[PATCH 18/25] vfs: enable remap callers that can handle short operations

Darrick J. Wong
2018-10-10T00:14:04Z

Plumb in a remap flag that enables the filesystem remap handler to
shorten remapping requests for callers that can handle it. Now
copy_file_range can report partial success (in case we run up against
alignment problems, resource limits, etc.).

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
fs/read_write.c | 3 ++-
include/linux/fs.h | 2 ++
mm/filemap.c | 16 ++++++++++++----
3 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index a628fd9a47cf..8ed0aed81649 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1593,7 +1593,8 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,

cloned = file_in->f_op->remap_file_range(file_in, pos_in,
file_out, pos_out,
- min_t(loff_t, MAX_RW_COUNT, len), 0);
+ min_t(loff_t, MAX_RW_COUNT, len),
+ RFR_CAN_SHORTEN);
if (cloned >= 0) {
ret = cloned;
goto done;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 9f90dcd4df3b..e0494d719ebc 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1726,9 +1726,11 @@ struct block_device_operations;
*
* RFR_IDENTICAL_DATA: only remap if contents identical (i.e. deduplicate)
* RFR_TO_SRC_EOF: remap to the end of the source file
+ * RFR_CAN_SHORTEN: caller can handle a shortened request
*/
#define RFR_IDENTICAL_DATA (1 << 0)
#define RFR_TO_SRC_EOF (1 << 1)
+#define RFR_CAN_SHORTEN (1 << 2)

struct iov_iter;

diff --git a/mm/filemap.c b/mm/filemap.c
index 2522737483de..2179d0204ee6 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3064,8 +3064,12 @@ int generic_remap_checks(struct file *file_in, loff_t pos_in,
if (pos_in + count == size_in) {
bcount = ALIGN(size_in, bs) - pos_in;
} else {
- if (!IS_ALIGNED(count, bs))
- return -EINVAL;
+ if (!IS_ALIGNED(count, bs)) {
+ if (remap_flags & RFR_CAN_SHORTEN)
+ count = ALIGN_DOWN(count, bs);
+ else
+ return -EINVAL;
+ }

bcount = count;
}
@@ -3076,10 +3080,14 @@ int generic_remap_checks(struct file *file_in, loff_t pos_in,
pos_out < pos_in + bcount)
return -EINVAL;

- /* For now we don't support changing the length. */
- if (*req_count != count)
+ /*
+ * We shortened the request but the caller can't deal with that, so
+ * bounce the request back to userspace.
+ */
+ if (*req_count != count && !(remap_flags & RFR_CAN_SHORTEN))
return -EINVAL;

+ *req_count = count;
return 0;
}