[readdir] introduce ->iterate(), ctx->pos, dir_emit()

New method - ->iterate(file, ctx).  That's the replacement for ->readdir();
it takes callback from ctx->actor, uses ctx->pos instead of file->f_pos and
calls dir_emit(ctx, ...) instead of filldir(data, ...).  It does *not*
update file->f_pos (or look at it, for that matter); iterate_dir() does the
update.

Note that dir_emit() takes the offset from ctx->pos (and eventually
filldir_t will lose that argument).
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/parisc/hpux/fs.c

@@ -129,7 +129,7 @@ int hpux_getdents(unsigned int fd, struct hpux_dirent __user *dirent, unsigned i
 		error = buf.error;
 	lastdirent = buf.previous;
 	if (lastdirent) {
-		if (put_user(arg.file->f_pos, &lastdirent->d_off))
+		if (put_user(buf.ctx.pos, &lastdirent->d_off))
 			error = -EFAULT;
 		else
 			error = count - buf.count;

fs/coda/dir.c

@@ -391,8 +391,7 @@ static int coda_readdir(struct file *coda_file, void *buf, filldir_t filldir)
 	if (!host_file->f_op)
 		return -ENOTDIR;
 
-	if (host_file->f_op->readdir)
-	{
+	if (host_file->f_op->readdir) {
 		/* potemkin case: we were handed a directory inode.
 		 * We can't use vfs_readdir because we have to keep the file
 		 * position in sync between the coda_file and the host_file.
@@ -410,8 +409,20 @@ static int coda_readdir(struct file *coda_file, void *buf, filldir_t filldir)
 
 		coda_file->f_pos = host_file->f_pos;
 		mutex_unlock(&host_inode->i_mutex);
-	}
-	else /* Venus: we must read Venus dirents from a file */
+	} else if (host_file->f_op->iterate) {
+		struct inode *host_inode = file_inode(host_file);
+		struct dir_context *ctx = buf;
+
+		mutex_lock(&host_inode->i_mutex);
+		ret = -ENOENT;
+		if (!IS_DEADDIR(host_inode)) {
+			ret = host_file->f_op->iterate(host_file, ctx);
+			file_accessed(host_file);
+		}
+		mutex_unlock(&host_inode->i_mutex);
+
+		coda_file->f_pos = ctx->pos;
+	} else /* Venus: we must read Venus dirents from a file */
 		ret = coda_venus_readdir(coda_file, buf, filldir);
 
 	return ret;

fs/compat.c

@@ -975,7 +975,7 @@ asmlinkage long compat_sys_getdents(unsigned int fd,
 		error = buf.error;
 	lastdirent = buf.previous;
 	if (lastdirent) {
-		if (put_user(f.file->f_pos, &lastdirent->d_off))
+		if (put_user(buf.ctx.pos, &lastdirent->d_off))
 			error = -EFAULT;
 		else
 			error = count - buf.count;
@@ -1062,7 +1062,7 @@ asmlinkage long compat_sys_getdents64(unsigned int fd,
 		error = buf.error;
 	lastdirent = buf.previous;
 	if (lastdirent) {
-		typeof(lastdirent->d_off) d_off = f.file->f_pos;
+		typeof(lastdirent->d_off) d_off = buf.ctx.pos;
 		if (__put_user_unaligned(d_off, &lastdirent->d_off))
 			error = -EFAULT;
 		else

fs/exportfs/expfs.c

@@ -272,7 +272,7 @@ static int get_name(const struct path *path, char *name, struct dentry *child)
 		goto out;
 
 	error = -EINVAL;
-	if (!file->f_op->readdir)
+	if (!file->f_op->readdir && !file->f_op->iterate)
 		goto out_close;
 
 	buffer.name = name;

fs/nfsd/nfs4recover.c

@@ -240,11 +240,16 @@ struct name_list {
 	struct list_head list;
 };
 
