iov_iter: replace iov_iter_copy_from_user_atomic() with iterator-advancing variant

Replacement is called copy_page_from_iter_atomic(); unlike the old primitive the
callers do *not* need to do iov_iter_advance() after it.  In case when they end
up consuming less than they'd been given they need to do iov_iter_revert() on
everything they had not consumed.  That, however, needs to be done only on slow
paths.

All in-tree callers converted.  And that kills the last user of iterate_all_kinds()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

4 files changed, 20 insertions, 24 deletions

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 864c08d08a35..78cb8f9eaa6b 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -398,7 +398,7 @@ static noinline int btrfs_copy_from_user(loff_t pos, size_t write_bytes,
 		/*
 		 * Copy data from userspace to the current page
 		 */
-		copied = iov_iter_copy_from_user_atomic(page, i, offset, count);
+		copied = copy_page_from_iter_atomic(page, offset, count, i);
 
 		/* Flush processor's dcache for this page */
 		flush_dcache_page(page);
@@ -412,20 +412,19 @@ static noinline int btrfs_copy_from_user(loff_t pos, size_t write_bytes,
 		 * The rest of the btrfs_file_write code will fall
 		 * back to page at a time copies after we return 0.
 		 */
-		if (!PageUptodate(page) && copied < count)
-			copied = 0;
+		if (unlikely(copied < count)) {
+			if (!PageUptodate(page)) {
+				iov_iter_revert(i, copied);
+				copied = 0;
+			}
+			if (!copied)
+				break;
+		}
 
-		iov_iter_advance(i, copied);
 		write_bytes -= copied;
 		total_copied += copied;
-
-		/* Return to btrfs_file_write_iter to fault page */
-		if (unlikely(copied == 0))
-			break;
-
-		if (copied < PAGE_SIZE - offset) {
-			offset += copied;
-		} else {
+		offset += copied;
+		if (offset == PAGE_SIZE) {
 			pg++;
 			offset = 0;
 		}
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 44bd301fa4fb..4722fa31a185 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1171,10 +1171,9 @@ static ssize_t fuse_fill_write_pages(struct fuse_io_args *ia,
 		if (mapping_writably_mapped(mapping))
 			flush_dcache_page(page);
 
-		tmp = iov_iter_copy_from_user_atomic(page, ii, offset, bytes);
+		tmp = copy_page_from_iter_atomic(page, offset, bytes, ii);
 		flush_dcache_page(page);
 
-		iov_iter_advance(ii, tmp);
 		if (!tmp) {
 			unlock_page(page);
 			put_page(page);
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 354b41d20e5d..c5ff13e0e7cf 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -785,13 +785,15 @@ again:
 		if (mapping_writably_mapped(inode->i_mapping))
 			flush_dcache_page(page);
 
-		copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
+		copied = copy_page_from_iter_atomic(page, offset, bytes, i);
 
 		status = iomap_write_end(inode, pos, bytes, copied, page, iomap,
 				srcmap);
 
-		cond_resched();
+		if (unlikely(copied != status))
+			iov_iter_revert(i, copied - status);
 
+		cond_resched();
 		if (unlikely(status == 0)) {
 			/*
 			 * A short copy made iomap_write_end() reject the
@@ -803,11 +805,9 @@ again:
 				bytes = copied;
 			goto again;
 		}
-		copied = status;
-		iov_iter_advance(i, copied);
-		pos += copied;
-		written += copied;
-		length -= copied;
+		pos += status;
+		written += status;
+		length -= status;
 
 		balance_dirty_pages_ratelimited(inode->i_mapping);
 	} while (iov_iter_count(i) && length);
diff --git a/fs/ntfs/file.c b/fs/ntfs/file.c
index 0666d4578137..ab4f3362466d 100644
--- a/fs/ntfs/file.c
+++ b/fs/ntfs/file.c
@@ -1690,9 +1690,7 @@ static size_t ntfs_copy_from_user_iter(struct page **pages, unsigned nr_pages,
 		len = PAGE_SIZE - ofs;
 		if (len > bytes)
 			len = bytes;
-		copied = iov_iter_copy_from_user_atomic(*pages, i, ofs,
-				len);
-		iov_iter_advance(i, copied);
+		copied = copy_page_from_iter_atomic(*pages, ofs, len, i);
 		total += copied;
 		bytes -= copied;
 		if (!bytes)