fs/read_write: Generalize generic_copy_file_checks()

Prepare for adding copy_file_range() support for block devices by making
the following changes:
 - Change file_inode(file) into file->f_mapping->host. Although only one
   inode is associated with regular files, two inodes are associated
   with block devices. file->f_mapping->host is the primary block device
   inode.
 - Change S_ISREG() into S_ISREG() || S_ISBLK().
 - Add an inode->i_mode & S_IFMT check that verifies that source and
   destination have the same type (block device or regular file).

Reviewed-by: Hannes Reinecke <[email protected]>
Signed-off-by: Anuj Gupta <[email protected]>
Signed-off-by: Nitesh Shetty <[email protected]>
[ bvanassche: rewrote patch description ]
Signed-off-by: Bart Van Assche <[email protected]>

Author: Anuj Gupta

fs/read_write.c

@@ -1484,8 +1484,8 @@ static int generic_copy_file_checks(struct file *file_in, loff_t pos_in,
 				    struct file *file_out, loff_t pos_out,
 				    size_t *req_count, unsigned int flags)
 {
-	struct inode *inode_in = file_inode(file_in);
-	struct inode *inode_out = file_inode(file_out);
+	struct inode *inode_in = file_in->f_mapping->host;
+	struct inode *inode_out = file_out->f_mapping->host;
 	uint64_t count = *req_count;
 	loff_t size_in;
 	int ret;
@@ -1791,7 +1791,9 @@ int generic_file_rw_checks(struct file *file_in, struct file *file_out)
 	/* Don't copy dirs, pipes, sockets... */
 	if (S_ISDIR(inode_in->i_mode) || S_ISDIR(inode_out->i_mode))
 		return -EISDIR;
-	if (!S_ISREG(inode_in->i_mode) || !S_ISREG(inode_out->i_mode))
+	if (!S_ISREG(inode_in->i_mode) && !S_ISBLK(inode_in->i_mode))
+		return -EINVAL;
+	if ((inode_in->i_mode & S_IFMT) != (inode_out->i_mode & S_IFMT))
 		return -EINVAL;
 
 	if (!(file_in->f_mode & FMODE_READ) ||