[PATCH RFC 10/11] fs: move generic_file_read_iter() to fs/read_write.c

[Tal Zussman]

generic_file_read_iter() and its kiocb_write_and_wait() helper are
VFS-level read functions: Their callers are filesystems, and their job
is to glue direct I/O or the page cache (filemap_read) to a struct kiocb
and iov_iter caller.

Move both to fs/read_write.c, alongside vfs_iter_read. Drop the extern
from generic_file_read_iter()'s declaration and reflow the
generic_file_read_iter() definition to fit on one line too.

Signed-off-by: Tal Zussman <tz2294@xxxxxxxxxxxx>
---
 fs/read_write.c         | 82 +++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/fs.h      |  3 +-
 include/linux/pagemap.h |  1 -
 mm/filemap.c            | 82 -------------------------------------------------
 4 files changed, 84 insertions(+), 84 deletions(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 50bff7edc91f..59ceea85c163 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -989,6 +989,88 @@ ssize_t vfs_iter_write(struct file *file, struct iov_iter *iter, loff_t *ppos,
 }
 EXPORT_SYMBOL(vfs_iter_write);
 
+int kiocb_write_and_wait(struct kiocb *iocb, size_t count)
+{
+	struct address_space *mapping = iocb->ki_filp->f_mapping;
+	loff_t pos = iocb->ki_pos;
+	loff_t end = pos + count - 1;
+
+	if (iocb->ki_flags & IOCB_NOWAIT) {
+		if (filemap_range_needs_writeback(mapping, pos, end))
+			return -EAGAIN;
+		return 0;
+	}
+
+	return filemap_write_and_wait_range(mapping, pos, end);
+}
+EXPORT_SYMBOL_GPL(kiocb_write_and_wait);
+
+/**
+ * generic_file_read_iter - generic filesystem read routine
+ * @iocb:	kernel I/O control block
+ * @iter:	destination for the data read
+ *
+ * This is the "read_iter()" routine for all filesystems
+ * that can use the page cache directly.
+ *
+ * The IOCB_NOWAIT flag in iocb->ki_flags indicates that -EAGAIN shall
+ * be returned when no data can be read without waiting for I/O requests
+ * to complete; it doesn't prevent readahead.
+ *
+ * The IOCB_NOIO flag in iocb->ki_flags indicates that no new I/O
+ * requests shall be made for the read or for readahead.  When no data
+ * can be read, -EAGAIN shall be returned.  When readahead would be
+ * triggered, a partial, possibly empty read shall be returned.
+ *
+ * Return:
+ * * number of bytes copied, even for partial reads
+ * * negative error code (or 0 if IOCB_NOIO) if nothing was read
+ */
+ssize_t generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
+{
+	size_t count = iov_iter_count(iter);
+	ssize_t retval = 0;
+
+	if (!count)
+		return 0; /* skip atime */
+
+	if (iocb->ki_flags & IOCB_DIRECT) {
+		struct file *file = iocb->ki_filp;
+		struct address_space *mapping = file->f_mapping;
+		struct inode *inode = mapping->host;
+
+		retval = kiocb_write_and_wait(iocb, count);
+		if (retval < 0)
+			return retval;
+		file_accessed(file);
+
+		retval = mapping->a_ops->direct_IO(iocb, iter);
+		if (retval >= 0) {
+			iocb->ki_pos += retval;
+			count -= retval;
+		}
+		if (retval != -EIOCBQUEUED)
+			iov_iter_revert(iter, count - iov_iter_count(iter));
+
+		/*
+		 * Btrfs can have a short DIO read if we encounter
+		 * compressed extents, so if there was an error, or if
+		 * we've already read everything we wanted to, or if
+		 * there was a short read because we hit EOF, go ahead
+		 * and return.  Otherwise fallthrough to buffered io for
+		 * the rest of the read.  Buffered reads will not work for
+		 * DAX files, so don't bother trying.
+		 */
+		if (retval < 0 || !count || IS_DAX(inode))
+			return retval;
+		if (iocb->ki_pos >= i_size_read(inode))
+			return retval;
+	}
+
+	return filemap_read(iocb, iter, retval);
+}
+EXPORT_SYMBOL(generic_file_read_iter);
+
 static ssize_t vfs_readv(struct file *file, const struct iovec __user *vec,
 			 unsigned long vlen, loff_t *pos, rwf_t flags)
 {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 776cc82932a7..c0151ced8e7a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3055,7 +3055,8 @@ extern int generic_write_check_limits(struct file *file, loff_t pos,
 extern int generic_file_rw_checks(struct file *file_in, struct file *file_out);
 ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *to,
 		ssize_t already_read);
-extern ssize_t generic_file_read_iter(struct kiocb *, struct iov_iter *);
+ssize_t generic_file_read_iter(struct kiocb *, struct iov_iter *);
+int kiocb_write_and_wait(struct kiocb *iocb, size_t count);
 extern ssize_t __generic_file_write_iter(struct kiocb *, struct iov_iter *);
 extern ssize_t generic_file_write_iter(struct kiocb *, struct iov_iter *);
 extern ssize_t generic_file_direct_write(struct kiocb *, struct iov_iter *);
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index f86a550ad516..46cefd552a51 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -59,7 +59,6 @@ int filemap_fdatawrite_range(struct address_space *mapping,
 		loff_t start, loff_t end);
 int filemap_check_errors(struct address_space *mapping);
 void __filemap_set_wb_err(struct address_space *mapping, int err);
-int kiocb_write_and_wait(struct kiocb *iocb, size_t count);
 
