[PATCH] add a file_ra_state init function

Provide a function in core kernel to initialise a file_ra_state structure.

Perviously this was all taken care of by the fact that new struct
file's are all zeroed out.  But now a file_ra_state may be
independently allocated, and we don't want users of it to have to know
how to initialise it.

fs/open.c

@@ -643,7 +643,7 @@ struct file *dentry_open(struct dentry *dentry, struct vfsmount *mnt, int flags)
 			goto cleanup_file;
 	}
 
-	f->f_ra.ra_pages = inode->i_mapping->backing_dev_info->ra_pages;
+	file_ra_state_init(&f->f_ra, inode->i_mapping);
 	f->f_dentry = dentry;
 	f->f_vfsmnt = mnt;
 	f->f_pos = 0;

include/linux/fs.h

@@ -1250,6 +1250,8 @@ ssize_t generic_file_write_nolock(struct file *file, const struct iovec *iov,
 extern ssize_t generic_file_sendfile(struct file *, struct file *, loff_t *, size_t);
 extern void do_generic_mapping_read(struct address_space *, struct file_ra_state *, struct file *,
 				    loff_t *, read_descriptor_t *, read_actor_t);
+extern void
+file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping);
 extern ssize_t generic_file_direct_IO(int rw, struct file *file,
 	const struct iovec *iov, loff_t offset, unsigned long nr_segs);
 extern int generic_direct_IO(int rw, struct inode *inode, struct block_device *bdev,

kernel/ksyms.c

@@ -228,6 +228,7 @@ EXPORT_SYMBOL(generic_block_bmap);
 EXPORT_SYMBOL(generic_file_read);
 EXPORT_SYMBOL(generic_file_sendfile);
 EXPORT_SYMBOL(do_generic_mapping_read);
+EXPORT_SYMBOL(file_ra_state_init);
 EXPORT_SYMBOL(generic_file_write);
 EXPORT_SYMBOL(generic_file_write_nolock);
 EXPORT_SYMBOL(generic_file_mmap);

mm/readahead.c

@@ -19,6 +19,16 @@ struct backing_dev_info default_backing_dev_info = {
 	.state		= 0,
 };
 
+/*
+ * Initialise a struct file's readahead state
+ */
+void
+file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping)
+{
+	memset(ra, 0, sizeof(*ra));
+	ra->ra_pages = mapping->backing_dev_info->ra_pages;
+}
+
 /*
  * Return max readahead size for this inode in number-of-pages.
  */