (error < 0)
goto error_finish_iomap;

@@ -1555,7 +1603,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,

switch (iomap.type) {
case IOMAP_MAPPED:
- error = dax_iomap_pfn(&iomap, pos, PMD_SIZE, &pfn);
+ error = dax_iomap_pfn(&iomap, pos, PMD_SIZE, &pfn, NULL);
if (error < 0)
goto finish_iomap;

--
2.17.0