[PATCH 17/25] vfs: enable remap callers that can handle short operations

Darrick J. Wong
2018-10-11T04:14:26Z

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>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
---
fs/read_write.c | 15 +++++++++------
include/linux/fs.h | 7 +++++--
mm/filemap.c | 16 ++++++++++++----
3 files changed, 26 insertions(+), 12 deletions(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 6ec908f9a69b..3713893b7e38 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;
@@ -1804,16 +1805,18 @@ int generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
* If the user is attempting to remap a partial EOF block and
* it's inside the destination EOF then reject it.
*
- * We don't support shortening requests, so we can only reject
- * them.
+ * If possible, shorten the request instead of rejecting it.
*/
if (is_dedupe)
ret = -EBADE;
else if (pos_out + *len < i_size_read(inode_out))
ret = -EINVAL;

- if (ret)
- return ret;
+ if (ret) {
+ if (!(remap_flags & RFR_CAN_SHORTEN))
+ return ret;
+ *len &= ~blkmask;
+ }
}

return 1;
@@ -2112,7 +2115,7 @@ int vfs_dedupe_file_range(struct file *file, struct file_dedupe_range *same)

deduped = vfs_dedupe_file_range_one(file, off, dst_file,
info->dest_offset, len,
- 0);
+ RFR_CAN_SHORTEN);
if (deduped == -EBADE)
info->status = FILE_DEDUPE_RANGE_DIFFERS;
else if (deduped < 0)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b9c314f9d5a4..57cb56bbc30a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1726,14 +1726,17 @@ struct block_device_operations;
*
* RFR_SAME_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_SAME_DATA (1 << 0)
#define RFR_TO_SRC_EOF (1 << 1)
+#define RFR_CAN_SHORTEN (1 << 2)

-#define RFR_VALID_FLAGS (RFR_SAME_DATA | RFR_TO_SRC_EOF)
+#define RFR_VALID_FLAGS (RFR_SAME_DATA | RFR_TO_SRC_EOF | \
+ RFR_CAN_SHORTEN)

/* Implemented by the VFS, so these are advisory. */
-#define RFR_VFS_FLAGS (RFR_TO_SRC_EOF)
+#define RFR_VFS_FLAGS (RFR_TO_SRC_EOF | RFR_CAN_SHORTEN)

/*
* Filesystem remapping implementations should call this helper on their
diff --git a/mm/filemap.c b/mm/filemap.c
index 369cfd164e90..bccbd3621238 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3051,8 +3051,12 @@ 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;
}
@@ -3063,10 +3067,14 @@ 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;
}