 static inline int filemap_write_and_wait(struct address_space *mapping)
 {
diff --git a/mm/filemap.c b/mm/filemap.c
index 079f9c3ac8a2..db7c53cd681b 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2251,22 +2251,6 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter,
 }
 EXPORT_SYMBOL_GPL(filemap_read);
 
-int kiocb_write_and_wait(struct kiocb *iocb, size_t count)
-{
-	struct address_space *mapping = iocb->ki_filp->f_mapping;
-	loff_t pos = iocb->ki_pos;
-	loff_t end = pos + count - 1;
-
-	if (iocb->ki_flags & IOCB_NOWAIT) {
-		if (filemap_range_needs_writeback(mapping, pos, end))
-			return -EAGAIN;
-		return 0;
-	}
-
-	return filemap_write_and_wait_range(mapping, pos, end);
-}
-EXPORT_SYMBOL_GPL(kiocb_write_and_wait);
-
 int filemap_invalidate_pages(struct address_space *mapping,
 			     loff_t pos, loff_t end, bool nowait)
 {
@@ -2302,72 +2286,6 @@ int kiocb_invalidate_pages(struct kiocb *iocb, size_t count)
 }
 EXPORT_SYMBOL_GPL(kiocb_invalidate_pages);
 
-/**
- * generic_file_read_iter - generic filesystem read routine
- * @iocb:	kernel I/O control block
- * @iter:	destination for the data read
- *
- * This is the "read_iter()" routine for all filesystems
- * that can use the page cache directly.
- *
- * The IOCB_NOWAIT flag in iocb->ki_flags indicates that -EAGAIN shall
- * be returned when no data can be read without waiting for I/O requests
- * to complete; it doesn't prevent readahead.
- *
- * The IOCB_NOIO flag in iocb->ki_flags indicates that no new I/O
- * requests shall be made for the read or for readahead.  When no data
- * can be read, -EAGAIN shall be returned.  When readahead would be
- * triggered, a partial, possibly empty read shall be returned.
- *
- * Return:
- * * number of bytes copied, even for partial reads
- * * negative error code (or 0 if IOCB_NOIO) if nothing was read
- */
-ssize_t
-generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
-{
-	size_t count = iov_iter_count(iter);
-	ssize_t retval = 0;
-
-	if (!count)
-		return 0; /* skip atime */
-
-	if (iocb->ki_flags & IOCB_DIRECT) {
-		struct file *file = iocb->ki_filp;
-		struct address_space *mapping = file->f_mapping;
-		struct inode *inode = mapping->host;
-
-		retval = kiocb_write_and_wait(iocb, count);
-		if (retval < 0)
-			return retval;
-		file_accessed(file);
-
-		retval = mapping->a_ops->direct_IO(iocb, iter);
-		if (retval >= 0) {
-			iocb->ki_pos += retval;
-			count -= retval;
-		}
-		if (retval != -EIOCBQUEUED)
-			iov_iter_revert(iter, count - iov_iter_count(iter));
-
-		/*
-		 * Btrfs can have a short DIO read if we encounter
-		 * compressed extents, so if there was an error, or if
-		 * we've already read everything we wanted to, or if
-		 * there was a short read because we hit EOF, go ahead
-		 * and return.  Otherwise fallthrough to buffered io for
-		 * the rest of the read.  Buffered reads will not work for
-		 * DAX files, so don't bother trying.
-		 */
-		if (retval < 0 || !count || IS_DAX(inode))
-			return retval;
-		if (iocb->ki_pos >= i_size_read(inode))
-			return retval;
-	}
-
-	return filemap_read(iocb, iter, retval);
-}
-EXPORT_SYMBOL(generic_file_read_iter);
 
 /*
  * Splice subpages from a folio into a pipe.

-- 
2.39.5