um: hostfs: Reduce number of syscalls in readdir

Currently hostfs issues every time a seekdir(), in fact
it has to do this only upon the first call.
Also telldir() can be omitted as we can obtain the directory
offset from readdir().
Signed-off-by: NRichard Weinberger <richard@nod.at>

fs/hostfs/hostfs.h

@@ -66,7 +66,8 @@ extern int stat_file(const char *path, struct hostfs_stat *p, int fd);
 extern int access_file(char *path, int r, int w, int x);
 extern int open_file(char *path, int r, int w, int append);
 extern void *open_dir(char *path, int *err_out);
-extern char *read_dir(void *stream, unsigned long long *pos,
+extern void seek_dir(void *stream, unsigned long long pos);
+extern char *read_dir(void *stream, unsigned long long *pos_out,
 		      unsigned long long *ino_out, int *len_out,
 		      unsigned int *type_out);
 extern void close_file(void *stream);

fs/hostfs/hostfs_kern.c

@@ -292,6 +292,7 @@ static int hostfs_readdir(struct file *file, struct dir_context *ctx)
 	if (dir == NULL)
 		return -error;
 	next = ctx->pos;
+	seek_dir(dir, next);
 	while ((name = read_dir(dir, &next, &ino, &len, &type)) != NULL) {
 		if (!dir_emit(ctx, name, len, ino, type))
 			break;

fs/hostfs/hostfs_user.c

@@ -97,21 +97,27 @@ void *open_dir(char *path, int *err_out)
 	return dir;
 }
 
-char *read_dir(void *stream, unsigned long long *pos,
+void seek_dir(void *stream, unsigned long long pos)
+{
+	DIR *dir = stream;
+
+	seekdir(dir, pos);
+}
+
+char *read_dir(void *stream, unsigned long long *pos_out,
 	       unsigned long long *ino_out, int *len_out,
 	       unsigned int *type_out)
 {
 	DIR *dir = stream;
 	struct dirent *ent;
 
-	seekdir(dir, *pos);
 	ent = readdir(dir);
 	if (ent == NULL)
 		return NULL;
 	*len_out = strlen(ent->d_name);
 	*ino_out = ent->d_ino;
 	*type_out = ent->d_type;
-	*pos = telldir(dir);
+	*pos_out = ent->d_off;
 	return ent->d_name;
 }