[RFC PATCH 2/7] dax: copy data before write.

Shiyang Ruan
2019-07-31T11:52:22Z

Add dax_copy_edges() into each dax actor functions to perform COW in the
case of IOMAP_COW type is set.

Signed-off-by: Shiyang Ruan <ruansy.fnst@cn.fujitsu.com>
---
fs/dax.c | 39 +++++++++++++++++++++++++++++++++------
1 file changed, 33 insertions(+), 6 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 450baafe2ea4..084cc21d47a4 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1098,11 +1098,12 @@ EXPORT_SYMBOL_GPL(__dax_zero_page_range);
* 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)
+ struct iomap *srcmap, void *daddr, bool pmd)
{
- unsigned offset = pos & (PAGE_SIZE - 1);
+ size_t page_size = pmd ? PMD_SIZE : PAGE_SIZE;
+ unsigned offset = pos & (page_size - 1);
loff_t end = pos + length;
- loff_t pg_end = round_up(end, PAGE_SIZE);
+ loff_t pg_end = round_up(end, page_size);
void *saddr = 0;
int ret = 0;

@@ -1153,7 +1154,8 @@ 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_COW))
return -EIO;

/*
@@ -1192,6 +1194,13 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
break;
}

+ if (iomap->type == IOMAP_COW) {
+ ret = dax_copy_edges(inode, pos, length, srcmap, kaddr,
+ false);
+ if (ret)
+ break;
+ }
+
map_len = PFN_PHYS(map_len);
kaddr += offset;
map_len -= offset;
@@ -1300,6 +1309,7 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
vm_fault_t ret = 0;
void *entry;
pfn_t pfn;
+ void *kaddr;

trace_dax_pte_fault(inode, vmf, ret);
/*
@@ -1380,19 +1390,27 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
sync = dax_fault_is_synchronous(flags, vma, &iomap);

switch (iomap.type) {
+ case IOMAP_COW:
case IOMAP_MAPPED:
if (iomap.flags & IOMAP_F_NEW) {
count_vm_event(PGMAJFAULT);
count_memcg_event_mm(vma->vm_mm, PGMAJFAULT);
major = VM_FAULT_MAJOR;
}
- error = dax_iomap_pfn(&iomap, pos, PAGE_SIZE, &pfn, NULL);
+ error = dax_iomap_pfn(&iomap, pos, PAGE_SIZE, &pfn, &kaddr);
if (error < 0)
goto error_finish_iomap;

entry = dax_insert_entry(&xas, mapping, vmf, entry, pfn,
0, write && !sync);

+ if (iomap.type == IOMAP_COW) {
+ error = dax_copy_edges(inode, pos, PAGE_SIZE, &srcmap,
+ kaddr, false);
+ if (error)
+ goto error_finish_iomap;
+ }
+
/*
* If we are doing synchronous page fault and inode needs fsync,
* we can insert PTE into page tables only after that happens.
@@ -1523,6 +1541,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
loff_t pos;
int error;
pfn_t pfn;
+ void *kaddr;

/*
* Check whether offset isn't beyond end of file now. Caller is
@@ -1602,14 +1621,22 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
sync = dax_fault_is_synchronous(iomap_flags, vma, &iomap);

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

entry = dax_insert_entry(&xas, mapping, vmf, entry, pfn,
DAX_PMD, write && !sync);

+ if (iomap.type == IOMAP_COW) {
+ error = dax_copy_edges(inode, pos, PMD_SIZE, &srcmap,
+ kaddr, true);
+ if (error)
+ goto unlock_entry;
+ }
+
/*
* If we are doing synchronous page fault and inode needs fsync,
* we can insert PMD into page tables only after that happens.