[PATCH] Fix filesystems that cannot do mmap writeback

The writepage-removal patch broke filesystems which do not want to
support writeable mappings.

Fix that up by making those filesystems point their mmap vector at the
new generic_file_readonly_mmap().

fs/afs/file.c

@@ -37,7 +37,7 @@ struct inode_operations afs_file_inode_operations = {
 struct file_operations afs_file_file_operations = {
 	.read		= generic_file_read,
 	.write		= afs_file_write,
-	.mmap		= generic_file_mmap,
+	.mmap		= generic_file_readonly_mmap,
 #if 0
 	.open		= afs_file_open,
 	.release	= afs_file_release,

fs/befs/linuxvfs.c

@@ -74,7 +74,7 @@ struct inode_operations befs_dir_inode_operations = {
 struct file_operations befs_file_operations = {
 	.llseek		= default_llseek,
 	.read		= generic_file_read,
-	.mmap		= generic_file_mmap,
+	.mmap		= generic_file_readonly_mmap,
 };
 
 struct address_space_operations befs_aops = {

fs/jffs/inode-v23.c

@@ -1641,7 +1641,7 @@ static struct file_operations jffs_file_operations =
 	.read		= generic_file_read,
 	.write		= generic_file_write,
 	.ioctl		= jffs_ioctl,
-	.mmap		= generic_file_mmap,
+	.mmap		= generic_file_readonly_mmap,
 	.fsync		= jffs_fsync,
 	.sendfile	= generic_file_sendfile,
 };

fs/jffs2/file.c

@@ -58,7 +58,7 @@ struct file_operations jffs2_file_operations =
 	.read =		generic_file_read,
 	.write =	generic_file_write,
 	.ioctl =	jffs2_ioctl,
-	.mmap =		generic_file_mmap,
+	.mmap =		generic_file_readonly_mmap,
 	.fsync =	jffs2_fsync,
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(2,5,29)
 	.sendfile =	generic_file_sendfile

fs/read_write.c

@@ -19,7 +19,7 @@
 struct file_operations generic_ro_fops = {
 	.llseek		= generic_file_llseek,
 	.read		= generic_file_read,
-	.mmap		= generic_file_mmap,
+	.mmap		= generic_file_readonly_mmap,
 	.sendfile	= generic_file_sendfile,
 };
 

include/linux/fs.h

@@ -1233,6 +1233,7 @@ extern int sb_set_blocksize(struct super_block *, int);
 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 int file_read_actor(read_descriptor_t * desc, struct page *page, unsigned long offset, unsigned long size);
 extern int file_send_actor(read_descriptor_t * desc, struct page *page, unsigned long offset, unsigned long size);
 extern ssize_t generic_file_read(struct file *, char *, size_t, loff_t *);

kernel/ksyms.c

@@ -228,6 +228,7 @@ EXPORT_SYMBOL(file_ra_state_init);
 EXPORT_SYMBOL(generic_file_write);
 EXPORT_SYMBOL(generic_file_write_nolock);
 EXPORT_SYMBOL(generic_file_mmap);
+EXPORT_SYMBOL(generic_file_readonly_mmap);
 EXPORT_SYMBOL(generic_ro_fops);
 EXPORT_SYMBOL(file_lock_list);
 EXPORT_SYMBOL(locks_init_lock);

mm/filemap.c

@@ -1293,6 +1293,14 @@ int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
 	vma->vm_ops = &generic_file_vm_ops;
 	return 0;
 }
+
+int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE))
+		return -EINVAL;
+	vma->vm_flags &= ~VM_MAYWRITE;
+	return generic_file_mmap(file, vma);
+}
 #else
 int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
 {