scoutfs: support newer ->iterate readdir

The modern upstream kernel has a ->iterate() readdir file_operattions
method which takes a context and calls dir_emit().   We add some
kernelcompat helpers to juggle the various function definitions, types,
and arguments to support both the old ->readdir(filldir) and the new
->iterate(ctx) interfaces.

Signed-off-by: Zach Brown <zab@versity.com>

kmod/src/Makefile.kernelcompat

@@ -5,3 +5,32 @@
 #
 
 ccflags-y += -include $(src)/kernelcompat.h
+
+#
+# v3.10-rc6-21-gbb6f619b3a49
+#
+# _readdir changes from fop->readdir() to fop->iterate() and from
+# filldir(dirent) to dir_emit(ctx).
+#
+ifneq (,$(shell grep 'iterate.*dir_context' include/linux/fs.h))
+ccflags-y += -DKC_ITERATE_DIR_CONTEXT
+endif
+
+#
+# v3.10-rc6-23-g5f99f4e79abc
+#
+# Helpers including dir_emit_dots() are added in the process of
+# switching dcache_readdir() from fop->readdir() to fop->iterate()
+#
+ifneq (,$(shell grep 'dir_emit_dots' include/linux/fs.h))
+ccflags-y += -DKC_DIR_EMIT_DOTS
+endif
+
+#
+# RHEL extended the fop struct so to use it we have to set
+# a flag to indicate that the struct is large enough and
+# contains the pointer.
+#
+ifneq (,$(shell grep 'FMODE_KABI_ITERATE' include/linux/fs.h))
+ccflags-y += -DKC_FMODE_KABI_ITERATE
+endif

kmod/src/dir.c

@@ -436,28 +436,6 @@ out:
 	return d_splice_alias(inode, dentry);
 }
 
-/* this exists upstream so we can just delete it in a forward port */
-static int dir_emit_dots(struct file *file, void *dirent, filldir_t filldir)
-{
-	struct dentry *dentry = file->f_path.dentry;
-	struct inode *inode = dentry->d_inode;
-	struct inode *parent = dentry->d_parent->d_inode;
-
-	if (file->f_pos == 0) {
-		if (filldir(dirent, ".", 1, 1, scoutfs_ino(inode), DT_DIR))
-			return 0;
-		file->f_pos = 1;
-	}
-
-	if (file->f_pos == 1) {
-		if (filldir(dirent, "..", 2, 1, scoutfs_ino(parent), DT_DIR))
-			return 0;
-		file->f_pos = 2;
-	}
-
-	return 1;
-}
-
 /*
  * readdir simply iterates over the dirent items for the dir inode and
  * uses their offset as the readdir position.
@@ -465,7 +443,8 @@ static int dir_emit_dots(struct file *file, void *dirent, filldir_t filldir)
  * It will need to be careful not to read past the region of the dirent
  * hash offset keys that it has access to.
  */
-static int scoutfs_readdir(struct file *file, void *dirent, filldir_t filldir)
+static int KC_DECLARE_READDIR(scoutfs_readdir, struct file *file,
+			      void *dirent, kc_readdir_ctx_t ctx)
 {
 	struct inode *inode = file_inode(file);
 	struct super_block *sb = inode->i_sb;
@@ -478,7 +457,7 @@ static int scoutfs_readdir(struct file *file, void *dirent, filldir_t filldir)
 	u64 pos;
 	int ret;
 
-	if (!dir_emit_dots(file, dirent, filldir))
+	if (!kc_dir_emit_dots(file, dirent, ctx))
 		return 0;
 
 	dent = alloc_dirent(SCOUTFS_NAME_LEN);
@@ -497,7 +476,7 @@ static int scoutfs_readdir(struct file *file, void *dirent, filldir_t filldir)
 
 	for (;;) {
 		init_dirent_key(&key, SCOUTFS_READDIR_TYPE, scoutfs_ino(inode),
-				file->f_pos, 0);
+				kc_readdir_pos(file, ctx), 0);
 
 		ret = scoutfs_item_next(sb, &key, &last_key, &val, dir_lock);
 		if (ret < 0) {
@@ -511,21 +490,24 @@ static int scoutfs_readdir(struct file *file, void *dirent, filldir_t filldir)
 			scoutfs_corruption(sb, SC_DIRENT_READDIR_NAME_LEN,
 					   corrupt_dirent_readdir_name_len,
 					   "dir_ino %llu pos %llu key "SK_FMT" len %d",
-					   scoutfs_ino(inode), file->f_pos,
+					   scoutfs_ino(inode),
+					   kc_readdir_pos(file, ctx),
 					   SK_ARG(&key), name_len);
 			ret = -EIO;
 			goto out;
 		}
 
 		pos = le64_to_cpu(key.skd_major);
+		kc_readdir_pos(file, ctx) = pos;
 