+struct nfs4_dir_ctx {
+	struct dir_context ctx;
+	struct list_head names;
+};
+
 static int
 nfsd4_build_namelist(void *arg, const char *name, int namlen,
 		loff_t offset, u64 ino, unsigned int d_type)
 {
-	struct list_head *names = arg;
+	struct nfs4_dir_ctx *ctx = arg;
 	struct name_list *entry;
 
 	if (namlen != HEXDIR_LEN - 1)
@@ -254,7 +259,7 @@ nfsd4_build_namelist(void *arg, const char *name, int namlen,
 		return -ENOMEM;
 	memcpy(entry->name, name, HEXDIR_LEN - 1);
 	entry->name[HEXDIR_LEN - 1] = '\0';
-	list_add(&entry->list, names);
+	list_add(&entry->list, &ctx->names);
 	return 0;
 }
 
@@ -263,10 +268,7 @@ nfsd4_list_rec_dir(recdir_func *f, struct nfsd_net *nn)
 {
 	const struct cred *original_cred;
 	struct dentry *dir = nn->rec_file->f_path.dentry;
-	struct {
-		struct dir_context ctx;
-		struct list_head names;
-	} ctx;
+	struct nfs4_dir_ctx ctx;
 	int status;
 
 	status = nfs4_save_creds(&original_cred);

fs/readdir.c

@@ -24,7 +24,7 @@ int iterate_dir(struct file *file, struct dir_context *ctx)
 {
 	struct inode *inode = file_inode(file);
 	int res = -ENOTDIR;
-	if (!file->f_op || !file->f_op->readdir)
+	if (!file->f_op || (!file->f_op->readdir && !file->f_op->iterate))
 		goto out;
 
 	res = security_file_permission(file, MAY_READ);
@@ -37,7 +37,14 @@ int iterate_dir(struct file *file, struct dir_context *ctx)
 
 	res = -ENOENT;
 	if (!IS_DEADDIR(inode)) {
-		res = file->f_op->readdir(file, ctx, ctx->actor);
+		if (file->f_op->iterate) {
+			ctx->pos = file->f_pos;
+			res = file->f_op->iterate(file, ctx);
+			file->f_pos = ctx->pos;
+		} else {
+			res = file->f_op->readdir(file, ctx, ctx->actor);
+			ctx->pos = file->f_pos;
+		}
 		file_accessed(file);
 	}
 	mutex_unlock(&inode->i_mutex);
@@ -214,7 +221,7 @@ SYSCALL_DEFINE3(getdents, unsigned int, fd,
 		error = buf.error;
 	lastdirent = buf.previous;
 	if (lastdirent) {
-		if (put_user(f.file->f_pos, &lastdirent->d_off))
+		if (put_user(buf.ctx.pos, &lastdirent->d_off))
 			error = -EFAULT;
 		else
 			error = count - buf.count;
@@ -296,7 +303,7 @@ SYSCALL_DEFINE3(getdents64, unsigned int, fd,
 		error = buf.error;
 	lastdirent = buf.previous;
 	if (lastdirent) {
-		typeof(lastdirent->d_off) d_off = f.file->f_pos;
+		typeof(lastdirent->d_off) d_off = buf.ctx.pos;
 		if (__put_user(d_off, &lastdirent->d_off))
 			error = -EFAULT;
 		else

include/linux/fs.h

@@ -1508,7 +1508,15 @@ int fiemap_check_flags(struct fiemap_extent_info *fieinfo, u32 fs_flags);
 typedef int (*filldir_t)(void *, const char *, int, loff_t, u64, unsigned);
 struct dir_context {
 	filldir_t actor;
+	loff_t pos;
 };
+
+static inline bool dir_emit(struct dir_context *ctx,
+			    const char *name, int namelen,
+			    u64 ino, unsigned type)
+{
+	return ctx->actor(ctx, name, namelen, ctx->pos, ino, type) == 0;
+}
 struct block_device_operations;
 
 /* These macros are for out of kernel modules to test that
@@ -1525,6 +1533,7 @@ struct file_operations {
 	ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
 	ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
 	int (*readdir) (struct file *, void *, filldir_t);
+	int (*iterate) (struct file *, struct dir_context *);
 	unsigned int (*poll) (struct file *, struct poll_table_struct *);
 	long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
 	long (*compat_ioctl) (struct file *, unsigned int, unsigned long);