Linux 3.11 compat: fops->iterate()

Commit torvalds/linux@2233f31
replaced ->readdir() with ->iterate() in struct file_operations.
All filesystems must now use the new ->iterate method.

To handle this the code was reworked to use the new ->iterate
interface.  Care was taken to keep the majority of changes
confined to the ZPL layer which is already Linux specific.
However, minor changes were required to the common zfs_readdir()
function.

Compatibility with older kernels was accomplished by adding
versions of the trivial dir_emit* helper functions.  Also the
various *_readdir() functions were reworked in to wrappers
which create a dir_context structure to pass to the new
*_iterate() functions.

Unfortunately, the new dir_emit* functions prevent us from
passing a private pointer to the filldir function.  The xattr
directory code leveraged this ability through zfs_readdir()
to generate the list of xattr names.  Since we can no longer
use zfs_readdir() a simplified zpl_xattr_readdir() function
was added to perform the same task.

Signed-off-by: Richard Yao <ryao@cs.stonybrook.edu>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes openzfs#1653
Issue openzfs#1591

config/kernel-vfs-iterate.m4

@@ -0,0 +1,43 @@
+dnl #
+dnl # 3.11 API change
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_VFS_ITERATE], [
+	AC_MSG_CHECKING([whether fops->iterate() is available])
+	ZFS_LINUX_TRY_COMPILE([
+		#include <linux/fs.h>
+		int iterate(struct file *filp, struct dir_context * context)
+		    { return 0; }
+
+		static const struct file_operations fops
+		    __attribute__ ((unused)) = {
+			.iterate	 = iterate,
+		};
+	],[
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_VFS_ITERATE, 1,
+		          [fops->iterate() is available])
+	],[
+		AC_MSG_RESULT(no)
+
+		AC_MSG_CHECKING([whether fops->readdir() is available])
+		ZFS_LINUX_TRY_COMPILE([
+			#include <linux/fs.h>
+			int readdir(struct file *filp, void *entry, filldir_t func)
+			    { return 0; }
+
+			static const struct file_operations fops
+			    __attribute__ ((unused)) = {
+				.readdir = readdir,
+			};
+		],[
+		],[
+			AC_MSG_RESULT(yes)
+			AC_DEFINE(HAVE_VFS_READDIR, 1,
+				  [fops->readdir() is available])
+		],[
+			AC_MSG_ERROR(no; file a bug report with ZFSOnLinux)
+		])
+
+	])
+])

config/kernel.m4

@@ -81,6 +81,7 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [
 	ZFS_AC_KERNEL_ELEVATOR_CHANGE
 	ZFS_AC_KERNEL_5ARG_SGET
 	ZFS_AC_KERNEL_LSEEK_EXECUTE
+	ZFS_AC_KERNEL_VFS_ITERATE
 
 	AS_IF([test "$LINUX_OBJ" != "$LINUX"], [
 		KERNELMAKE_PARAMS="$KERNELMAKE_PARAMS O=$LINUX_OBJ"

include/sys/zfs_vnops.h

@@ -31,6 +31,7 @@
 #include <sys/cred.h>
 #include <sys/fcntl.h>
 #include <sys/pathname.h>
+#include <sys/zpl.h>
 
 #ifdef	__cplusplus
 extern "C" {
@@ -51,8 +52,7 @@ extern int zfs_mkdir(struct inode *dip, char *dirname, vattr_t *vap,
     struct inode **ipp, cred_t *cr, int flags, vsecattr_t *vsecp);
 extern int zfs_rmdir(struct inode *dip, char *name, struct inode *cwd,
     cred_t *cr, int flags);
-extern int zfs_readdir(struct inode *ip, void *dirent, filldir_t filldir,
-    loff_t *pos, cred_t *cr);
+extern int zfs_readdir(struct inode *ip, struct dir_context *ctx, cred_t *cr);
 extern int zfs_fsync(struct inode *ip, int syncflag, cred_t *cr);
 extern int zfs_getattr(struct inode *ip, vattr_t *vap, int flag, cred_t *cr);
 extern int zfs_getattr_fast(struct inode *ip, struct kstat *sp);

include/sys/zpl.h

@@ -89,4 +89,63 @@ extern const struct inode_operations zpl_ops_snapdirs;
 extern const struct file_operations zpl_fops_shares;
 extern const struct inode_operations zpl_ops_shares;
 
