[PATCH v10 02/14] fs: export variant of generic_write_checks without iov_iter

[Omar Sandoval <osandov@osandov.com>]

From: Omar Sandoval <osandov@fb.com>

Encoded I/O in Btrfs needs to check a write with a given logical size
without an iov_iter that matches that size (because the iov_iter we have
is for the compressed data). So, factor out the parts of
generic_write_check() that expect an iov_iter into a new
__generic_write_checks() function and export that.

Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 fs/read_write.c    | 40 ++++++++++++++++++++++------------------
 include/linux/fs.h |  1 +
 2 files changed, 23 insertions(+), 18 deletions(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 0029ff2b0ca8..3bddd5ee7f64 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1633,6 +1633,26 @@ int generic_write_check_limits(struct file *file, loff_t pos, loff_t *count)
 	return 0;
 }
 
+/* Like generic_write_checks(), but takes size of write instead of iter. */
+int __generic_write_checks(struct kiocb *iocb, loff_t *count)
+{
+	struct file *file = iocb->ki_filp;
+	struct inode *inode = file->f_mapping->host;
+
+	if (IS_SWAPFILE(inode))
+		return -ETXTBSY;
+
+	/* FIXME: this is for backwards compatibility with 2.4 */
+	if (iocb->ki_flags & IOCB_APPEND)
+		iocb->ki_pos = i_size_read(inode);
+
+	if ((iocb->ki_flags & IOCB_NOWAIT) && !(iocb->ki_flags & IOCB_DIRECT))
+		return -EINVAL;
+
+	return generic_write_check_limits(iocb->ki_filp, iocb->ki_pos, count);
+}
+EXPORT_SYMBOL(__generic_write_checks);
+
 /*
  * Performs necessary checks before doing a write
  *
@@ -1642,26 +1662,10 @@ int generic_write_check_limits(struct file *file, loff_t pos, loff_t *count)
  */
 ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
 {
-	struct file *file = iocb->ki_filp;
-	struct inode *inode = file->f_mapping->host;
-	loff_t count;
+	loff_t count = iov_iter_count(from);
 	int ret;
 
-	if (IS_SWAPFILE(inode))
-		return -ETXTBSY;
-
-	if (!iov_iter_count(from))
-		return 0;
-
-	/* FIXME: this is for backwards compatibility with 2.4 */
-	if (iocb->ki_flags & IOCB_APPEND)
-		iocb->ki_pos = i_size_read(inode);
-
-	if ((iocb->ki_flags & IOCB_NOWAIT) && !(iocb->ki_flags & IOCB_DIRECT))
-		return -EINVAL;
-
-	count = iov_iter_count(from);
-	ret = generic_write_check_limits(file, iocb->ki_pos, &count);
+	ret = __generic_write_checks(iocb, &count);
 	if (ret)
 		return ret;
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 0de4d75339b9..b206814da181 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3227,6 +3227,7 @@ extern int sb_min_blocksize(struct super_block *, int);
 extern int generic_file_mmap(struct file *, struct vm_area_struct *);
 extern int generic_file_readonly_mmap(struct file *, struct vm_area_struct *);
 extern ssize_t generic_write_checks(struct kiocb *, struct iov_iter *);
+extern int __generic_write_checks(struct kiocb *iocb, loff_t *count);
 extern int generic_write_check_limits(struct file *file, loff_t pos,
 		loff_t *count);
 extern int generic_file_rw_checks(struct file *file_in, struct file *file_out);
-- 
2.32.0