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iomap: use a srcmap for a read-modify-write I/O

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The srcmap is used to identify where the read is to be performed from.
It is passed to ->iomap_begin, which can fill it in if we need to read
data for partially written blocks from a different location than the
write target.  The srcmap is only supported for buffered writes so far.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
[hch: merged two patches, removed the IOMAP_F_COW flag, use iomap as
      srcmap if not set, adjust length down to srcmap end as well]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Acked-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
This commit is contained in:
Goldwyn Rodrigues
2019-10-18 16:44:10 -07:00
committed by Darrick J. Wong
parent eb81cf9d0e
commit c039b99792
12 changed files with 82 additions and 55 deletions
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13
fs/dax.c
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@@ -1090,7 +1090,7 @@ EXPORT_SYMBOL_GPL(__dax_zero_page_range);
static loff_t
dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
struct iomap *iomap)
struct iomap *iomap, struct iomap *srcmap)
{
struct block_device *bdev = iomap->bdev;
struct dax_device *dax_dev = iomap->dax_dev;
@@ -1247,7 +1247,8 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
struct inode *inode = mapping->host;
unsigned long vaddr = vmf->address;
loff_t pos = (loff_t)vmf->pgoff << PAGE_SHIFT;
struct iomap iomap = { 0 };
struct iomap iomap = { .type = IOMAP_HOLE };
struct iomap srcmap = { .type = IOMAP_HOLE };
unsigned flags = IOMAP_FAULT;
int error, major = 0;
bool write = vmf->flags & FAULT_FLAG_WRITE;
@@ -1292,7 +1293,7 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
* the file system block size to be equal the page size, which means
* that we never have to deal with more than a single extent here.
*/
error = ops->iomap_begin(inode, pos, PAGE_SIZE, flags, &iomap);
error = ops->iomap_begin(inode, pos, PAGE_SIZE, flags, &iomap, &srcmap);
if (iomap_errp)
*iomap_errp = error;
if (error) {
@@ -1471,7 +1472,8 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
unsigned int iomap_flags = (write ? IOMAP_WRITE : 0) | IOMAP_FAULT;
struct inode *inode = mapping->host;
vm_fault_t result = VM_FAULT_FALLBACK;
struct iomap iomap = { 0 };
struct iomap iomap = { .type = IOMAP_HOLE };
struct iomap srcmap = { .type = IOMAP_HOLE };
pgoff_t max_pgoff;
void *entry;
loff_t pos;
@@ -1546,7 +1548,8 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
* to look up our filesystem block.
*/
pos = (loff_t)xas.xa_index << PAGE_SHIFT;
error = ops->iomap_begin(inode, pos, PMD_SIZE, iomap_flags, &iomap);
error = ops->iomap_begin(inode, pos, PMD_SIZE, iomap_flags, &iomap,
&srcmap);
if (error)
goto unlock_entry;