+#ifdef HAVE_VFS_ITERATE
+
+#define DIR_CONTEXT_INIT(_dirent, _actor, _pos) {	\
+	.actor = _actor,				\
+	.pos = _pos,					\
+}
+
+#else
+
+typedef struct dir_context {
+	void *dirent;
+	const filldir_t actor;
+	loff_t pos;
+} dir_context_t;
+
+#define DIR_CONTEXT_INIT(_dirent, _actor, _pos) {	\
+	.dirent = _dirent,				\
+	.actor = _actor,				\
+	.pos = _pos,					\
+}
+
+static inline bool
+dir_emit(struct dir_context *ctx, const char *name, int namelen,
+    uint64_t ino, unsigned type)
+{
+	return ctx->actor(ctx->dirent, name, namelen, ctx->pos, ino, type) == 0;
+}
+
+static inline bool
+dir_emit_dot(struct file *file, struct dir_context *ctx)
+{
+	return ctx->actor(ctx->dirent, ".", 1, ctx->pos,
+	    file->f_path.dentry->d_inode->i_ino, DT_DIR) == 0;
+}
+
+static inline bool
+dir_emit_dotdot(struct file *file, struct dir_context *ctx)
+{
+	return ctx->actor(ctx->dirent, "..", 2, ctx->pos,
+	    parent_ino(file->f_path.dentry), DT_DIR) == 0;
+}
+
+static inline bool
+dir_emit_dots(struct file *file, struct dir_context *ctx)
+{
+	if (ctx->pos == 0) {
+		if (!dir_emit_dot(file, ctx))
+			return false;
+		ctx->pos = 1;
+	}
+	if (ctx->pos == 1) {
+		if (!dir_emit_dotdot(file, ctx))
+			return false;
+		ctx->pos = 2;
+	}
+	return true;
+}
+#endif /* HAVE_VFS_ITERATE */
+
 #endif	/* _SYS_ZPL_H */

module/zfs/zfs_vnops.c

@@ -1997,8 +1997,7 @@ EXPORT_SYMBOL(zfs_rmdir);
  */
 /* ARGSUSED */
 int
-zfs_readdir(struct inode *ip, void *dirent, filldir_t filldir,
-    loff_t *pos, cred_t *cr)
+zfs_readdir(struct inode *ip, struct dir_context *ctx, cred_t *cr)
 {
 	znode_t		*zp = ITOZ(ip);
 	zfs_sb_t	*zsb = ITOZSB(ip);
@@ -2010,6 +2009,7 @@ zfs_readdir(struct inode *ip, void *dirent, filldir_t filldir,
 	uint8_t		prefetch;
 	int		done = 0;
 	uint64_t	parent;
+	loff_t		*pos = &(ctx->pos);
 
 	ZFS_ENTER(zsb);
 	ZFS_VERIFY_ZP(zp);
@@ -2098,11 +2098,11 @@ zfs_readdir(struct inode *ip, void *dirent, filldir_t filldir,
 
 			objnum = ZFS_DIRENT_OBJ(zap.za_first_integer);
 		}
-		done = filldir(dirent, zap.za_name, strlen(zap.za_name),
-			       *pos, objnum, ZFS_DIRENT_TYPE(zap.za_first_integer));
-		if (done) {
+
+		done = !dir_emit(ctx, zap.za_name, strlen(zap.za_name),
+		    objnum, ZFS_DIRENT_TYPE(zap.za_first_integer));
+		if (done)
 			break;
-		}
 
 		/* Prefetch znode */
 		if (prefetch) {