-		if (filldir(dirent, dent->name, name_len, pos,
+		if (!kc_dir_emit(ctx, dent, dent->name, name_len, pos,
-			    le64_to_cpu(dent->ino), dentry_type(dent->type))) {
+				le64_to_cpu(dent->ino),
+				dentry_type(dent->type))) {
 			ret = 0;
 			break;
 		}
 
-		file->f_pos = pos + 1;
+		kc_readdir_pos(file, ctx) = pos + 1;
 	}
 
 out:
@@ -1737,8 +1719,20 @@ out_unlock:
 	return ret;
 }
 
+#ifdef KC_FMODE_KABI_ITERATE
+/* we only need this to set the iterate flag for kabi :/ */
+static int scoutfs_dir_open(struct inode *inode, struct file *file)
+{
+        file->f_mode |= FMODE_KABI_ITERATE;
+        return 0;
+}
+#endif
+
 const struct file_operations scoutfs_dir_fops = {
-	.readdir	= scoutfs_readdir,
+	.KC_FOP_READDIR	= scoutfs_readdir,
+#ifdef KC_FMODE_KABI_ITERATE
+	.open		= scoutfs_dir_open,
+#endif
 	.unlocked_ioctl	= scoutfs_ioctl,
 	.fsync		= scoutfs_file_fsync,
 	.llseek		= generic_file_llseek,

kmod/src/kernelcompat.h

@@ -1,4 +1,49 @@
 #ifndef _SCOUTFS_KERNELCOMPAT_H_
 #define _SCOUTFS_KERNELCOMPAT_H_
 
+#ifndef KC_ITERATE_DIR_CONTEXT
+#include <linux/fs.h>
+typedef filldir_t kc_readdir_ctx_t;
+#define KC_DECLARE_READDIR(name, file, dirent, ctx) name(file, dirent, ctx)
+#define KC_FOP_READDIR readdir
+#define kc_readdir_pos(filp, ctx) (filp)->f_pos
+#define kc_dir_emit_dots(file, dirent, ctx) dir_emit_dots(file, dirent, ctx)
+#define kc_dir_emit(ctx, dentry, name, name_len, pos, ino, dt) \
+	(ctx(dentry, name, name_len, pos, ino, dt) == 0)
+#else
+typedef struct dir_context * kc_readdir_ctx_t;
+#define KC_DECLARE_READDIR(name, file, dirent, ctx) name(file, ctx)
+#define KC_FOP_READDIR iterate
+#define kc_readdir_pos(filp, ctx) (ctx)->pos
+#define kc_dir_emit_dots(file, dirent, ctx) dir_emit_dots(file, ctx)
+#define kc_dir_emit(ctx, dentry, name, name_len, pos, ino, dt) \
+	dir_emit(ctx, name, name_len, ino, dt)
+#endif
+
+#ifndef KC_DIR_EMIT_DOTS
+/*
+ * Kernels before ->iterate and don't have dir_emit_dots so we give them
+ * one that works with the ->readdir() filldir() method.
+ */
+static inline int dir_emit_dots(struct file *file, void *dirent,
+				filldir_t filldir)
+{
+	if (file->f_pos == 0) {
+		if (filldir(dirent, ".", 1, 1,
+			    file->f_path.dentry->d_inode->i_ino, DT_DIR))
+			return 0;
+		file->f_pos = 1;
+	}
+
+	if (file->f_pos == 1) {
+		if (filldir(dirent, "..", 2, 1,
+			    parent_ino(file->f_path.dentry), DT_DIR))
+			return 0;
+		file->f_pos = 2;
+	}
+
+	return 1;
+}
+#endif
+
 #endif