sysfs, kernfs: add sysfs_dirent->s_attr.size

sysfs sets the size of regular files unconditionally at PAGE_SIZE and
takes the size of bin files from bin_attribute.  The latter is a
pretty bad interface which forces bin_attribute users to create a
separate copy of bin_attribute for each instance of the file -
e.g. pci resource files.

Add sysfs_dirent->s_attr.size so that the size can be specified
separately.  This unifies inode init paths of ATTR and BIN_ATTR
identical and allows for generic size handling for kernfs.

Unfortunately, this grows the size of sysfs_dirent by sizeof(loff_t).

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/sysfs/file.c

@@ -923,6 +923,7 @@ int sysfs_add_file_mode_ns(struct sysfs_dirent *dir_sd,
 	const struct kernfs_ops *ops;
 	struct sysfs_addrm_cxt acxt;
 	struct sysfs_dirent *sd;
+	loff_t size;
 	int rc;
 
 	if (type == SYSFS_KOBJ_ATTR) {
@@ -943,6 +944,8 @@ int sysfs_add_file_mode_ns(struct sysfs_dirent *dir_sd,
 			ops = &sysfs_file_kfops_wo;
 		else
 			ops = &sysfs_file_kfops_empty;
+
+		size = PAGE_SIZE;
 	} else {
 		struct bin_attribute *battr = (void *)attr;
 
@@ -954,6 +957,8 @@ int sysfs_add_file_mode_ns(struct sysfs_dirent *dir_sd,
 			ops = &sysfs_bin_kfops_wo;
 		else
 			ops = &sysfs_file_kfops_empty;
+
+		size = battr->size;
 	}
 
 	sd = sysfs_new_dirent(attr->name, mode, type);
@@ -961,6 +966,7 @@ int sysfs_add_file_mode_ns(struct sysfs_dirent *dir_sd,
 		return -ENOMEM;
 
 	sd->s_attr.ops = ops;
+	sd->s_attr.size = size;
 	sd->s_ns = ns;
 	sd->priv = (void *)attr;
 	sysfs_dirent_init_lockdep(sd);

fs/sysfs/inode.c

@@ -254,8 +254,6 @@ int sysfs_getattr(struct vfsmount *mnt, struct dentry *dentry,
 
 static void sysfs_init_inode(struct sysfs_dirent *sd, struct inode *inode)
 {
-	struct bin_attribute *bin_attr;
-
 	inode->i_private = sysfs_get(sd);
 	inode->i_mapping->a_ops = &sysfs_aops;
 	inode->i_mapping->backing_dev_info = &sysfs_backing_dev_info;
@@ -271,12 +269,8 @@ static void sysfs_init_inode(struct sysfs_dirent *sd, struct inode *inode)
 		inode->i_fop = &sysfs_dir_operations;
 		break;
 	case SYSFS_KOBJ_ATTR:
-		inode->i_size = PAGE_SIZE;
-		inode->i_fop = &kernfs_file_operations;
-		break;
 	case SYSFS_KOBJ_BIN_ATTR:
-		bin_attr = sd->priv;
-		inode->i_size = bin_attr->size;
+		inode->i_size = sd->s_attr.size;
 		inode->i_fop = &kernfs_file_operations;
 		break;
 	case SYSFS_KOBJ_LINK:

fs/sysfs/sysfs.h

@@ -29,6 +29,7 @@ struct sysfs_elem_symlink {
 struct sysfs_elem_attr {
 	const struct kernfs_ops	*ops;
 	struct sysfs_open_dirent *open;
+	loff_t			size;
 };
 
 struct sysfs_inode_attrs {